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Experimenting With Trap Dipoles- Part Numero Uno

The Project and Situation: After quite a bit of trying over the past 15 years to find the best way to pull dipoles up into the closely packed trees in the yard it is clear the options are limited. Having the dipoles favor the NE/SW directions are the goal, but the arrangement of the best supports make this difficult. To beat this problem a combination of single band and multi band fan dipoles were used. [No, the “chainsaw solution” is not an option – yet.]

The primary supports are now occupied with supporting a 160m inverted L and another with a vee dipole for 80m. These are not high enough for direction to make much difference, but are in convenient locations. So everything else needs to fit around those two primary constraints.

The current problem is that there is really only one support that easily allows stretching out the legs of a 40m dipole in the desired directions while also achieving a good height for 40m(almost 50′). The other high supports will only allow the antenna to be deployed favoring a N/S direction(i.e., legs are stretched out E/W).

Using fan dipoles has come with its own practical problems. The dense tree branch coverage tends to tangle in the multiple wires of the legs. Then the fan legs have become entangled in heavy winds. So it is both a problem deploying the antennas, but also the SWR issues when legs are entangled after bad WX. An ongoing maintenance issue.

Alternate solution: trap dipoles. With dual band trap dipoles, it seems like it may be easier to arrange the antennas in favorable directions AND at good heights. The traps are relatively small compared to the mess of multiple wires on a fan, so also maybe it will be a bit easier to navigate dense branch cover of the biological deciduous antenna support structures. The downside is in the extra effort required in constructing the traps, tuning them to desired frequencies, and tuning the antenna legs for each desired band.

What’s the frequency, Kenneth?!? Using EzNEC 6 I ran models with trap data. Based on those results I initially decided to use traps tuned for just above the top frequencies of any given band(e.g., on 20m tuned for 14.400). I’m willing to live with the trap losses for the advantage of maintenance simplicity. Models showed tuning traps for the top end resulted in wire lengths that are the same as a single band dipole, or slightly longer. I then chose to build antennas with traps above the high end of the band based on the following.

  1. A trap resonant frequency above the band results in the dipole wires being the same length or slightly longer than the single band dipole at the trap frequency
  2. A trap resonant frequency below the band requires the dipole wires to be shorter than a dipole for that band. This might be worth pursuing if trying to reduce the antenna length.
  3. there were already a few spare dipoles laying about, and if the traps project flopped they would still be usable mostly intact if traps designed above band,
  4. I’ll probably be mostly using them on CW so maybe a tad less loss with trap rez at opposite end
  5. the gut feeling that a 20m trap resonated at 13.900 would maybe have more loss than the trap at 14.4 when used at 14.025.
  6. NOTE: SEE Part 2 for notes on how these initial assumptions changed!

Research: The traps will inevitably add unwanted weight to the antennas, and I wished to keep them as lightweight as possible. The reasoning for light weight was to extend the project to portable dipoles deployable on telescoping fiberglass masts. So I ruled out using one of the many coaxial trap designs simply to save weight where possible. For coil forms I chose to use small pieces of 1.5″ plumbing waste pipe cut from small sections of what is sold in the US as a “drain tail piece”. This is thin wall pipe, and much lighter than ordinary schedule 40 PVC. The second form material tried AND ABANDONED is 3.4 inch PVC sched 40.

Excluding the coax trap articles, there are relatively few trap dipole projects written up or documented in places accessible via internet searches. The best[most relevant] source is an ARRL antenna book article on a 2 band trap dipole. W8JI also has some interesting trap info published. Although it does not cover the specifics on the options I chose, it led me to the final result. My choices were made based on materials already on hand(wire, capacitors, and coil form material). Engineer the possible.

Initial Trap Construction: The available values of capacitors also drove the selection of trap resonant frequencies. On this point I made an effort to follow W8JI’s information and make the traps resonant off of the desired operating frequencies to minimize trap losses. Beyond this guideline I could locate nowhere any info to indicate if certain values of inductance vs capacitance were better or worse. A larger inductor will allow the antenna to be shorter overall, but the length of the dipole legs was not a restricting parameter for my project. This was merely about having the dipole resonant on 2 bands. Also, the capacitors are 2KV and 3KV 5% tolerance ceramics from Panasonic that I have used previously in band pass filter projects with great success. (NOTE: MORE ON THIS LATER!!!)

Coil Guidelines????: Guidelines for winding the coils are also a bit of guesswork, beyond W8JI’s testing results that show the highest losses occur on the resonant frequency of the trap. I simply started with the inductors, targeting a value of 6uh, initial turns counts generated by a random calculator found via internet search. Then trial and error on actual coil winding. Calculated inductances are based on trap resonant frequency measurements recorded and on the assumption the 5% caps were the most accurate component. Inductances are then calculated from cap face values and resonant frequency.

Test coils for the traps were close wound with #14 THHN stranded housing wire. They were close wound by hand as tightly as possible onto the forms. Coil Q is probably lower than it could be, but the close winding was a compromise accepted for ease of construction and ease of replication. Four inch lengths of 1.5″ waste pipe and three inch lengths of 3/4 inch PVC were tried. The latter were discarded as unsuitable.

Experimenting With the Coils and Caps: The 5% Panasonic caps on hand typically measure very close to the marked nominal values, much better than any 5% or 10% silver mica caps I have used in similar projects. I found that coils wound with similar technique and the same number of turns would reliably resonate within a range of +/-100 to 200hz. Generally the accuracy and reproducibility is better at 7 and 14 Mhz than at 28Mhz. The coils at the higher frequencies have fewer turns, and smaller differences in inductance and capacitance have a larger effect on resonance.

A group of several capacitor values were used along with an MFJ-259C as a grid dip meter to find the resonant frequencies. Pickup coupling coil was a coax jumper terminated on the business end with gator clips and a short length of #14 wire formed into an adjustable sized loop.

