Created a page of links and several related pages of information on the ongoing construction of the CW Skimmer station at W4KAZ.
Because of the nature of the blog package used for this website, it is easier to save this skimmer related info on ‘pages’ rather than as a “post” because it seems like a project that I’d like to have semi-permanently documented, and have the documentation easily found. Whooop…there it iz….Incomplete, but slowly growing, and probably to be frequently edited in the short term.
After some large amount of initial interest, I quit paying attention to the Softrock. As the years trickled by, the Softrock project kept moving. Lots of projects, mods, versions, and changes.
Here in the present, I had an older Softrock v6.2 sitting on the ‘ToooDooo” batting lineup since around December. It had originally been built as a 9Mhz IF kit, to be used as a panadapter. It was a gift from W3DQ. When I saw the NorCal group had a run of kits available, I ordered a pair. Wish it had been three….
But….it seemed like a good point in time too examine the IF kit, with an eye on re-working it for one of the bands of interest. As it was built, it required only four changes to put it on 40m. The Softrock Lite II kits come with components for building any band from 160m-20m, so the needed crystal was available from one of the kits. The mods took only a few minutes. That got done first.
On a roll, it was time to sift through one of the kits to see what the build was going to take. One thing leads to another….build it! The smell of solder smoke was soon wafting about. The “most difficult” surface mount parts were the first on the plate. As it turns out, these are not the smallest of surface mount parts. An ordinary 15w RatShack iron with a fine tip was sufficient for the task. The difficult part turned ot to be simply identifying the other parts. The numbers on the capacitors were difficult to read, and the color bands on the resistors all look like brown.
Lots of light and magnification? Better, but still some confusion. Most of the issue is progressive myopia, but I had not realized that color-blindness might also be progressive. Not so Fast! In order to get a second opinion, NumberTwoSon took a second look. Even with his 17 year old eyes and 20/13 vision, he also had difficulty. So, after rolling out the ToolTimeTim’s XL 2550Super’scope, the parts were sorted.
After sorting, building was trivial.
Ran first skimmer test on both units on night of May 10th. Its interesting to see the spots a local skimmer finds versus thoses several hundred miles away. A whole project in itself….
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.
(Updated 02/28/2012 de w4kaz)
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.
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.
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. 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. 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.
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. Makes it easy to do with an ordinary hand drill too, since 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 was pulled 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!!
So, 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!
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:
- W0UCE’s accumulation of information on K2Av’s 160m ideas, including the FCP
- Photos from W4KAZ FCP install
- K2AV discussion of the FCP
- Rolling your own FCP isolation transformer, IMPORTANT
- Topband: Where to place a preamp? Switching Beverages?
- Topband: K2AV 160m Folded Counterpoise (FCP), parts and winding for isolation transformer
- Re: Topband: K2AV 160m Folded Counterpoise Antenna (wire suggestions)
- Re: Topband: T-200 vs. T-300
- 2012-05-31, VO1HP FCP install
- DL2OBO FCP page
Put together a WinKeyer2 in a couple of hours two weeks before Field Day. This accessory was added as part of the plan to have the SO2R station capability operational with either USB or serial ports on the logging computer. I chose the version with a serial port, and plan to use it with a serial to USB conversion dongle. In essence, the shack will be forward or backward compatible with the computer hardware, allowing the SO2R to be feasible with whatever crappy piece of computer I have available at any given moment, from an old dos box to brand spanky new.
The keyer kit itself was built with only about 30 minutes of plugging and soldering. The kit was missing a couple of capacitors, but they are common values which I had in the parts box. It took another couple of hours to get the enclosure drilled and nibbled out – including a db9-sized hole in the wrong place. Oops. On hindsight, a simpler plastic enclosure would have been easier.
The finished product worked without any re-work. The WinKeyer2 is the newer release of the serial port version of the kit. I tested the kit out using a USB to serial converter and the “wktest” program available for download on the K1EL site. After a quick test and config with the wktest program, I brought up writelog and tested that. Flawless performance.
Hooking up the paddles was a bit less satisfying. I’m not terribly proficient using paddles and a keyer, and the WinKeyer2 seemed a bit temperamental with my shaky fist. Maybe after more practice it will become easier. But for now, the paddles will be routed through the logikeyer CMOS4, and the paddles will be combined with the computer generated CW from the WinKeyer via a “Y” connector going into the CW input.
I also have the same problem using an MFJ keyer I have on hand. I’m not sure why that is, but so far the Logikeyer and the keyer built into the K2 are the easiest to use of those available.
One quirk I found with the winkeyer(or my understanding thereof) was related to the pot setting for the keyer speed. Starting the programs(either logging program or “wktest”) while the speed pot was set to maximum caused a bit of confusion. To allow computer control of the speed setting, it seemed necessary to disable the speed pot via the software.
Part of the learning curve.
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 DL1IAO, for 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.
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.
W4KAZ SO2R control box
More SO2R box photos
SO2R box schematic PNG Image, PDF file
Audio switching schematic PNG Image, PDF 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.
