Radio W4KAZ

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Rocky rocks softly

After a lot of procrastination, the dormant Softrock v6.2 project became timely.  The job was to convert a Softrock v6.2 from its intended IF usage(IF 9.001?) to something a wee more interesting fer the KazShack main op, namely a 40m Softrock v6.2.  The WB5RVZ pages are the place to go for build information.  A fabulous job of documentation on the many SR permutations.

Turns out, the conversion was fairly simple.  As built, there were only 2 component changes, add the RX enable jumper, and add a wire for the second “ring” line output.  Oh….also change the crystal.  A few resistance and then voltage checks.  Use the K2 as frequency meter to check the crystal oscillator frequency, and its F/4 from the divider. (28.220 and 7.055+/-).

Fired off “Rocky”, VE3NEA’s SDR program.  Putz around with the settings for Rocky and the sound card….Success!  Sweet.

Now the question…….What the heck is this transient!!???!!

 

So…..the project is not quite complete.  There are two full ready to build kits waiting on the sidelines (hat tip to AE5X for noting the availability).  Still need to find a suitable enclosure.  It also seems like inserting isolation transformers in the line-outs will be worth the time, and maybe the cost.  A search on the radio shack site comes up empty for their audio iso xfmr.  Mouser or Digikey.

Job one is a nice shielded enclosure, although there are lots of warnings about being wary of creating ground loops.  Probably put an isolation transformer and front end protector on the inputs.  Separate power source for the SR, and isolation transformer on the lineouts(insulated) to the sound card. Perhaps extra bypass caps on the power supply.

After that is done, maybe the transients will be reduced or eliminated.

Running Rocky on a dual core Pentium D causes the CPU to sometimes spike as high as 7%.  Moving the mouse causes more CPU stress than the SDR software causes.  Interesting.

Gonna be a lot of fun with this toy.  🙂

Many thanks to W3DQ for the original project package.

The Evolution of a 160m Inverted-L with FCP(long version)

Saga of transitioning to K2AV’s FCP(folded counterpoise)

(Updated 02/28/2012 de w4kaz)

(Updated 09/26/2016 de w4kaz, current links & match network schematic)

(Updated 05/31/2018 de w4kaz, add/edit links to newer K2AV FCP page)

TopBand?  Wazzat?

A saga of switching from raised radials to a version of the K2AV FCP for a 160m inverted-L.

The whole idea of operating on 160m started as curiosity.  Before 2005 I had never operated on 160m.  Ever.  I had listened some, but never keyed the transmitter other than to experiment with arcing capacitors and high levels of SWR.  But it generally seemed like it would be fun, so give it a try to find out, right?

After looking at a couple of locations in the yard, it seemed like there just wasn’t enough room to !easily! pull up an inverted-Vee, or other crooked dipole of such unusually large size.  Tall trees out-the-wazooo in the yard, but spaced closely, so it is difficult for long pulls. So there is an emphasis on easy, because it is an important consideration.  Any antenna that is a pain in the ass to maintain is more likely to be out of service at any given moment at the KazShack qth.

There is a great spot for a vertical rise of about 70 feet, so that seemed to be the ticket.  But verticals have their own downside.  Radials – bleh!…Ick!…Ptui!  But any antenna is better than no antenna at all, so that’s where we get sucked into 160m madness.

The first preference was a top loaded “T”, but the useful supports are not arranged in a good pattern for that choice. There was just no way to stretch out the top-hat of the T.

The supports are arranged in such a way that an inverted-L is the logical choice.  So a slightly long inverted L was the winner since it 1) fit into the yard where the trees line up, and 2) lends itself to capacitive matching if made slightly long.  The result was an inv-L  with the vertical section that goes up 70′, then across 40′, and across again in a different direction for another 50′.  Approximately 155′(47m) of wire total length.

That leaves the radials.  Buried radials just were not going to happen.  Far too many tree roots and stone in the back yard, and no grass at all.  What then is the nascent TopBander to do?

The Early years

The first Inv-L install circa 2005 had four elevated radials of equal length, about 37′ each.  All were tied together and loaded via a coil at the base of the antenna.  No chokes, and no decent matching network.   In this incarnation, antenna performance was poor.  Even loud stations were difficult to work.  Heard no DX.  No surprises there.

The first “improvement”  circa 2007 was to add 12 random length radials, a 1.5:1 step down unun(W2FMI design), and a coaxial choke wound from about 70′ of rg-58 wound on a PVC garden pot.  The performance improvement, while not quantifiable was immediately noticeable.  Stations became easier to work on a single call, and I was now able to detect the whispers of DX stations.  A new K9AY for RX was also added to the mix just before these changes to the TX antenna.  It also appeared that the improved TX antenna was now hearing most of what could be heard on the K9AY, although the K9Ay has a much lower noise floor and is usually much easier on the ears.