Some initial experimenting with the number of turns on the inductors was based on these available values of fixed capacitors. The first inductor was 12 turns on the 1.5″ forms, then resonance was tested with the values of capacitance that were on hand, or able to be easily derived using series and parallel pairs. It was then relatively simple to find the number of turns needed to be able to produce a trap resonant at a given frequency. I also wound coils on the same form material using 7 and 9 turns, and measured resonance for these.

Experimenting With Trap Dipoles- Part 2

 

Telescoping Fiberglass Mast – Variations On A Theme

I have been using a telescoping fiberglass mast of one sort or another since 2005 or so. Most folks seem to be using these masts mostly as designed, i.e. relying on the friction fit, or using tape or hose clamps to keep the mast extended under load. None of those seemed ideal for my plans to use them with dipoles(inverted V config).

The first pole I obtained was from Henry, K4TMC (tmastco.com).(FWIW, I am acquainted with Henry via our membership in PVRC. Henry also sold me a very nice Elecraft K2 when he upgraded to the K3, and other assorted sections of surplus mast.)

This is the 32 foot pole, which results in about 29-30 foot of usable length once extended. Relying on friction fit, I ran into a couple of problems I think common to ALL of these similar type masts. The first problem is the amount of friction required to keep the poles from collapsing was also enough to make them difficult to collapse in very hot or very cold weather.(38C/98F or 0C/32F) Tape and hose clamps are usually enough to resolve that, but bring their own issues.

Tape tends to leave a lot of residue at the joint at 38C(i.e., ‘sticky mess’), which is a problem on sandy beaches. Sand does not enhance the experience of using one of these masts when it sticks to the joints. I also did not like the amount of pressure hose clamps required, nor the amount of time needed to install them in correct order(at 98F oceanside), or to fasten them without crushing the fiberglass accidentally. Because of “spontaneous collapsing” under certain types of pressure, the friction fit is not ideal for use with dipoles, my preferred antenna for portable ops.

The solution I chose was to drill the mast and use 1/8 or 3/32 cotter pins at the bottom of sections just above where they rest when extended. The pin rests on top of the next lower section, so no problems trying to align holes through two sections. Saving another 1000 words……

A section of mast extended showing position of pin, which goes through only the base of the single section.

Over the past 10 years or so I have acquired a few additional masts. Primarily to have the ability to deploy more than a single antenna, but also as redundant or spare masts. [Two is one, one is none.] These additional masts include the 12m Spiderbeam pole, both a 28 and 32 foot mast from Jackite, a 22 foot mast that was marketed as a flagpole, and several Shakespeare 20 foot Wonderpoles. The Wonderpoles are used mostly to elevate the ends of the dipole legs when it seems appropriate(mostly constricted spaces).

The mast from K4TMC has seen the most use over the last decade. It has a good combination of stiffness and flexibility for its length. I had my doubts about drilling holes for the cotter pins, but the mast has been deployed for extended periods with little signs of anything more than minor cosmetic damage. The Spiderbeam mast seems to be much more flexible, which tends to negate is useful length as a center support for dipoles. Both Jackite masts seem to be the most rigid of the group, but I have used these less than any of the others – they are relatively new buys.

The disappointment of the group for me is the Spiderbeam mast. Its flexibility requires guying to keep it from noodling with the weight of a very light weight 40m dipole made of 18ga wire. Best practice seems to be best to attach the feedline to the mast for any of these type masts, but absolutely essential with the Spiderbeam. My Spiderbeam pole also becomes difficult to extend to its full length the more it bends, although that does help keep it from spontaneous collapse. Also more difficult to deploy in heavy wind at the beach due to flexibility, common to all but more pronounced on the Spiderbeam. The other masts are more self supporting when used with the auger bases. This may indeed have more to do with their overall shorter length, and the spiderbeam masts are indeed intended to be guyed by the manufacturer. I would prefer not to use guys to save time, but in several excursions I was unable to use the full length of the Spiderbeam mast sans guy lines. Even with guys the Spiderbeam pole had excessive droop in high winds oceanside, so the additional time required did not seem worth the effort. Taken all together the Spiderbeam mast was not taking my dipole significantly higher than shorter masts.

Auger Bases? Why didn’t I think of that? : The other divergence from the norm is my use of these auger bases. These auger bases are items I have scrounged from different sources. The first pair of them I obtained from Harbor Freight in the early 2000’s, where they were being marketed as beach umbrella stands. That source disappeared soon after my purchase. A second group of smaller augers[NOT pictured below] are marketed as “Aussie Augers”, but needed modification to use with the fiberglass masts(unless you don’t mind removing the end caps from the bottom).

These augers pictured below were available via Amazon in the US in 2019. They work extremely well in sand. They are heavier gauge material than the Harbor Freight versions. The larger tapered base is my first choice for sand and seems to be the strongest. It would also work anywhere with a deep layer of loam or sandy topsoil. The base with the narrow welded on auger is more useful where the soil is less friendly, with stone or tree roots. I use the narrow base in my home yard, which is chock full of quartz stones and tree roots. It sometimes requires multiple placement attempts, but seldom takes more than a few minutes to install. For areas with no topsoil, shallow stone, or mountains, this solution might be less than ideal. The other caveat is leaving a hole in the deployment area.

Both bases are about 60cm in length(22 inches) and have a 60-61mm throat width(approx 2-3/8 inches). This is just barely wide enough for the Spiderbeam mast to fit without removing the base cap. All of the other masts are a bit smaller at the base and fit in easily. The large base has a depth about 178mm(7 inches) and the larger a depth of 127mm(5 inches). FWIW, with the smaller diameter masts I often insert a section of 2″ PVC into the base as a bushing sleeve, and the mast into the PVC bushing section.
Large tapered base at Amazon [American Ground Screw Model 2]
Narrow welded base at Amazon [American Ground Screw Model 1 with Cap ]

I don’t expect I have been the first to go down this less traveled path but have not seen it documented elsewhere. So some photos above for reference. I drilled 9/64 holes in the bottom of each nested section, just ABOVE the joints, and use 1/8 cotter pins.

