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By w4kaz, created on 2009.06.11 at 05:09:57 | last changed on 2009.07.06 at 10:05:40 | 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 Losses:
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.
The Guess-Estimate:
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 50Ö¶ 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.
Previous in series: Band Pass Filter Fever – The Kludgy Switch Box – Part 4
Next in Series: BPFF – The Guess-timated Scale and actual Guess-timates – Part 6
By w4kaz, created on 2009.06.08 at 05:33:00 | last changed on 2009.06.08 at 11:21:50 |
By w4kaz, created on 2009.06.05 at 06:58:08 | last changed on 2009.06.05 at 06:59:16 | WPX from the cheap seats……
I was a little disappointed at first, since I missed most of the better band conditions. Mostly operated during the early evening and both afternoons. After a good night’s rest and most of a week later, it turns out the contest looks better than the first impression.
This contest was mostly a shakedown cruise for a lot of shack and antenna system changes revolving around setting the place up for SO2R. The shakedown was a success.
All of the home brew items seemed to function well. One minor glitch in the SO2R box. It would appear that I managed to wire the left and right channels reversed. Good thing the headphones I prefer are “ambidextrous” – that work around was easier than sitting backwards. 😮
Two sets of home brewed band pass filters worked well with low power, even though the KazShack antennas are practically touching one another. The set of K4VX filters were augmented with coaxial stubs. The worst case interference is between 40m and 20m, where the harmonic is about S6. 80m/40m are completely free of any interference, and 40m/15m are also friendly.
The big lesson learned was that SO2R will be a lot of fun, once I become proficient at SO1R. It became obvious that I am NOT yet a proficient operator, not that I had any doubts there. It was great to be able to S&P while running at low power, but I did flub some Q’s on the run radio by being distracted.
Having the audio from two radios, one left ear, the other right ear, was not as large a problem as I expected. I wired the audio controls for the SO2R box into a small remote box that snuggles up next to the keyboard. On it I wired a momentary contact switch for each band. The buttons make it easy to put either left or right radio temporarily into both channels on the headset for digging the weak ones. I had the switches, didn’t have a pot for a mix control.
For the most part, having audio from the left radio in the left ear and the right radio in the right ear was less difficult than I expected. It seemed very similar to listening to a big DX pileup. The only time it was confusing was when the left and right stations were zero beat, and CQ’ing simultaneously at the same speed. Hearing the zero beat CQ’s then suddenly go off into different call signs was disconcerting.
I really enjoy S&P operating. The SO2R set up really does make S&P twice as much fun. I don’t normally use spots, but I’m curious to see what sort of rate I can manage banging spots with two radios. Probably try that in 2009 Sweepstakes.
Things to fix: Fix the SO2R audio switching. Additional stubs for 40m and 20m. More SO2R practice.
Things to try: When running at a decent rate, try using the second radio to load the band map with spots. Then if I lose the run frequency, sweep through the second radio spots while hunting for another run frequency. Until I’m a better operator, it is too easy to lose the run frequency trying to work a station on the second radio.
The Good: No problems with any of the KazShack or antenna changes. Bandpass filters worked. The SO2R box handled switching radio control properly. The dipoles at 90 degree offsets worked for bringing stations up and for nulling interference. The new 20m antenna could hear an AK station at about three S-units higher then the original antenna, which could scarcely copy him. More total QSO’s than expected. Actually held a run on 40m from the run poachers. I made about 50 second radio QSO’s while running on the other radio.
The Bad: Not much productivity to Europe. Missed the 10m and 15m openings. Most of my operating time was in the off-peak times.
The Ugly: Got sick as a dog and bailed on Saturday evening. Being sick was probably why I was so tired Friday night too.
Summary:
Band QSOs
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160:
80: 3
40: 241
20: 218
15: 38
10:
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Total: 500 Prefixes = 304 Total Score = 376,048
Next up ......Field Day!
By w4kaz, created on 2009.06.01 at 06:59:33 | last changed on 2009.07.06 at 10:10:07 | 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.
By w4kaz, created on 2009.05.27 at 05:08:11 | last changed on 2009.05.27 at 06:23:47 | Finished wiring up the control cables for the Array Solutions SixPak. There’s a mistake on one of the control cable assemblies that were too hastily assembled, a W4KAZ problem, not anything wrong with the SixPak. The work around was easier than re-wiring the cable, so I just re-connected the wires inside the control box to fix the problem.