The Intermediate

Radials were added incrementally from 2007 through mid 2010 until there was a total of about 30.  The original four 37 footers were the longest, and there were another four that were approximately 27 feet long.  Everything else was a mish-mash of random lengths, added in pairs to the available trees in the area.  Somewhere along the line(2008) I also added the capacitors required to get a good match at the base of the antenna, and have a nice low SWR both at the antenna base and at the shack-end of the feed line.  And the nice narrow SWR bandwidth that accompanies such.

Performance of the final well-matched radial version of 2010 seemed to be quite good in comparison to the earliest version.  In 2009 and 2010 it was possible to run stations(low power) in the 160m contests, and Q’s were made more often with the western US, as well as a handful of DX stations.

Before any other changes were made, I took some signal strength measurements in late 2011 using the K2 as field-strength meter, with the FT-920 as transmitter.  The test configuration was 1) transmit full power from the FT-920 on the TX antenna at its lowest SWR point, 2)RX on the K2, using a dummy load at the end of a 7 foot jumper cable.  dummy load hanging off edge of desk.  K2 attenuator on, rf gain at max.

Using that configuration:

  • 100w into the transmit antenna produces S-5 on K2 S-meter
  • 100w into separate dummy load produces audible S-zero on K2 S-meter

As poor as it is, that reading is the best actual measurement available, from what in my opinion was the best of the radial configurations.  Taken in early December 2011.

Decision Time

In 2009-2010, K2AV began discussing an idea he had for solving the small-lot-on-160m problem.  Based on his modeling and studies of ground losses, he reasoned that a single counterpoise might be a solution that would work for space limited locations.  He determined that a counterpoise that was 5/16th wavelengths might show useful current cancellations if it were strategically folded, to help with the problem of ground losses.  So evolved the “5/16th wave folded counterpoise”, now being generally referred to as  “516 FCP” or just as “an FCP” . The idea seemed to have a lot of merit, but being a serial procrastinator it took some time for me to get off my hindquarters and make the changes to try it out.

In early 2011, K2AV gave me one of his isolation transformers, as well as an inductor.  Their implementations of the FCP at K2AV’s and W0UCE’s qth required  additional inductance for matching(hence the inductor). They also discovered that the isolation transformer was a necessity to obtain good field strength results.  The transformer design is beefy enough to handle their high power operations.   The design of the FCP has gone through some evolutions/refinements, and the design K2Av is recommending was originally field tested at his own qth in the 2011 CQ160m CW contest with low power, and with excellent results.

K2AV style FCP System Installed

My own original intent was to install his isolation transformer into my original system and transition to the FCP.  Curiosity compels me to wonder what sort of improvement the isolation transformer might have provided on its own in the old system.  That test never happened, but it is really just a matter of curiosity.  It would still be good to know if the transformer would have made an improvement in signal with the radial jumble.  I expect the choking on the radial system was less than ideal,  far less than what was necessary, and the system probably was subject to higher losses because of that. That transition never happened, so I missed having the new system ready for ARRL DX. Impatience won out when an opportunity to do the work came up.

In the week after ARRL DX, the radials/coil were removed and K2AV’s folded counterpoise and isolation transformer were added to the antenna.  [NEW link: K2AV FCP home page]  A new junction box was built to house the isolation transformer and matching network.  K2AV came by with his analyzer, and we spent a morning giving the system a look-see.  As it turns out, the same value of matching capacitors were suitable for use without modification, and the inductor was not required because my inv-L is long.  Matching the system was as simple as adding capacitance until a match was found.  A large value air variable could be used to find the required match in less than five minutes, then replaced with capacitors suitable for handling the currents.

My own matching network is a group of HV ceramic caps in parallel[Obsolete, probably unavailable, 2016/09/25].  These are mounted on a board that allows switching some of the capacitance out to move the resonance up the band.  The switch board will also allow switching to a different vertical element, but that feature won’t be useful without also switching the FCP.  The FCP is a mono-band solution.

Schematic for W4KAZ 160m inverted L with K2AV FCP

Schematic for W4KAZ 160m inverted L with K2AV FCP

Picture of W4KAZ 160m junction box

Picture of W4KAZ 160m matching network and transformer junction box in use with 155 foot long inverted L and K2AV FCP

The Present….So, What of it?

