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Sometimes procrastination pays off. On W7IUV’s web site, he has a link to his “W7IUV preamp”. The document was revised a few months ago, and it includes schematics and parts lists for both versions, as well as a general discussion on the preamp. It appears that no suitable surface mount parts were found to replace the transistor. Not like I want to play with surface mount components anyway. Some suitable and inexpensive parts for future projects. A continuing aggregated list of Stuff I Use To Play Radio.
Got a chance to work on the matching network for the inverted-L, adding in series capacitance, a choke, and balun. This gave me a good match at about 1840, and the SWR was decent from 1815 up to about 1860. The results seemed to be an improvement in the chances of being heard by most stations. That’s with just 100w. Decent results, given the low power and inefficient antenna. Got in three really nice runs. The first was disrupted by another station sliding in. That was annoying, because the 10 minute rate was up over 100. After I moved, I settled into a nice 40 minute run that finally pooped out of its own. There was only a limited amount of time available, so the periods from 2300 local “until” were chosen from both evenings. There seemed a whole lot less activity on Saturday evening. Logged about 3 hours and 130 Q’s Friday night but only 2 hours and 70 Q’s Saturday. Found KH6ZM working a big pile-up on Friday night. Listened to that for a while, but I only heard him work a couple of east coast stations. The west coast and mid-west were pretty thick, so I didn’t waste time. Tuning up the band I found HI3 calling with no pile-up. Also worked a G3 and a few Caribbean stations. The K9AY made the difference on several Q’s. The noise wasn’t bad, but There were a couple of relatively weak stations that really peaked on the K9AY but were in the noise floor and not copiable on the inverted-L. Armchair copy on the K9AY. Interesting. Many others were easier copy on the xmit antenna. Also interesting. The matching network is another great application for a relay box, so I can have a good match at selected parts of the 160m band. With low power, the 3KV panasonic capacitors seemed up to the task, and I saw no signs of the SWR shifting when running, so I presume they are able to handle the 100w level. With several in parallel they seemed to handle the current. Given the bandwidths I am seeing, resonance points at 1815, 1840, 1865, 1900, and 1930 should serve the purpose. Station:
The Good:
The Bad:
The Ugly:
Summary: Call: W4KAZ Total: QSOs = 200 Sections = 50 Countries = 5 Total Score = 22,825 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 and W2VJN is a very handy and well explained reference. 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 on opposite sides of a single piece 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 frequency using 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)
SCHEMATIC:
PNG image of schematic for W4KAZ’s version of the “W3LPL RX band pass filters” built as an antenna splitter and switch. Jeff, KE9V, has a blog post on an outstandingly good idea for a QSL card display. In a nutshell, scan the cards you really like, then load the images into one of the new digital photo frames. Sweet. At the bottom of this page is an accumulation of some of the SO2R resource materials I used in developing my own custom SO2R solution. My first SO2R post hashes out the thought process involved in choosing the homebrew methodology for hacking together a workable SO2R set up via home brew components. The big issues for customizing an SO2R capability appear to me to be philosophical. It is possible to wear two sets of headphones and manually switch everything, praying you don’t transmit from radio A into radio B. That is a bit TOO minimal, even for me. A minimum SO2R set up for my purpose came down to an audio switch box, a switch for the CW, microphone, and PTT, as well as band pass filters and filter switching(manual and/or automatic). And something like the Array Solutions SixPak to “keep ’em separated”[cue “The Offspring”]. It turns out none of those components are out of reach for home-brewing – if you are willing to compromise. The audio and radio input functions can coexist, but they could also easily be separated into two discrete units. One unit to handle headphone audio and the second for CW/MIC/PTT switching and route band data(if used). Likewise, the filters, switching, and band decoder for automatic antenna/filter switching can all be discrete units. The crucial decision is whether to use USB(New Hotness) versus serial/parallel(old-n-Busted) interfacing. It didn’t take very long to determine that Old-N-Busted was going to be much easier to twist up in the KazShack. YMMV, and it is a VERY subjective decision. For my own uses it is just simpler to use the parallel interface, even if it requires milking the life from a few old computers running un-supported OS’s. But I suffer no illusions that “simpler” equates to “better”. That’s a subjective call, and will depend upon the circumstances and resources available. Building a custom SO2R set-up grew out of my interest in a project by Jim, K4QPL, as well as my interest in filters, both band pass filters and coaxial stub notch filters. Being able to scout a second band will be fun, and it isn’t a great leap from a bit of extra S&P to full two radio operation. I don’t expect to be very proficient at it, but running at low power into mediocre antennas is not terribly productive either. So a full integration of the second radio into the station set-up might be fun. All of those considerations lead to researching the topic. Others have done a good job of documenting certain things via the internet, so I’m just aggregating a few of the links I found useful. Some are ideas I have incorporated, like the band pass filters. The filters merit their own separate treatment. Some of the other SO2R links discuss ideas that seem to have merit, but did not apply to my situation. Some are just good reading. The first set of links are station specific information, posted by folks describing their own SO2R set-ups. My own customized designs will be referenced first, simply because I can. But just so it is clear, my own design is an amalgamation of the work of others, including K4QPL, KK1L, and others. Many thanks to K4QPL. Jim sparked my initial interest in this project via a club program about his own SO2R project, and answered several philosophical questions that led me to my own research and experiments.