My 10+ year old mast from K4TMC has been deployed numerous times. There is still only minor wear to the drilled holes, and zero cracking or vertical splits. YMMV. Caveat Emptor. An additional tip would be to have spare pins, and pins in at least two lengths. The bits of wire are used to keep the pins from vibrating loose in the ocean breeze. The also are used with coax to keep the feedline close to the mast. Generally I tape the feedline when using twinlead.

The choice of feedline is made on deployment depending on the distance from the antenna to the operating position. I use LMR240/RFC240 for the feedline drops when the operating position is close to the antenna, and 300 ohm ladderline from DX engineering for long runs.

FD 2018 with masts deployed

FD 2018 photos

2018 IOTA using single K4TMC mast

2018 IOTA K4Z photos

2018 IOTA K4Z time lapse mast deployment video

Mast Hoisting and IOTA Pages

2015 IOTA W4O at Okracoke with N4YDU

??more??

Red Pitaya SDR as Core of CW Skimmer – Part 2, Notes and Updates

Additional Red Pitaya CW skimmer notes, last update 2018-08-22
for original detailed post see:  Red Pitaya SDR as Core of CW Skimmer – Part 1
Notes and Updates
2019-02-01

Note 4, RX Antenna:  The skimmer system is now using the 3.8 wave inverted L as its RX antenna full time.  The only anticipated interruptions will be occasional 160m contests.

2018-08-22:

Note 1:  Skimmer station outage in mid July 2018, cause appears to be rx antenna related.

Note 2, Transformer:  N6TV identified a mini circuits 14:1 transformer that is suitable for use with the Red Pitaya on RX.  Expect the transformer to be available from Red Pitaya, or occasionally N6TV.  Available from mini-circuits vendors, but may be expensive in quantity 1.

Note 3, RX antenna:  Some what by accident I discovered that the 160m L I use for transmit seems to make a fine all-band rx antenna for the Red Pitaya skimmer set up.  FWIW, the antenna is about 140 feet of wire.  About 60-70 feet vertical, with the remainder making a dog-leg turn from top of vertical section.  From there it runs horizontally  NW to second support about 40 feet away, and a second sharper turn to the east, horizontally and slightly downward for the remainder which runs west to east.  The radial system is the K2AV type folded counterpoise system described in more detail at link.

Field Day 2018 – 1B NC de W4KAZ

The normal group of Field Day scalawags were in the wind for 2018.  N4GU was uncertain if the QTH from 2016 and 2017 would be available.  N4YDU took up N9NB’s offer for FD at Ted’s QTH in VA foothills.  I was also kindly invited, but decided that I didn’t want to drive quite that far, despite the nearly ideal location.  I do love me some VA mountains.

Photos from FD2018: http://w4kaz.com/images/fd2018/

For 2018 I took exit ramp #3, and went with the backup backup plan.  Operated 1B at a campground near Wilmington NC.  A nice easy drive, with a couple of easy on/off stops along the way to stretch out the body parts complaining loudest.  That made the drive tolerable.   Also made it into a mini-escape, leaving home QTH on Thursday with a return on Monday morning.

Weather conditions[i.e., heat] soon had me thinking I’d have been better off in the VA mountains, but after acclimatizing to “swamp butt” conditions, it was fine.  When I sweat enough to remind me of living on the South coast – its pretty darn sticky.  Usually not quite so bad in NC, but it happens enough to know to be prepared.  Lots of water and gatorade.  Thursday afternoon was the worst of it though.

Friday morning was spent doing a bit of unrelated recon.  Friday afternoon I laid out the antennas and supports, and some more unrelated area wide explorations.  WX on Saturday dryed out some, and there was a nice breeze that picked up from the start of operations though early evening.  Never a drop of rain, just temps and humidity in the 90’s.  Just like being back in good ole Bigg Swampy(SE Louisiana).

Antennas:

2018 was a time to test some antenna ideas.  I built a 2 band triangular yagi for 20m/15m, based on article by Herb,N4HA as published in June 2018 QST.  I kept to the published dimensions(mostly) but fashioned the driven element(s) from 300ohm ladder line.  For supports I used a mast from Henry, K4TMC as the support for the drive element/apex.  The tails sloped down to connect to the reflectors, and those ends were supported by 2 masts cobbled together by combining a Shakespeare Wonderpole on top of a section of 4 foot mil surplus mast.   Simple, and easier than I expected.  This antenna was fed with 300 ohm ladder line run to a tuner rather than coax.

40m was a simple inverted Vee supported by a Spiderbeam 12m telescoping mast.  Note: Simple does not mean “easy”.

10m was an afterthought.  After struggling with the 40m dipole-that-wouldn’t, I had a relaxing breakfast and gave some thought to 10m.  Had plenty of time, so may as well.  To get on 10m I made a dipole by cutting a couple of equal 8.5 foot lengths of wire and constructed a “FD style” center insulator from a pair of cable ties taped together.  Used a “composite” feedline – a ladderline drop to a 1:1 unun and a short coax run into the tent.  I had a length of ladder line about 25 feet long so the 10m dipole was up about 23 feet.   At the end of the ladder line at ground level I plugged the ladder line into a 1:1 unun, and ran the last 30 feet or so into the station with coax.  From start to finish this antenna took about 30 minutes to put up, including cutting legs and twisting it all together.