The system now up is the same/original inverted-l vertical section with the K2AV folded counterpoise and isolation transformer in place of the prior elevated radial jumble.  What happened?

Using the K2 as field strength meter again, and using the exact same conditions as described above(sense antenna dummy load hanging from desk on 7 foot jumper):

  • 20w into the antenna from FT-920 now registers S5 on K2 S-meter
  • 40w into the antenna from FT-920 now registers S5 plus one bar on K2 S-meter
  • 60w into the antenna from FT-920 now registers S5 plus two bars K2 S-meter
  • 100w into the antenna from FT-920 now registers S9 (S5 plus three bars)
  • 100w into separate dummy load produces audible S-zero on K2

The S-meter on this K2 is not calibrated in real world db, but even without knowing exact values the signal is obviously stronger than it was with the previous TX antenna system.  Yes, that’s in the near field, but still it is encouraging.

The first field test was during 2011 Stew Perry.  Anecdotally, I was very happy with antenna performance.  It really seemed like I was louder, and it seemed I got fewer requests for fills.  But the time for a full effort wasn’t there, so there is just a limited amount of data.  Not too shabby for just three hours of operating.

A better sample was taken during the 2012 CQ 160m CW.  (And here.)  A total of 20 hours was operated. Terrible propagation conditions.   The first 6 or so hours were very good compared to previous 160m contests.  20 total hours of operation produced 593 QSO’s.  Even with terrible conditions, I was able to work a couple of EU stations.  Low Power.  Not as good as K2AV in 2011, but one hell of a lot better than I anticipated, especially in poor conditions.  K2AV is also a much better CW op, so I doubt I’ll ever be able to hit that 925 Q milestone.

So I’m pretty happy with the current system incorporating both the FCP and isolation transformer.  Many thanks to K2AV!

W4KAZ Construction Variance Notes

In implementing the FCP design at the KazShack, I made a few variances from the recommendations.

The FCP itself is constructed of stranded 14ga hardware store THHN.  I like the flexibility of the wire, the sturdy insulation, and most important, I have several rolls of it already bought and paid for.

The FCP insulators were cut from an unused piece of PVC electrical conduit.  That was also what happened to be at hand in the form of spreaders from an experiment with hex-beams.  From the length of PVC available for the job, I cut 16 spacers of 6 inches length(~150mm).  Each was drilled through three times, a hole in the center, and one about .5 inches from each end.  On the leg with two wires, the spacing is about 5 inches(125mm), while on the leg with three conductors the spacing is only ~2.5 inches(~60mm).  The holes are intentionally mis-aligned or drilled at offset angles.    That allows the wire  itself to place tension on the spreader to keep the spreaders in place.  This method makes it easy to do with an ordinary hand drill – being crooked is an advantage.  🙂   The mis-alignment alone is not enough to keep the spreaders from sliding, so they are also wrapped with vinyl cable ties as needed.  The distance between each spacer works out to about 4 feet(~1.3m).  Vinyl cable ties are also used as spacers  at the midpoint between each PVC spacer.

Measuring and threading the wire was the most time consuming part of the FCP construction.  Because all of the separators are of equal size and drilled the same, the side of the FCP with three conductors is more closely spaced than the side with two.  This made mechanical construction very easy, the FCP is taut and sturdy, and did not seem to have any adverse effects on performance.

The transformer and matching network is installed in a nice hamfest/surplus telco box, about 8x8x4.  This is a nice weather tight enclosure.  The transformer is exact to K2AV specs(by definition – it was wound by K2AV his-self!).  The matching network of switched parallel caps is scavenged from the old weather enclosure(a sealed PVC pipe) and re-used in the new junction box.  These components fit well enough, but there would not have been space to house the additional toroidal inductor had it been needed.

Besides the apparent  signal improvements over the rejected-random-raised-radial-rambling-razzledazzle, the FCP itself has other very practical mechanical merits and advantages over raised radials.

  • The folded counterpoise is simple to build.
  • The FCP is relatively small, 32′ per side(64′ total length)
  • The FCP is a LOT easier to deploy than 30 elevated radials, or burying a dense radial mat
  • The FCP lends itself to following contours, and models well when the FCP is not perfectly straight
  • The FCP will require a lot less maintenance.  The odds of falling branches breaking the FCP here at the home QTH are lower by a factor of 15. (2 legs of FCP vs 30+ radials in 30+ directions, all below branch shedding trees)
  • all of the above…..  !! yipeee!!
Bottom Line…..