The next set of links point to reference materials or other sites aggregating similar links, or some of the commercial sources. Note: There is a lot of duplication and cross linking. K8ND’s site has a good round up of the commercial sources from here in North America.
Hardcopy Reference: 2004 ARRL Handbook, Chapter 22.47, “A Computer Controlled Radio Switch Box” Last Amended 9/20/2009, w4kaz Part 6 of the W4KAZ filter project series discusses the actual measured S-meter calibration, and the filter attenuation estimated based on S-meter measurements. As I meandered through Part 5 of this group of posts, I needed to find a way to calibrate the S-meter scale on the FT-920 to a 6DB reference. Lacking any real test equipment, this will allow me to do relative tests on the band pass filters to measure the filter attenuation on the harmonics and sub harmonic. So I used the attenuator pad(6,12, and 18db) to measure the delta between each S-unit from S-0 to S-9, “10 over S-9” and “20 over S-9”. Big shock(NOT!): The S-meter on the FT-920 is definitely not linear. Actual Big shock: The S-meter actually IS linear over part of its scale. I was a bit surprised by that. The S-meter on the FT-920 was “measured” by using the attenuator pad, inserting attenuation and noting the S-meter drop. It came out to something like this:
It was hard to decide if the drop from 20 over 9 to 10 over 9 was 12db or more, so I didn’t do any testing with any signals that strong. For the sake of an example, when the original signal was reading S4, adding 6db attenuation dropped the reading to S0. It seems noteworthy that the spread from S0 to S4 is only 6db. I can often work stations that are down around S0, and almost always work anything higher in decent conditions. I guess to me it emphasized how important just a few db difference might be to making a contact. Maybe a 1db loss throught the filters is more siginficant than it appears. To paraphrase the OM’s, “every db counts…”. Armed with that calibration scale, there now is a way to make an educated guess at the amount of attenuation a filter is providing on its harmonics and sub harmonics. By injecting a signal on the harmonic band, comparing the S-meter readings with and without the filter gives an easy way to approximate the filter’s attenuation on that band. It won’t be surprising to find that the accuracy of the measurements will be poor when compared to lab measurements, but it gives a rule of thumb guideline. Better than nothing. Amendment, 2009.06.21– Somewhere along the way I misplaced my notes with the measurements made during mid-May. It looks like I won’t have time to re-test the filters for a couple of months, so here are a few notes from an e-mail to N4YDU. The executive summary…. K4VX filters – worst case is about 30 to 35 db of attenuation, through the 20m filter. The best cases are probably 35 to 40 db attenuation on the second harmonics. NVARC Ugly filters – Woooweee! These puppies may have a bit of loss, but they sure do a great job on the harmonics. All bands showed 6 to 12 db better attenuation on the second harmonics than their K4VX counterparts. An S9 signal is dropped to S0, still readable. An S7 signal becomes barely audible at the noise floor of the F-920. The guestimate here is better than 40db attenuation on the second harmonics. Higher order harmonics were disappeared, so no ideas on the attenuation there, except that is “Enough!”. Previous in series: Part 5 Guess-timating the filter efficacy Start from the beginning at the W4KAZ Band Pass Filter series. With Field Day right around the corner the K3NG Home Brew Field Day Tarp Canopy seemed timely. I don’t have(i.e. “will not have”) a google account, so I couldn’t post comments to K3NG’s post. But it’s cool enough to bookmark permanently. Literally. Putting shade on the tent keeps the operating position much cooler. My initial reaction was that K3NG’s cover would be subject to water pooling. As I kept reading, I saw that he noticed that too. Back in the swamps as a WB5, we used a similar strategery for shade and rain. Rather than risk poking holes in the tarps with center supports, our solution was to make the front posts about 18 inches longer than the rear posts. The slope was sufficient even in a heavy rain. Our own posts were cut from pine saplings liberated from one of the club member’s farm. With the front facing north, that also helps throw the shade a bit lower on the tents below the cover. It works pretty well at shedding rain too. Lots of chances for rain on Field Day when you are only 20 miles off the Gulf of Mexico. Ick. O’course, it rained about three inches here at the NC KazShack Tuesday morning. My front yard becomes a small stream in these conditions, with water flowing over the driveway, down across the yard and over my neighbor’s driveway too. So much for the landscaping. Landscape timbers, mulch, even the grass – whoosh. I sure hope the wx dries out before FD. Ugh. Anyway, I like the rain fly solution. Kinda’ labor intensive, but worth the effort if there are enough warm bodies on hand to help throw it up. Time for a centralized list of home brew projects. So all of the following have been listed on their very own page linked in the sidebar to make it easier for me to find them. SO2R related:Other:
* Part 4 of the W4KAZ filter project series comments on the process leading up to the integrated box full of NVARC Ugly filters for use in the KazShack. The quest continues. Notes: Link to photos of the project at bottom of this page. If you want to read about the project from the beginning, go to the”Band Pass Filter Fever” series page. Part of the project goal is to put all of the NVARC filters into a switched box to allow for SO2R and use at Field Day and on IOTA expedition. The original idea was to use a simple rotary switch. Somewhere along the way the idea morphed into using relays set up to allow control from a band decoder.Toying with the relay switching idea brought up a couple of issues that I chose to avoid. Instead, the individual filters were tied together with a two pole ten position switch. A previous project resulted in a seven position remote antenna switch.That switch is lossy on 15m and 10m because of the point to point dead-bug style wiring. I didn’t see an easy way to avoid this problem, and I’m not set up for PCB design/manufacture. Using PCB’s and strip line runs would solve the issue. I have an idea for making strip lines that may work, but it is a bit Rube Goldberg-ish, so I chose to shelve that temporarily. So, back to the rotary switch. I had a 2-pole 10 position switch in the junk box. The contacts are silvered brass, and seem beefy enough for the job, so I tested it out by wiring up the input/output to a bypass position. Ick. Needless to say, it is not an ideal solution. The loss through the switch alone on 10m is about 0.6db. Losses are lower on 40m and 80m, just barely measurable. So, WTF. I used it anyway. More suitable switches are a bit pricy if bought new, and this one was already in my sweaty little hands. Impatience, “good enough”, and zero cost won out over quality. Engineer the possible. After all of that hand wringing was done, some other practical construction choices needed to be thought out. The end goal of constructing a switched filter box could have been implemented in several ways. Method 1: Use the existing set of filters, switching them in via an external switch box, all connected via a rat’s nest of coax jumpers. Method Zwei: Build another set of filters into a larger enclosure, and incorporate the switch into the new design. Method III: Use some less aesthetically pleasing choice that will also benefit from poorly conceived and hacked together engineering practices. Well the choice was clear – use Method III! The rationale unfolded as a matter of “least inconvenient compromise” rather than “optimal design”. I was limited in the number of parts available. That was the primary limiting factor for method 2, not enough capacitors of the proper values on hand for a full second set of filters. Keeping the individual filters available was desirable for the sake of future flexibility, so ripping them apart and re-assembling was not considered. Parts count also played a part in ruling out method 1, as it would use up 20-plus pl-259’s, plus the coax. My compromised solution was to use the individual filters with a slight modification. Rather than remove the so-239 connectors, I merely tacked on a pigtail of coax for the runs to and from each switch. It is a compromise in every way, electrically, mechanically, and aesthetically. But it sure was simple. It also seemed to work electrically better than I expected, as none of the loss figures vary substantially from the losses I would expect from the switch plus those of the original individual filters. In other words, the db losses through the filter added to the db losses from the switch in bypass add up to the total loss, when each band is measured separately. The completed box shows losses on all bands of approximately 1.0 db. This is a bit odd, given the losses of the switch itself vary by band. But the insertion losses of the filters are lowest on 10m, and highest on 80m. Since the losses through the switch component are high on 10m and low on 80m, they all seem to coincidentally hover in the 1.0db range. It appears that the insertion losses on 40m and 80m filters are a bit higher than the NVARC spec. This is probably because of compromises made in the physical construction, as the coils in those filters are closer to the sides of the enclosure than they should be. They were built last and the enclosure used were more difficult to work with due to their non-standard construction. The insertion losses in the 1.0 db range are significant enough to be a concern, but everything is a compromise. This is the compromise I’m required to make for SO2R without outlay of more ca$h. The ca$h reserves are currently at less than optimal levels, but there is a lot of that going on. It will be an even larger compromise operating with low power than it would be if the filters were followed by an amplifier, but such is life. Engineer the possible! In the grand scheme, the finished NVARC box shows about 0.2db more losses than I could expect from the commercial Dunestar series, and maybe 0.4db more loss than is expected from the W3NQN variety. On a positve note, this one cost less than $50.00USD in materials, not to mention everything I learned during the construction. The time required for construction was an educational investment, and was well spent. Pictures of the KazShack NVARC filter box and K4VX filter sample. Previous in series: Band Pass Filter Fever – The Guinea Pigs – Part 3 Next in series: BPFF – Guess-timating the Filter Efficacy – Part 5. |
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