No antenna at all on 80m.  Decided I’d have enough business on 20m & 40m to keep occupied, and figured on sleep rather than a night of 80m T-storm QRN.  😮

Now, about that 40m Vee.  The antenna that would NOT.  Still not certain where the problem was, but it had an issue in one of the feedlines somewhere[update-think one of the legs has broken wire].  Far too much time was wasted raising and lowering the antenna trying to debug the issue.  Lesson1: Always have an alternative.   Lesson2:  Don’t dick around debugging when you have the alternative at hand ready to go.  Lesson3: Save debugging for down time.  Lesson4:  Read Lesson1 and Lesson2 until they really sink in.

Operating:

Once the CQ’s started, there were plenty of QSO’s to log.  Saturday was a bit slow at first, but I got a better rhythm in the evening.  Was tired though, and sacked early, including a 45 minute nap at 5pm in the nice cool breeze that came up.  Also got up early Sunday, 5am-ish.   Sunday morning was quite a bit of fun, right up until my keyer interface died around 11am.  So I finished the event with a bit of lackadaisical SSB, mostly S&P.

Camp:

The Cabelas tent goes up easily.  My only regret is not getting one of the larger sizes.  It has room for setting up a table for the station and also for a cot along the opposite side.  But it is a bit cramped.  Next time I do this I think I will use a screen tent for the station and the tent just for snoozing/bad wx.  Also, the ideal site would allow for the tent to use an overhead spike support and avoid the need for the center pole.

Overall a big win.  Keeping the ants away…..the real challenge!

 

 

2017 FD @ N4GU as AA4NC – Still No Will

The 2017 Field Day is in the bag.  Operated with the group as AA4NC at the farm of N4GU’s XYL.  Showing a surprising lack of judgement for a second year in a row, AA4NC again allowed us to use his call, despite a shoebox full of notices from last year’s operation.  Still No Will….but N4GU, N3ND, N4YDU, N9NB, W4BBT and W4KAZ all on the air.

2016’s as-yet-undocumented FD last year was done as class 2A, while for 2017 we rode with class 3A.  Given the improved conditions on 15m/10m/6m, that was quite a bit less boring than I expected.  Gave N4YDU grief for wanting to run that third station for the high bands, but they were maybe the money bands this year.  Great call on N4YDU’s part.  With so much activity on high bands through the evening and mid-watch, 80m under-performed.  Boooo.  Hoooo.

Stations:

2017 FD - 15m/10m and 6m stations

2017 FD – 15m/10m and 6m stations

2017 FD - The REAL Night Shift

2017 FD – The REAL Night Shift

2017 FD - The "40m station"

2017 FD – The “40m station”

We ran 2 stations on N4GU’s 1kw generator, and ran the third station and VHF stations on deep cycle batteries.  The two stations on generator power were Elecraft K3’s, and the battery station was a Kenwood TS-590.  VHF was run on the Kenwood until N9NB arrived with an Icom 703.  Battery power for the 590 was two deep cycle batteries paralleled and connected to a solar cell, and the 703 was on a single deep cycle battery.

Antennas were a Frankenstein ??ta33M?? tribander for 10/15/20@35′(split via triplexer), an OCF mostly for 40m@34′, an 80m dipole@~45′, a 10/15 fan dipole @ 30′,  a 20m vee dipole at 24′ and a hastily erected 40m dipole @ 40′.  VHF station used a 5 element 6m yagi @24′.  Most of the antennas were strung by late Friday afternoon, leaving time on Saturday morning for testing and a last minute wild hair(the 40m dipole.)

Operating:

Given the strange conditions on Sunday morning, the dipoles played quite well as supplements to the tribander on 15m and 20m, with good signals from New England often better on the dipoles.  The tribander won on stations out to the west of 9-land, and about equal in the middle grounds between.

For my part 15m was the best news on the subject of propagation.  20m and 10m were close behind.  All three bands were very productive.  6m even coughed up QSo’s this year, with 160+ Q’s logged.  The night shift on 80m was a bit sluggish, probably many stations stayed on 20m later than normal.

Something must have worked correctly, event with W4KAZ constantly changing the function key settings on every N1MM computer attached to an HF radio.  Despite KAZ’s  best efforts at disabling the dread “Enter Sends Mode”, almost 3500 Q’s were logged across all of the stations.

WX:

Friday afternoon the WX forecast of rain was quite thankfully incorrect.  Instead there were crystal clear blue skies and a slightly gusty wind.  The wind helped keep the insects at bay, and cooled the crew off a bit.  Saturday morning was overcast, but remained dry right up until a 6pm shift change.  As soon as the new shift sat at the stations, the wind began gusting, enough to slide the camp chairs across the cement floor as if of their own volition.  Enough wind to make ops press down on tables to keep them from tossing radios about like so much flotsam.  The rain soon came in buckets, making the nice covered carport seem like luxury FD accommodations.  The nice 30 minute storm cooled things down and brought the insects from hiding for most of the evening.  Things remained cool enough overnight that a light rain jacket was perfect for both staying warm and fending off the creepy-crawlies.

Food and other:

Many thanks to Mike’s XYL Sherry, who kept us stuffed to the gills over the weekend, and caused disputes to break out over a certain blueberry dump cake.  Also many thanks for allowing us to invade her domain for the weekend and play radio geek.  Good QTH, a good crew of ops to work with, and entirely too much fun.

Red Pitaya SDR as Core of CW Skimmer Station Rebuild.

[Updates, 2018-08-22, also see:  Red Pitaya SDR as Core of CW Skimmer, Part2:  A link to status updates and additional notes going forward]

[Updated 2017-07-11, also see text on my own compatibility issue]

Bob, N6TV has a step by step guide on setting up a Red Pitaya posted to the skimmertalk list in which he documents version compatibility issues he encountered and outlines the steps he needed to follow to get his system functional.  As of this date it seems wise to follow these instructions, or know that by diverging you may encounter issues of your own.  There is also an illustrated how-to guide now available from the folks at hamsci.org.