But Kaz, is it equivalent to a full size vertical with a dense mat of radials?  Probably not, but there is absolutely zero chance that sort of system can ever be installed at this QTH, so the point is moot.  Do I care?  Nope, it “works”, and it “works” better than it’s predecessor 160m antenna systems at this QTH.  Very possible that improvement is just testimony to the poor performance of the prior system. But better is “better”.  Is it snake oil?  Probably not, at least not according to the CW skimmer robots and the results K2AV has had with his system, and more important, my own field testing during the CQ160m contest.

At this point, my only regret is an academic point – not having run the test of inserting the isolation transformer into the old system with the radial-jumble.   The sharp tuning of most 160m antennas suggests that common mode currents will often be a problem as one tunes away from the antenna’s resonance and the reactance increases.    How much benefit is gained from either the isolation transformer or the FCP individually is unknown(to me), but still of both practical and academic interest. I’d really like to know if the old system would have been improved with the isolation transformer installed. Still of interest, but not enough for me to spend time hanging the radials back up again!  😉   Together, the FCP and transformer seem to do a damn fine job here.  Certainly the best system that has been active in this location.

What next?  FCP phased verticals…..FCP foursquares…..FCP parasitic arrays….. MANY possibilities –  if only I had the room to do it!

References:

Until such time as K2AV publishes on the subject,  the available references are the basic instructions and a few message threads on the TopBand mail list on pertinent topics:

  1. K2AV NCJ article “The FCP: A 160 Meter Counterpoise for a Postage-Stamp Lot “
  2. W0UCE’s accumulation of information on K2Av’s 160m ideas, including the FCP
  3. Photos from W4KAZ FCP install
  4. K2AV discussion of the FCP
  5. Rolling your own FCP isolation transformer, IMPORTANT
  6. Topband: Where to place a preamp? Switching Beverages?
  7. Topband: K2AV 160m Folded Counterpoise (FCP), parts and winding for isolation transformer
  8. Re: Topband: K2AV 160m Folded Counterpoise Antenna (wire suggestions)
  9. Re: Topband: T-200 vs. T-300
  10. 2012-05-31, VO1HP FCP install
  11. Balun Designs commercially available FCP transformer

Other links:

  1. W1UJ : http://w1uj.net/FCP/
  2. KY6R : https://ky6r.wordpress.com/2015/04/27/160m-fcp/
  3. IV3PRK(FCP @ HC1PF) : http://www.iv3prk.it/hc1pf-tx-antenna.htm
  4. DL0WH : http://dl0wh.de/80m-vertikal-mit-gefaltetem-gegengewicht-nach-k2av/
  5. DM9EE: http://www.dm9ee.de/FCP_info.html
  6. W8TN : https://w8tn.blogspot.com/2012/07/building-k2av-fcp-160-m-antenna.html
  7. WB5NHL : http://oldcyberdude.com/sample-page/antennas/160m-folded-counterpoise?
  8. ?
  9. ?

 

2012 CQ 160m CW Pre-game

Getting the last minute woolgathering in before the contest begins.

Made a last-minute antenna mod to the Inv-L with K2AV FCP.  The antenna matching network has been ready for switching out matching capacitors for over a year.  The missing piece has been a control box and control cable to the feedpoint.  After a bit of consideration of solving this issue before the contest, the brain caught up and realized an interim solution was already in place.

When the Sixpak was added to the antenna system a couple of years back, the existing seven position switch was pressed into ‘temporary’ service as an A/B switch for a pair of 40m dipoles.  But they occupy positions 1 & 2 on the switch.

So why not use the other switch positions to serve double duty?  The switch is about ten feet from the base of the 160m antenna, so its a short run of control cable versus the 80 run needed back to the shack.

So as a quick and dirty solution, I hacked together a plug to mate to the switch control line.  Just plug the 160m switch into the control cable for the seven position switch.

Presto-change-o.  Now I can move the best match on 160m from 1820 up to 1845.  Sufficient for a CW contest, although 1855 would be ideal.  More tweaking needed, but better.

Goals for the weekend are more or less to lay down a good set of spots into the Reverse Beacon Network.  No real QSO goals.  Try to maximize time spent running, and try to do it over two nights.

C U L   de w4kaz

2011 Summer Review – Functional, But Maybe Not Esthetic

One of the things that kept me away from the keyboard was a woodwork project idea.

Several years back, I saw a design for a compact kitchen/breakfast table.  The tabletop folded over to convert the table into a bench.  The basic idea was used to build two outdoor tables of similar design.  They are very functional, but a bit heavy.  One is in daily use as a catch all work table.  The other slightly larger table is on the backyard patio and is used with the tabletop grill.