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.
After building the 80m/160m splitter, it seemed like the signal levels from the K9AY were down a bit, probably from losses in the filters. So after looking around at pre-amps, and procrastinating on buying the Ar2 preamp, I again landed on the W7IUV site.
W7IUV has updated his preamp schematic, and it looked easy enough. Building the project was simple after gathering some suitable parts.
Trying the pre-amp out seemed to show that it was more or less filling the desired role quite well. With the preamp engaged, levels from the K9AY were now on par with signal levels from the transmit antennas on both 160m and 80m. The preamp is installed in the shack just ahead of the band splitter. Noise levels on the RX system were down about two to three S units from the TX antenna in these moderate noise conditions.
During the 160m contest this weekend, the RX system got its chance to proove itself. Noise levels here were moderate – not as quiet as good winter conditions, but not S9+ summertime noise either. The RX antenna with the preamp turned on was always the best choice on weak signals in these conditions. It also necessary to switch the K9AY around a lot – signals were not always best in the expected direction because of higher noise to the north. The southeast direction was dead quiet, but from here in central NC there isn’t much to listen to on 160m to the SSE. The actual compass direction on the SE leg is about 10 degrees south of southeast.
So the short version is that the preamp is an improvement when splitting the RX antenna for two radios.
- Try moving the preamp out to the base of the K9AY, probably in a new K9AY switch box
- Test the RX with the splitter removed, preamp on/off.
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
- Small signal DPDT relay: (For K9AY et al, & 12v control switching)
- TX Antenna switch relays:
- P&B RTB14012F(SPDT, 12A), RTD14012F(SPDT, 16A)
- P&B RT424012F(DPDT), P&B RTE24012F(DPDT)
- AZ755-1C-12DE(SPDT)American Zettler power relay for KK1L & KOxxx projects – AZ755 Data Sheet
- note: The Zettler and P&B DPDT relays are interchangeable(pin layout compatible) if the power ratings are sufficient for your application and both poles of the P&B are tied together and used as an SPDT[i.e., for the KK1L 6×2 switch project]
- Fujitsu, VSB12STB SPDT, 12V, 16A(data sheet marked “to be discontinued” (??replacement??)
- ?? SRUDH-SH-112D1,000 ??
- cd4028: Logic chip for band decoder to drive 2n2222 or 4401
- lm3914( Obsolete?): DL6RAI BevBox – Logic chip for resistance driven switch, drives pnp(part#?)
- Panasonic capacitors(data sheet on 1/1/2010) from NVARC project. Many RF uses. (Digikey part)
- Capacitors: ????CDE DPPM16D1K-F ???? ????TDK CK45-R3AD102K-NR???? ???? Murata DEBB33F102KA3B????
- Toroid King – Iron powder and ferrite toroids, W3NQN toroid kit
- Kelvin – Loads of cool hobby stuff
- Toroid core, type 75 material, Digikey #240-2524-ND (Steward)
- TDK clamp-on ferrite(11mm fits RG-8/RG-11), TDK data sheet, Mouser#810-ZCAT2132-1130BK
- Velleman 8 channel relay card kit, with rs-232 programmed PIC
- McMaster-Carr, coil form edge trim, pn 85085K8 (also bare copper wire, pn 8873K51)
?? more porridge pleeze ??
edited and amended11/02/2009, kaz
Here is a small project that will work along with the K9AY RX antenna, and solve a minor SO2R problem in the KazShack.
Currently theK9AY feedline comes into the KazShack directly to the RX input for one of the transceivers. I wanted to have a way to share the antenna between the two radios without connecting the RX inputs of each rig directly to one another(RF isolation), or manually swapping the feedline between radios.
There are some comments in various places about using the W3LPL RX bandpass filter design to split the bands to multiple destinations. The NCJ article “Distributing Receive Antennas” by K3NA ans W2VJN is a very handy and well explainedreference.
This was also desirable here in the KazShack, which sitsin the shadow of the 50KW WPTF on 680kc broadcast transmitter. Rolling the W3LPL filters was done using some T-50-3 toroids and NP0 and high accuracy monolithic ceramic capacitors from the parts bin. The filter is built dead bug style. Each band is onopposite sides of a singlepiece of copper clad board. Basically, the input is fed to each of the filter banks, and the 160m and 80m bands come out separately, each isolated from the other.
The coils for each band are identical within the band(i.e., L1=L2=L3), so after winding each I used the MFJ-259 to resonate each coil to the same frequencyusing the same capacitor. After soldering everything together, a quick test with the antenna analyzer into a dummy load showed each section to show minimum SWR right where I wanted it. No other tuning was required. Almost too easy.
Left alone at that point, I could feed either radio from either band, but there needs to be a switch of some sort to eliminate the need for swapping coax feeds during the heat of the action. This appeared to be another ideal application of the small signal relays that were also on hand. Using a single DPDT relay, the filter outputs can be switched between the radios with the flip of a switch. A toggle switch mounted on a remote panel is used for convenience . Simple but effective.