[Updated 2016-12-23, see text on Compatibility issue]

Recently discovered an interesting,  affordable,  and relatively new product called Red Pitaya, designed as an open source based piece of test equipment.  As a piece of test equipment the Red Pitaya has basic oscilloscope,  spectrum analyzer, and signal generator apps available.  The apps are designed to run as web applications with Red Pitaya board running a custom Linux and acting as a web server.   Currently the apps are quite basic, but useful despite their simplicity.

Possibly more interesting for hams are the SDR receiver and transceiver apps available from Pavel Demin.

With the SDR apps, Pavel has taken this little Red Pitaya board into the areas of interest to many ham ops.  The SDR receiver app has the ability to function with several currently available SDR programs.  The ability to support feeding six channels into CW skimmer server is of particular interest.  There are also transceiver apps which are being used by experimenters to build Red Pitaya based transceivers.

Red Pitaya

The Red Pitaya itself is a board that runs a customized linux OS(their term is ‘ecosystem’) off of an SD memory card.  The board has two RF inputs and two RF outputs for use as the heart of a test system.  5V USB power supply input requires 2A.  The board has a heat sink on the CPU but a small fan helps cooling.  It can connect via ethernet to the network or via a wireless connection.  The OS and apps are downloaded from the Red Pitaya website.   SDR apps are available from both the Red Pitaya site and directly from Pavel Demin’s website.  This little SDR kludge is a viable substitute for the Softrock skimmer system previously being run @W4KAZ.

SDR Uses and v0.96 Compatibility Issue

A couple of issues turned out to be a mix of hardware and software problems.  The largest problem was a software incompatibility issue between the [then]latest OS v0.96 and the SDR software.  This caused problems in the SDR with interference that looks like intermod artifacts.  Too much time was spent here looking for hardware problems before stumbling across the documentation on the issue.  The solution was simple.  It simply required building an SD card with the previous OS version v0.95, and  then configuring(secure password) then re-installing the SDR app.

A couple of the SDR apps available on Pavel’s site originally included an OS that did not allow a persistent password change.  To avoid that security vulnerability, the original SD card here was built with v0.96 of the OS.  As of October 2016, do NOT try to use v0.96 OS with the SDR apps.  V0.95 works with the SDR.  Better to have several SD cards with different OS versions should you need a more recent OS for new apps as they are developed.  [Update 2016-12-23.  Per comment from Pave Demin, the SDR applications have been updated and should now work with v0.96 and v0.97 of the Red Pitaya ecosystem.  Not yet migrated to the updates here in the W4KAZ SDR setup.]

After building the v0.95 system, the SDR app was good to go.   Several different flavors of SDR support are available from Pavel.  The SDR app version that supports CW skimmer server also supports PowerSDR, which has a nice spectrum and waterfall display.

There is not a tremendous amount of information available, as folks are just beginning to explore the possibilities.  PA0AER has an interesting post, with a few findings of his summarized in this table.

PA0AER published test data.

Yeah, -120db floor and 75 db of intermod suppression should work just fine in a CW skimmer application.  

Keep in mind, the softrock system being replaced has about 45db of useful dynamic range as implemented here. Plus we get the bonus of using Red Pitaya as a minimal spectrum analyzer and oscilloscope.  Maybe even a VNA app.

SDR Station With Red Pitaya

First of all, one huge thumbs up to Pavel Demin for his open-source work on the SDR apps.  Outstanding!

The time spent here going in circles chasing my non existent hardware issues was not a waste.  The power supply  was cleaned up with better filtering.  Very nice.  Using the AADE filter design program we also came up with a simple-to-build design for a high pass BCB filter.  This filter optimizes the nulls at 680am and 850am,  and attenuation drops off rapidly above 1Mc the broadcast band.

This BCB filter exhibits low loss on 160m, with the modeled 3db cut off frequency being at about 1.2mhz.  Ordinary C0G/NP0 capacitors are used in its construction, having had acceptable results with that type with the W3LPL design receive only band pass filters.  The result was good with testing on the base station.  The difficult part was finding good leaded C0G/NP0 capacitors in proper values to use for construction.  Through hole components are becoming rare.  NOTE: Be aware – As designed this filter is a short circuit at DC via the inductor at “dipole 12”.

The plot projected by the AADE filter design program above is a best-case prediction.  WPTF, 50kw at 680 and WPTK, 10kw at 850 have transmitters about 3 kilometers and 12 kilometers respectively.  They produced all sorts of intermod in the softrock system.  The BCB design here is tailored to place the largest nulls where they might do the most work in the KAZshack.  Getting the 3db cutoff at 1.2Mc was just to try to keep the losses as low as possible on 160m.  To get an idea of its performance, I plugged it into the station and took S-meter readings on the Kenwood TS-590s.  The BCB filter dropped WPTF at 680 from pinning the S-meter down to just another strong S9+ signal, not even 10 over S9.

S meter comparisons on the TS-590s using the W4KAZ BCB filter and built in attenuator
S meter comparisons on the TS-590s using the W4KAZ BCB filter and built in attenuator

Skimming with Red Pitaya SDR

With the software issues corrected, let the CW skimming begin.  Skimming tests seem to have spot signal levels from Red Pitaya SDR slightly better than those from the Softrock skimmer system.  Full system stress test coming during 2016 SS CW.  The Red Pitaya also seems to be very frequency stable, something that was a minor issue with the softrocks.  When running PowerSDR, comparing Red Pitaya by ear shows it to be a bit less sensitive than the main station rig, a Kenwood ts-590s.

Does it work?

Random selected North American spot counts from days with W4KAZ skimmer station under Red Pitaya
Random selected North American spot counts from days with W4KAZ skimmer station under Red Pitaya

System Reconstruction – Permanent New CW Skimmer

After a good shakedown voyage through Sweepstakes CW, it will be a good time to re-arrange the test Red Pitaya SDR system into a more permanent and compact single system.    One of the dead softrock CPU’s will donate a nice clam shell computer case, and all of the components should fit easily.  The plan is to wall mount the completed system near the shack cable entrance.  The softrock system will be raided for its discrete components, the W3LPL style band pass filters as well as the W7IUV pre amps.  New splitters will be built for the new system to allow for antenna options to change in the future.