The eldest son moved to an off campus apartment which has a large deck.  It seemed like a good place for a similar table.  So it was time to pencil out a new design that I could put together for an updated “new and improved” version. Several years of use had made some of the shortcomings of the original tables obvious.  The “new” ideas are that:  1) it needed to fit into the car for transport, and 2) should be made of lighter weight materials to generally make it easier to move around.  This is what popped out…….

Picnic Table/Bench

First attempt at picnic table bench

Not a terribly good photo, but there are a few more coming.

The table has four components: 2 sides, the top, and the bench.  The sides are simply bolted to the bench with 1/4 inch carriage bolts, while the top rests on top of the top arms of the side pieces.  The top is simply pinned into place using 1/4 inch J bolts.  The top itself is formed from boards attached to ribs with deck screws, all countersunk from below keeping the tabletop unblemished.   The table top hinges over on the rear pair of J-bolts to become the backrest for the bench.  Pictures are better….

Picnic table with top folded back as bench.

Picnic table with top folded back as bench.

The materials used are all pressure treated pine lumber.  To give the surfaces a bit of a protective finish, the table top got four or five coats of good old-fashioned pure tung oil, which incidentally has become difficult to find.  I like tung oil – it is more resistant to mold and mildew, so is better for an outdoor application than boiled linseed oil, and I expect it to hold up in the mountain UV sunlight a lot better than a polyurethane.  After its dried, tung oil is also resistant to alcohol and related solvents.  Good stuff.  I suppose it has fallen from favor because of the rise in popularity of the polyurethanes, and the substitution of the less expensive boiled linseed oil finishes.  It was also a bit of an experiment, as none of the other normal finishes are worth a flying-*#%^ on pressure treated lumber, whereas tung oil does a better job on this material and is non-toxic, unlike oils designed for treating pressure treated decks.

So the table top and bench have a nice hand buffed tung oil finish.  Its difficult to tell in these photos, but that experiment was proven to be effective.

The back of the bench

The back of the bench

As it turns out, the selection of pressure treated that happened to be in the bin at the big-box-lumber-retailer included several nice heart-pine crosscuts, which had nice colored grain detail.  The coloration was enhanced by the oil finish.  It really looks a lot better than I expected.  Almost kept this one and made a second table for NumberOneSon.  😮

side view of bench attachment to side arms

side view of bench attachment to side arms

Inside/underside view of bench attachment to side arm

Inside/underside view of bench attachment to side arm

The problem areas in the design relate to the hinging of the table top and its use as a seat back.  The sides of the table are made from deck ballusters.  I’ve found that these are generally cut from knot free sections of clear even-grained wood, and are quite strong.  Also relatively inexpensive.  So the side sections are held together with deck screws and waterproof polyurethane exterior construction adhesive.  The top rail may not be strong enough for the hinge, and may eventually need a re-inforcement of steel or aluminum added.

Also, the original benches had wider sides, which served to “stop” the  bench top fold over at just over 90 degree seat back angle.  Solving that problem on this new bench did not occur to me until it became clear the sides here will allow the top to hinge over well past a comfortable seat-back angle.  So the kludge to remedy that design flaw was a simple chunk of balluster attached at angle on the inside of the sides.  It helps add rigidity to the sides as well as acting as a bumper for the table top when hinged over as a seat.

 

Side view of table with top hinged over for use as bench

Side view of table with top hinged over for use as bench

Just right for soaking up a bit of mountain sunshine – and hopefully the moonshine won’t eat away the finish.

This Should Be Obvious

Sometimes common sense is everything but common.  Just never can find the right adapters when hooking everything back together.

Case in point: It is a lot easier to use 1/8th(3.5mm) stereo plugs, and use an adapter to go up in size to 1/4 inch.   Going from large to small just adds stress to the connections.  The smaller size is also becoming the more commonly used jack on gear as the gear itself becomes smaller.  Soldering the teensy connectors is more of a PITA, but such is life.

Just as soon chop all of the paddle and keyer plugs now – almost all of the shack radio gear has 1/8th jacks now.  But the peripherals seem to all still have 1/4 plugs.

Another fun fact: It’s easier to use all stereo connectors than a mix of stereo and mono.  A stereo plug can be wired tip and shell for mono usage, but a mono plug is worthless when you need stereo.   So to hell with mono 1/8th and 1/4 audio connectors.  They are banished forevermore from the KazShack.