The remote panel is a smallsection cut from 1’5 inch(about 38mm) aluminum angle stock. I pre-drilled pilot holes for future use, and installed the switch for the RX antenna splitter, as well as a control for a planned 40m remote antenna switch. The “panel” is then attached to the inside edge of my home brewed fold out station cabinet. The cabinet is filling up fast – not much room for any more equipment in there.
Using the switch is going to make swapping the low bands from one radio to the other a snap. Literally as easy as flipping a switch. The band pass filters will also help isolate the radios from one another in the SO2R environment, as well as reducing the broadcast band harmonics.
There is a bit of signal loss in the filters, but probably not enough to be significant while operating. Hopefully the much lower noise levels on the RX antenna will offset these slight losses. I have not felt a need for an external RX preamplifier before now, but now I am looking at the ARR 1-30. It would be nice to boost the RX signals to parity with the noise on the TX antenna. That might reduce the amount of volume control “riding” needed when looking for the best RX on a contact when toggling between the RX and TX antennas.
Yet another fun little project. It isn’t as much satisfaction as growing an entire rig from scratch, but it is always fun to put a useful bit of home brewed kit into action.
PHOTOS (Full set of photos on external page)
PNG image of schematic for W4KAZ’s version of the “W3LPL RX band pass filters” built as an antenna splitter and switch.
Part 5 of the W4KAZ filter project series discusses filter losses, an idea for getting a very rough S-meter calibration, and trying to estimate the out of pass band attenuation provided by the filters.
The filters do have losses in the pass band. This is known as the insertion loss, and is reported in db. When discussing the pass band, we want the losses to be as low as possible, or approaching 0.0db of loss. The old rule of thumb is for every 3db of loss you are losing about half of your power. So, 100 watts of RF transmitted through a 3db loss component means there is only 50w coming out the other end.
Run that through the loss formula…. db loss = 10*[log(100/50)] = 10*log(2) = 10*.30103 = 3.01db of loss.
Since loss is defined as a ratio of the actual power levels, a simple watt meter and dummy load can be used to measure the losses of a component in db. That gives a nice yardstick for comparision to known commercial filters. The accuracy of the wattmeter is an issue, but part of the game is to compare the values I come up with against values measured with better test equipment. If I ever manage to hook up with one of the guys who are willing to help with that.
The set up to measure the loss in the pass band is simple.
Transmitter–> filter –> watt meter –> dummy load
By replacing the filter with a barrel connector, you can get the baseline power. The watt meter on hand here is not sensitive or accurate enough to use the same technique for measuring signals outside the passband. Not if the filters are working.
Aside: This is also a good way to test a piece of unknown coaxial cable. Rather than rely on an estimate of what the loss should be for a known length of similar cable, it is pretty easy to measure the loss. A quick computation of the loss into db gives you a yardstick on the quality of the cable by comparing it to known losses specified by cable manufacturers.
Anyway…. My set of NVARC filters came in measuring actual losses between 0.6db to 0.8db, and about 1.0db when installed in the integrated switch box. The set of K4VX filters came in at 0.3db to 0.6db.
The problem is that the insertion losses in the pass band tell little about their effectiveness on the 2N or N/2 harmonics.
The only tool available in the KazShack for measuring this type of loss turns out to be the S-meter on the receivers. Receivers are quite good at hearing RF. Kinda their whole purpose in life, right? The new problem is the unknown scale of the S-meter. Is it telling us anything useful?
So: How to calibrate the S-meter?
Okay. I couldn’t solve that one. Is there a possible work-around, or a way to determine the existing calibration of the S-meter?
This puts me off into an area that may eventually turn out to have little real-world validity, but here’s what I came up with. The FT-920 has a three step attenuator pad which is a known quantity. Assuming a simple resistance pad can be easily calculated and implmented by engineers capable of designing such an otherwise comlpetely slick gizmo. For some reason the pad is coincidentally in 6db steps, giving 6,12, and 18db. How convenient.
The unofficial rule of thumb is that an S-unit is supposed to be 6db, with S-9 the 50 microvolt level. So with 18db attenuation, an S-9 signal should be knocked down to S-6. I don’t have a 50? standard, one of countless other things I don’t have, but I am able to generate a signal at various levels. So I decided to use the attenuator pad to calibrate the S-meter markings. Although I may have no idea what level actually causes the meter to read S-9, I CAN use the known values to figure out the values from S-9 down, or S-9 up. I still don’t know the actual signal levels or what signal level corresponds to an S-9 meter reading, but the scale allows measurement of the relative differences in known quantities. In this case, that is exactly what I need.
What this gives me is a round-about way to guess-estimate the effectiveness of the filters where it counts, on the sub harmonics or harmonics. If I know the value of attenuation causing a signal drop from between S-9 to S-2, inserting a filter that causes that same drop will have that amount of attenuation on that frequency.
Nothing is ever THAT easy. S-meters are known far and wide for non-linear behavior, right? Sheesh. But life is full of surprises.
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