Unexplored are some more experimenting to find a proper matching transformer and  Red Pitaya input jumper combinations for the best results.  Some research into the transceiver experimenter comments indicate using a step up transformer is best.  Some have also made mods to the front end that are supposed to boost the sensitivity by lowering the noise floor significantly, from 9 to 12 db.  Currently using a 3:1 cascaded into a 4:1 transformer as step up, with the input attenuation pads bypassed via jumpering on input#1.

Block diagram of likely W4KAZ Red Pitaya SDR CW skimmer system
Block diagram of likely W4KAZ Red Pitaya SDR CW skimmer system

Important Notation[see update]:

If you choose to experiment with Red Pitaya and the SDR apps,  be sure to create your bootable SD card from a compatible OS.   If you do not, you will be very disappointed at the 25db BDR and the interference and low performance you will experience.  Currently, as of 2016-10-28, the 0.96 ecosystem/OS IS NOT COMPATIBLE with the SDR apps from Pavel Demin.  Either use the ecosystems Pavel has or the last archived version 0.95 from Red Pitaya’s archive.  Do NOT TRY SDR with v0.96 OS!  Been there, done that, have a clean power supply and nice BCB filter to show for it.  [Update 2018-12-23.  Per comment from Pave Demin, the SDR applications have been updated and should now work with v0.96 and v0.97 of the Red Pitaya ecosystem.  Migrated to the updates 2017-11-15 here in the W4KAZ SDR setup.]

The Red Pitaya ecosystems come with default root passwords.  Suggest resetting your password ASAP.  Also, at least one of the pre-built ecosystems Pavel provides does not allow a persistent root password change.  I suggest using the 0.95 the current ecosystem from Red Pitaya archive and that the root password be reset to something secure if the Red Pitaya is going to be running on your home network.  With the default root password, your network is open/vulnerable to having a hacked linux system behind your router’s firewall.

Other Useful Red Pitaya SDR links circa 2016-10-28:

PA0AER on a comparison of Red Pitaya to Flex radio, with intermod test result(google translate to english).

FOSDEM 16 program by open source SDR app designer Pavel Demin (Brussels, January 2016)

Red Pitaya as SDR

Red Pitaya Quick Start Guide

Video 2Khz BDR 107 dbm by Yevgeni Kolganov

**

2015 IOTA Recap W4O – Better Late Than Never

Photo of most of the 2015 W4O IOTA station from Okracoke Island.

Most of the 2015 W4O IOTA station from Okracoke Island.

Tri band yagi at 18 feet.

Tri band yagi at 18 feet.

After a lot of foot dragging and interruptions, all of the components required for a 100w battery operation had been acquired at casa W4KAZ in late spring 2015.  The first test run was a 1E Field day operation at home.  But better to put it to use afield.

So N4YDU was game for the field test on Okracoke island for 2015 IOTA.  N4YDU and I operated as W4O from Okracoke Island on the NC outer banks, just south of Hatteras.   Access to Okracoke is by boat, so we booked slots on the ferry out of Swan Quarter for Thursday afternoon.  This worked well, allowing for set up and test operating well before the Saturday start.  Also a nice break for a meal for lunch Friday down in Okracoke village.  QTH of the operation was the NPS campground on Okracoke.

WX Conditions on Thursday were cool with an all day drizzle.  Ugly, but no thunder and lightening, so not terrible.  Set up of camp was delayed until early evening.  Thursday night was warm, damp and still.  Friday morning brought clear skies and an nice cooling breeze out of the north.  The WX was much improved for the rest of the weekend.  Thursdays rain was the harbinger of a very welcome unseasonable cool front, and WX for the bulk of the weekend were very comfortable with much lower than normal temperature and humidity – perfect for field operations.

Radio propagation did not live up to the WX, so there were periods of slow conditions.  A nice breakfast is always good.

Breakfast.

Breakfast.

Solar Power

The solar set up included two 30w solar cells sending power to the charge controller and two deep cycle batteries.  Our solar cells were augmented by the temporary loan of an 85w solar panel by WB8YJF, Jon.  WB8YJF vacations at Okracoke every year at this time, and with his help we had a strong 8A charge current throughout the day Saturday.

 

Solar cells catch a tan

Solar cells out catching a tan on the island. My own small cells in the foreground and WB8YJF’s loaners in the rear.

Batteries and charge station

Batteries and charge station

Having the battery fully charged going into the evening hours was nice.  Rates slowed fairly early, so two days of beachside life had us leaving a few possible qso’s on the table.  Sleep was the better option.

Station

The station consisted of the batteries, feeding power to the Elecraft K2.  Antenna supports consisted of several fiberglass masts.  All of the masts have been modified by drilling holes at the base of each mast section for pins.  Hitch pins are used for the smallest sections, and 2 inch cotter pins are used in the larger sections.  This was faster and more secure than using hose clamps, but it may ultimately weaken the masts over the long term.  That trade-off seems worthwhile for the time saved on deployment and take down.

The W4O station, an Elecraft K2, a couple of tuners and logging laptop

The W4O station, an Elecraft K2, a couple of tuners and logging laptop

The 33 foot fiberglass pole from TheMastCo was used as the center support for a lightweight fan dipole for constructed from 300 ohm twin lead and surplus field wire, covering 40m/20m.  A 22foot fiberglass flag pole combined with most of a 20 ft. Shakespeare wonder pole was used to support an inverted-L for 80m.  Thirteen foot crappie poles were used to get the ends of the dipoles and vertical as high as possible in the limited space offered by two spaces in the campground.  We also deployed a 2 element triband yagi on five sections of surplus military camo mast, at a height of about 18 feet.