Soldering Tip: When soldering RCA, 1/8th or 1/4 plugs, it is worthwhile heat sinking the connector, especially with low-quality connectors.  The easiest way is to just plug them into a jack.  That seems to provide enough sinking, unless you really try to cook them.  This seems to really be helpful with RCA connections, where the center pin will sometimes drift if the connector is overheated.  Using an RCA barrel as heat sink allows a melted connection to re-solidify correctly aligned.  Good to go, unless it shorted when overcooked.

Interesting Products

I built the Idiom Press cmos-IV Logikeyer a couple of years back, and it is the best keyer I have owned.  Easy to build kit too.  N4YDU has recently added one to his collection too.  A great external keyer, and good for field operations.

Idiom Press has two new products that look very interesting, a stand-alone voice keyer, and an outboard RF speech processor.  The voice keyer looks like it is exactly what I wanted – perfect for Field Day or the IOTA expedition.  Also useful if routing audio from the computer is an issue.

The speech processor is yet not priced on the web-site.  That’s a good thing, since I’m not ready to BUY yet.  Both products would make a difference for low power operating/field day.

Recent station derangements have re-introduce an RFI issue onto the K2.  This is a bit of a puzzle, but I expect to find a case of “ID-ten-T” is involved.  Just not yet sure where.  Looking at the setup fresh may help, but I see one link in the chain I want to meddle with right away.  I’d eventually like the audio transformers in the SO2R switch box at each of the radio lines. That would keep all three audio devices(computer, radio1, radio 2) isolated – currently not the case.

A mini experiment is in the works there, by isolating only the computer audio before it enters the SO2R switch box.  I expect a transformer at that point in the stream to have no effect on the problem, but if it works I may make no other changes.

Inverted-L Matching

The 160 Inverted-L is about 160 feet of wire.  To get a good match there is a series capacitor in line with the wire.  The bandwidth for any useful value of capacitance is about 40kc.  The object is to use a set of relays to switch in or out additional capacitors.  That will allow the antenna to be tunable across most of the band – from 1800kc to 1930kc.  There is also a 1.5:1 unun at the feed point, followed by a coax cable choke.  This lowers the SWR to a very nice 1.1:1 over the useful range.  The rig is very happy at resonance, and a good match will be a dial click away.

Currently the capacitance in the system gives a nice 1:1 SWR at 1825kc.  Using the autotuners, either radio [K2, FT-920] can work from 1800 to 1875.  The goal is to be able to turn off the tuners and feed the antenna directly.  Maybe I’ll pick up a few extra QSO’s with a good match on the antenna end of the feedline.

After several other projects using relays and the 3kv Panasonic capacitors for the band pass filters, enough extra parts are in the parts bin to make it happen.  So, why wait?

A handy nearby line previously shot into a nearby biological antenna support provides an opportunity for expansion.  The line seems well placed to add an INV-L element for 80m.  One additional relay for switching bands.  Judicious choices for the capacitance values may allow the sharing the capacitor banks for either antenna.  Being able to cover the CW segments is most important, so the minimum value used would ideally resonate each wire near the bottom of either band.  Hmmmmm.  Time to pull the 80m wire up and start tinkering.

Notes On SSB RFI In Homebrew SO2R Box

Chasing down the RFI caused by inserting all of the home-brewed SO2R components into the station set up was a useful hands-on experiment. Annoying, but certainly educational.  I verged on ordering the ARRL RFI tome, but now the thing is fixed, owning the reference seems less urgent.  Might be worth reading though…..probably quicker than re-inventing each technique personally.

To start, the shack layout resulted in a few less than ideal situations. Both radios are side-by-side, separated by about 300mm. The computer that logs and controls both radios is on a rolling cart normally kept close to the station desk. The computer was also being introduced into the audio chain as the DVK, and I was also working towards routing the mic audio through the sound card full time. The cramped space on the desk is further reduced by the antenna switching controls and an antenna tuner. One set of bandpass filters is built into a relatively large computer case, and that occupies much of the top shelf.

No RF problems were noticed on CW, but on SSB the audio was terrible, and I got many reports to that effect. Apologies to those who were exposed to it.

The unshielded plastic enclosures used may have contributed to the problem, but so far most of the trouble has been corrected by applying the normal RFI kludge, clamp on ferrites.  Shielded enclosures probably can’t make the problem any WORSE though.

The audio stream for the Yaesu FT-920 was relatively easy to clear up. Three or four turns of cable through one or two ferrites seemed to do the trick. The K2 was more difficult to tame, but it was also the furthest from the computer. I expect that the longer audio cables needed to reach the K2 made better antennas for picking up the stray RF. The cables used are a mix of CAT-5 and shielded RCA audio cables. The CAT-5 cables carried the mic audio, PTT and CW from the So2R box to either radio.

In addition to the ferrites, I also routed the audio from the computer through an isolation transformer. That step alone almost completely solved issues with the FT-920.  Using a separate power supply for the SO2R box resulted in acceptable audio –  better, but not BEST.

Two of the issues were a big surprise – and I only discovered them as RFI ingress points because I reached the point where I was determined to cover every base.  The separate power supply was an issue that was unexpected, but should not have been.  NT4D has made that point to me several times over the years.  Unfortunately good advice often falls on deaf ears.  I have heard the gospel now….

The one that I really dd not expect was that the PTT line might be an RFI source.  It became obvious this was a source when I methodically disconnected various cables on the K2 end of the chain.  Low and behold, once the PTT line was disconnected from the SO2R box – no more RFI.

I may now re-visit the entire chain, substituting a better quality cable to see if there is any difference or if fewer ferrites might be required.  It took three ferrites with about five turns on each to subdue the RFI ingress from the PTT line.

Here’s a summary of the mitigation steps taken to end the RFI issues.

Problem #1:
Power supply – One source of RFI problems was sharing the radio power supply with the SO2R box. Putting the SO2R box on a separate wall wart helped a lot.

Problem #2:
SO2R box cabling. Because of the shack layout, the SO2R cables are all pretty long. Putting ferrites on all cables more or less solved the problem with the FT-920. Still had RFI on the K2.

Problem #3:
Added .01 bypass caps across all of the relay coils and DC connections in all switch boxes.

Problem #4:
Didn’t really have ferrites on ALL of the cables. I really didn’t expect the PTT line to be an RFI issue, but solving the RFI problem on the K2 required ferrites on both ends of the PTT line(at the radio mike jack, and at the relay output in the SO2R box), as well as on the foot switch itself(at the SO2R box). While I was at it I added ferrites to the DC power cords too. It took three ferrites right at the mike jack on the radio end, so that may have been the real source of ingress.

Problem #5: Add isolation transformer in line with audio from the computer before going into the SO2R box.  Putting the transformer at the input to the SO2R box was an arbitrary choice – I don’t know if its location in the audio stream is of great consequence in mitigating the RFI.  Its placement there ensured only one transformer was required, since all audio is routed through that location, not being split until later in the SO2R box.  The location was convenient – perhaps not ideal.

Caveat: It is possible I also did something else inadvertently which helped solve the problem, but after a couple of weeks of head scratching and trial and error, I can say that UNdoing any one of #1 thru #5 will re-introduce some amount of RFI.

The problem with the PTT line really has me perplexed, but I guess it is in close proximity to the audio cable at the radio mike jack, so any RF on the PTT line is probably getting into the audio there.

After all of the trial and error, my impulse in the future will be to add ferrites on all control cables on both ends, and immediately after they enter/exit each device.

Home Brew SO2R Box

This home brew SO2R controller project follows the “old-n-busted” theory, and is based on the design by N6BV in the ARRL Handbook, as well as some input from K4QPL. In summary, it is built around the use of an LPT port for computer control of the CW, PTT, Radio A/B, and band data. As previously outlined, the LPT port is less expensive and easier to accommodate – even if obsolete.  Hence “old-n-busted”.  I expect to be able to bridge the gap to USB at some point by adding a K1EL WinKeyer, and the Piexx SO2Rxlat dongle.

The rig control is still accomplished via a serial port for each radio. The LPT parallel port is used for PTT, CW, transmit focus, and band data for one radio. The K2 band data is a separate option not installed in my K2[another void the Piexx SO2Rxlat dongle will solve].

As it stands now the only parts missing for a conversion to USB device control are the WinKeyer and SO2Rxlat devices. Everything else in the SO2R control chain is home brew.

There are several resources available that block diagram the components needed inside the shack for SO2R[e.g.,see DL1IAOfor the W5XD SO2r Box].   For ease of use and construction, the heart of the SO2R box breaks down into four logical units which were built into three separate boxes.

Band Decoder: One of the peripheral boxes will provide automated band switching driven by the logging program[or directly from a radio] by acting as the band decoder.  Most logging programs provide band data in the “BCD” format, and Yaesu radios provide that format via their hardware dedicated band data outputs.  The binary coded band data make the design of the decoder relatively simple.  In hindsight, it seems like a good idea to expand this component’s abilities by using a set of relays to provide for either positive or sinking switching.  This is a consideration for driving band pass switches or antenna switches, and is also a design factor for home brewing those components.


Inside view of homebre band decoder

The internal view of the band decoder


More band decoder photos.