Radio conditions were poor, but the WX was unusually good for the NC coast at the end of July.  Great trip and another successful field test of something different.

 

2015 Field Day W4KAZ class 1E

Life’s swirl of events led me to be non-committal about FD with the usual suspects this year.  Probably a good thing, given the way brown stuff keeps making sudden contact with the rotary impeller.  Even the minimal home operation in lieu of a real event was in question as days grew shorter.

So 2015 FD was flying solo in the KazShack.   [Some photos here]  The twist to make it FD was to run the station on emergency power, class 1E.  With enough ’round-too-its’ having been previously cashed in to assemble a portion of the battery set up  desired, the battery op seemed feasible.  Accumulated over the past year are a couple of 30w solar panels, a pair of well-matched deep cycle marine batteries, a decent charge controller, and assorted minor peripherals(cables, connections, etc).  The original plan was to be ready for NC-QSOP earlier in the year.  Brown Stuff vs Rotary Impeller.  Brown Stuff won, no Qso party.

In field day spirit, I also hoisted an “emergency” field portable 40m/20m inv-V off of a fiberglass telescoping mast obtained from “The Mast Company” several years back.  After collecting dust for these years, it occurred to me that it could fill a big unused space on the edge of the ‘wire-farm’, backed up very nicely by the 20m/40m reflectors in their permanent positions.  This worked very well on both bands during FD, showing four or five S-units difference depending on conditions and the direction of the signals.

The 2015 FD Station:

For the event, I relocated the solar panels to be within reach of the feeder cables to the shack. The batteries had been connected to the solar panels for over a month, so they were nicely topped off.  The batteries were brought into the shack, and connections were set up to power the K2 as the load off the controller.  Not willing to go whole-hog QRP, all transmitting was done at intermediate-low power levels, 45w overnight, 75w during daylight.  (Based on actual current draws by the K2 as measured in place). Add a laptop and ready to go.  The antennas were the normal wire farm plus the hasty-install dipole on the fiberglass mast.

The Solar Problem:

Expected to have poor results from the solar panels, as their default location for the shack is only in full sun in the afternoon.  Hoped for a sunny afternoon on Saturday.  No. Such. Luck.  In fact, the WX really sucked.  When the WX didn’t suck, there was lightning and rain.  Zero sunlight.   The panels only produced about .3amps in shade under clouds, instead of their full-sun 2.8amps.  90% reduction.

Solar panels, laid out on a conveniently parked truck

Solar panels, laid out on the conveniently parked truck

Charge controler for solar power

Charge controller for solar power

 

 

 

 

 

 

 

The good news is the batteries seemed up to the challenge on their own.  Battery voltage dropped to 12.3v at its lowest.  The K2 drew only about 11 amps in transmit, and just over 1/3 amp when in receive. If the panels had been in a good full-sun location the charging would probably have kept up with the demands during daylight operating.  Success.  The charger says that 24ah were drawn over 12 hours of operating, with transmitter power at 50w for the 6 hours on Saturday, and 75w for the 6 hours on Sunday.  In full sun the solar cells would probably have kept the batteries topped off until sundown.

The current draw at full transmit power on the K2 is in the 15A ballpark.   Rolling the transmit power back to 65 or 75 watts is a good compromise between output power and current demands, as the current draw is closer to 11amps at 70W.

Actual Operating Condx:

WX conditions cut outs a large chunk of Saturday prime time in the late afternoon/early evening.  So after putzing around for the 1800Z-2000Z hours, did not return to the chair until 0150Z.  Then a decent three hour stretch, alternating between 40m and a few sweeps of the other bands.  A nice long nap and the back in the chair well after sunup Sunday morning.  Not terrible Sunday morning, but not fantastic.

Finished with 532 CW contacts logged and 2128 QSO points.  Not terrible for only about 10 hours of butt-in-chair time.

So the emergency power and emergency antenna set up worked well enough.  A bulk of the QSOs were made on the portable antenna. In the shack the charge controller indicated the station drew a total of 24 amp hours.  The solar cell charging put 9 amp hours back in, not bad given the clouds and shade trees.    That was with the solar cells providing only about half an amp.  In full daylight the charging would have been sufficient, and closer to 3 amps.   The power draw had been conservatively estimated/ball-parked/WildAssedGuessed at a need of about 40 amp hours.

The Renogy charge controller is well worth the minor additional expense.  It senses the voltages from both battery and solar panel, and can charge 12v batteries from 24v solar cells if needed.  It also monitors both load and input currents, as well as the battery charge state.  (Seems to be sold under several different name plates, all seem identical based on advertising specs.)

Overall, very happy with the experiment.

 

 

 

W4KAZ Softrock Based CW Skimmer Station – 05) Si570 Programmable Oscillator for Softrock CWSkimmers – or for “Whatevah”

Note: More links at bottom of page:  This is a simple-to-build Si570 oscillator for use with the Softrock Lite kits for CW skimmer and input to the Reverse Beacon Network.  It uses the Si570 chip and an AtTiny85-20 programmed with the PE0FKO firmware used for the Softrock Ensemble kits.

Currently a programmed ATTiny chip is available separately from K5NWA.  The firmware is available for download, so programming the AtTiny is also an option.  The PE0FKO site also provides the required USB device driver, software, and guidance on using them.  (links)  The Si570 is available from Digikey(digikey part#:336-2518-ND,  manufacturer part:570CAC000141DG).(SiLabs 570CAC000141DG part )

The oscillator itself is pretty simple, and is the bare essential hardware required for re-programming the oscillator for a needed single frequency to use with a Softrock Lite II rx.  It is based on what I saw in the the schematic of the Softrock Ensemble RX, nothing original, just pared down and hijacked from the original Ensemble design.  The Si570 part itself is the bulk of the expense of the oscillator, and the cost of the Si570 chip is almost as much as the Softrock Lite kit itself.    The oscillator signal is fed into the divider through a 10K voltage divider as in the Softrock RX.