Band decoder schematic. PNG Image, PDF file

For those looking for an inexpensive band decoder solution, the Unified Microsystems  band decoder looks like a real bargain and could easily be incorporated into a home brew design. To build a band decoder, it is probably better to start off with the Unified Micro unit and build the support hardware around it.

Audio Switch: The second is a simple peripheral to the main SO2R box is a simple remote switch. This device itself is simple, yet it really makes the SO2R a lot easier.  This device was subdivided into two physical component parts.  The actual relay board that switches the audio was built on its own small pc board and mounted within the SO2R box.  The user controls are mounted in a small project box.  The small box sits just above the keyboard on the desktop.

For my own preferences, it seemed better to have one small “remote” user control box for switching in the heat of battle. The remote has a rotary switch to control the headphone audio, and it can choose either radio individually, stereo with one in each ear, stereo with left and right reversed, or it can be set to have the audio follow the transmit focus.  It also has a momentary contact switch for each channel, which can be used in stereo mode to listen to either channel for as long as the switch is depressed. The remote switch control is connected via a Cat-5 cable to the SO2R control box.  The control box and its rats nest of wiring can be placed away from the station controls.

Remote: The momentary contact switch feature will soon be enhanced to correct an original construction oversight.  Parallel connections for the momentary contact switches will be added to allow using a footswitch.  That will provide hands-free audio switching when in stereo mode.  That is important, as I need the hands free to type and deal with CW and radio tuning. Hat tip to K4QPL for the idea.

Remote locating allows both the main SO2R box and the band decoder to be located away from the other major components in the station.  That highlights the single caveat I experienced – RFI on SSB.  After experiencing RFI problems during ARRL SS SSB, both of these  units still need some attention paid to choking RF on the interconnects.  Re-locating them a bit further from the RF hot spots and coax connections should also help with the RFI.  Judicious and liberal use of clamp on RFI chokes seems to abate the problem.

For some reason, the K2 seemed more susceptible to RFI than the Yaesu FT-920.  The RFI source there turned out to be on the PTT line.  A combination of ferrites and a diode in the PTT line finally tamed that hotspot.  Note:  in the PTT line, the PTT hot is at the radio’s mike connector, and it really didn’t sink into the thick head right away.


The completed SO2R control box

W4KAZ SO2R control box


More SO2R box photos

SO2R box schematic  PNG ImagePDF file

Audio switching schematic  PNG ImagePDF file

SO2R Box: The guts of the system all reside in the main SO2R box.  It has inputs for headphone audio from each radio, CW inputs, PTT inputs, and microphone audio inputs.  There is also an LPT Db-25 input for connection to the computer.  The set up is designed to receive control input from the computer LPT port to drive some of the switching and provide band data.

The main box contains two separate components. Two small perf boards were used to simplify construction.  One board contains switching for the headphone audio.  The other board handles switching for the CW, PTT, focus control, and microphone audio.  The audio is normally switched via the switch remote, but it can also be slaved to follow the logging program’s transmit focus and be controlled from the main SO2R board.

Future Migration to USB:

In order to migrate to a logging computer with USB ports, it should be a minor change to replace the LPT cable with a USB connection via the Piexx SO2Rxlat device.  By making the components LPT port compliant, the SO2R capability can also remain backward compatible with an older computer that has no USB support, running Writelog.  Just in case the only option is an ancient junker from someones junk bin.  The SO2RXlat will also provide band data for both radios via a single LPT DB-25 connector.

Postmortem:

The total cost in parts was not large.  The 4401 NPN transistors, relays, connectors, bypass caps and diodes were all generic ‘project part’ items I have been accumulating over the past several years. I have gravitated towards using RCA connectors because of the availability of inexpensive sheilded RCA cables and the low cost of the connectors. The CD2048 IC for the band decoder was a dedicated purchase, and were around $1.98 USD.  The amount of time put into construction, the biggest real expense, amounted to about 15 total hours, spread over a long period in several hour long increments.  I spent more time debugging the RFI issues.

The RFI is probably partly due to using plastic enclosures, but these enclosures were easy to come by.  In hindsight I would add ferrite beads on to all interconnects inside the boxes.  The ferrites on the interconnect cables create a bit of additional clutter and impede quick wire pulls. Kludgy.

The remote switch has since been modified to add a jack for an external switch to concentrate both channels on either the left or right radio.  This will allow for use of a foot switch and will allow hands-free audio switching.

Small Parts List

Some suitable and inexpensive parts for future projects. A continuing aggregated list of Stuff I Use To Play Radio.

last update 2010-04-22, w4kaz