So why an Si570 Programmable Oscillator ?

The RX Ensemble kit is a viable alternative expense wise.  It really depends on the intended usage.  Using separate Softrock Lites as single band CW skimmers leads to the choice of a programmable oscillator for customizing the center frequencies, especially for the high bands.  The method used for 20m using the third harmonic seems to result in a decrease in dynamic range.  That results in an increase in false mirror images being reported to RBN by the CW skimmer as actual spots.

Using the Si570, the oscillators can be set at the frequencies needed by the Softrocks, i.e. 4 times the center frequency.  (for 96Khz bandwidth the oscillator would need to be: 20m=56.188, 15m=84.188, and 10m=112.16).   A programmable oscillator also allows switching from 96Khz to 192 Khz bandwidth(20m=56.38,15m=84.38, and 10m=112.38).  Keeping just the bottom half of a 192Khz bandwidth CW skimmer would at a minimum eliminate at least 50% of bad mirror image spots.  There are also likely to be fewer stations CQ’ing below the “.096” section of a band(e.g., most often there is not so much regular CWactivity above 28.096 as there is below).  That is the idea anyway.

The Si570 Programmable Oscillator Prototype:

The first version is deadbugged on a bit of board scrounged from the parts bin.  Not many parts, but a bit more PCB real estate would have been better.  Functional rather than esthetic.  The USB connection is via the usb cable end clipped from an old computer mouse in the parts bin(unlabeled black coil in left of photo).   “Engineer the possible”.

Si570 Programmable Oscillator board for 10m Softrock CW skimmer

Si570 Programmable Oscillator board for 10m Softrock CW skimmer

Testing the original prototype board pictured resulted in three build mistakes to debug:  a missing 5v connection to the ATTiny and the reversal in polarity on both zener diodes across the USB data pins.  These mistakes prevented function without damage to the components.  After correction of the build errors the software was able to function with the Si570 as needed for both programming the oscillator(‘startup’) frequency and running as a stand-alone oscillator.

The Si570 when programmed for 112.36Mc was found to have an actual oscillation at close to 28.090 exactly from the Softrock divider, as measured with TS-590 and Elecraft K2.  This was with the oscillator inserted in-circuit as the Softrock Lite oscillator via a transformer(5 bifilar turns on a type 43 torroid core) and a 2.2k resistor.  The frequency is very consistent and stable when the power is cycled on/off.

Setting the frequency is accomplished using either the USB-Sync program by DG8SAQ or via the test program Si570_USB_test from the QRP2000 project from www.sdr-kits.net.  DGF8SAQ’s program is easiest.

Easy measurement of the actual frequency in place is good enough for initial setting up of the skimmer software. A few KC either way will make little difference in a CW skimmer set-up, as final adjustments were done in CW skimmer software to put the skimmer signals ‘on frequency’.  In this case the CW skimmer center frequency is nearly identical to the Si570 programmed frequency.  That has not been the case with the versions using ordinary crystal oscillators, those having a bit more drift off their nominal value.

A new Softrock Lite II is the 10m test bed, with 15m revision to follow.  These two bands suffer the most from poor dynamic range and false mirror images.  The 15m oscillator also has a nasty tendency to drift with temperature changes.  If the modified softrocks perform as desired it will be time to pair these two bands with the best of the sound cards available.  That will be a separate game of trial and error.  The 20m softrock skimmer may also be retrofit, as using the third harmonic for the softrock center frequencies seems to adversely impact the dynamic range.

Photo of 10m Skimmer

Photo of 10m Skimmer at W4KAZ

As an aside, the first 10m center frequency chosen was 28.060 into a 192Kc bandwidth sound card. Horrible choice, as it was close enough to the 15m harmonic that interference spikes were present on both bands every 900hz.  Resetting the Si570 oscillator to place the center Fo for 10m at 28.080 greatly reduced(but not eliminate) the problem.  Currently set on 28.090 as of 20150414.  More tinkering required, and migrating the 15m Softrock over to an Si570 oscillator may help.

The current Skimmer package for 20m, 15m and 10m. 20m and 15m will likely be re-worked to use Si570 Programmable Oscillators.

The current Skimmer package for 20m, 15m and 10m. 20m and 15m will likely be re-worked to use Si570 Programmable Oscillator.

Si570 Programmable Oscillator UPDATE, 2016-11-08

The Si570 oscillator as described was perfectly usable in this application.  However 10m and 15m performance was was poor on the softrocks, the primary difficulty being a low dynamic range.  This is indicated by mirror images that appear when SNR values on the actual signals were higher than 35dbSNR.

The most useful work around for this problem is to scan at 192Khz sample rate, and only use the lower half of the sample for the CW skimmer.  Using the upper 96kc might be easier, as the center frequency could be set at 28.0Mc and 21.0Mc.  The latter may ulimately be the best approach.  There are unlikely to be any useful signals below the bottom of the bands, and those could be readily discarded as false or otherwise unusable(i.e., out of band).

LINK LIST, Si570 Programmable Oscillator :

  1. W4KAZ Schematic

    Schematic for W4KAZ version of Si570 Programmable Oscillator

    Schematic for W4KAZ version of Si570 Programmable Oscillator

  2. W4KAZ BareBones Parts List (PDF) (HTML with links)
  3. KB9YIG Five Dash softrock products page
  4. K5NWA ATTiny85 page
  5. PE0FKO Firmware page
  6. Document:

 

Skimmer File Extracts Summer of 2014

File extracts for three summer contests from four skimmer stations for May 2014’s CQ WPX and June’s JARL All Asia and ARRL FD.  The files are by skimmer spotting station and are sorted in datetime order.

Spots from K1TTT

Spots from W1NT

Spots from W4KAZ

Spots from KM3T