Using Cat5 cable, the color coding inside the KazShack “Should Be” as follows:
- 10m – orange
- 15m – white/orange stripe
- 20m – green
- 40m – white/green stripe
- 80m – blue
- 160m-white/blue stripe
- 12v or gnd – brown and white with brown stripe
- (tied to #7)
Note: The SixPak wiring block in the controlboxallows 12v+ to be sent down one cable and 12v gnd on the other cable. I could just have easily sent 12v+ down wire #7 and used wire # 8 for ground. That would allow the SixPak to function using either switch position alone with a single control cable. That’s also probably how most folks would wire the cables, since at leastone radiowill work when wired that way.
For quick connects, I used a set of 8-wire computer power cable extensions(ATX power extensions). Each extension is 8 inches long, and cutting one in half gives a mating connector pair. Easy enough to splice on, but I obviously screwed one up somewhere. When testing, Radio B was found to have 10m/40m and 15m/20m pairs reversed. Again, rather than re work the cable, I just rewired the four appropriate wires inside the control box, and taped a sticky note inside the cover to remind me I dorked up that radio B cable assembly.
Now a bit more cable assembly will have most of the bits in place for some new operating fun.
Outstanding KazShack Issues:
- hoisting 15m loop
- 10m antenna(???what to try???)(???and why bother???)
- 160m antenna on ground
- 40m antenna switch
- 20m antenna switch
- Tuning K2 for 80m/160m
- Shack layout redesign
- Operate!
By w4kaz, created on 2009.05.24 at 06:05:58 | last changed on 2010.09.28 at 17:14:15 | Whilst toying with some new KazShack toys, I found out an interesting and useful fun fact. The 80m folded dipole does a great job at ignoring some of the AM harmonic mixes. Death to harmonics! W4SAT seems to have the best on-line description of a folded dipole.There is very little written on the internet about this great antenna option. My own original post has a link to a web reprint of the original ARRL design article.
The KazShack is less than a mile from the 50KW WPTF(680) transmitter, and only about two miles from the 10KW WRBZ(850) transmitter. This results in all manner of harmonics and harmonic mixes that I can hear and identify. Pretty much any combination of the numbers 680 and 850 added and subtracted together produce a frequency that have audible audio artifacts that can be identified as from either AM station. Some of the mixes are much worse than others. Some are barely audible. The mixes that fall within the ham bands are obviously the ones of the most pertinent concern.
While playing with some new home brew band pass filters filters and the SixPak, I flipped the radio to 80m. While connected to either 40m antenna or the 20m antenna, I could hear a loud garbled mix centered at about 3570. The WPTF audio was clear. The WBRZ audio was also identifiable, although very garbled. That works out to the 4th harmonic of WPTF mixed with WBRZ’s 850. (i.e., [4*680]+850=3570)
This seemed really curious, since this never seemed to be a problem before. On the 40m antenna broadside to WPTF, the mix was S9+, and at least S7 on the other 40m and 20m antennas. So, it will probably blow my socks off when I switch to the 80m folded dipole, right?
Nope. Switching to the 80m folded dipole, the mix disappeared completely. No more WPTF audio on 3570. No more WBRZ. Both were Gone. Zip, zero, nada. Hmmmm.
Then I rememberated reading that folded dipoles were useful on their primary frequencies and their odd harmonics. So an 80m folded dipole could possibly be pressed into service on 30m, but it is deaf as a dummy load on 40m. That was a fact I have proven experimentally, both on purpose and by accidently flipping to 40m and wondering where all of the signals have gone(duh-uh!). The 80m antenna was rejecting the WPTF fourth harmonic well enough to eliminate the two station mix.
It would appear that a folded dipole also helps to reject the even sub-harmonics as well. This would probably have been obvious, but the thought had never crystalized within my addled gray matter before that moment. That fact could prove very useful for several settings. SO2R. Field Day. Field DXpeditions. IOTA. Sweet.
So, one additional yet seldom documented method to reduce the n/2 sub harmonic is to use a folded dipole. I would expect the folded dipole will also attenuate an interference your transmitter is generating on it’s 2nd harmonic, so switching either antenna to a folded dipole will probably help. This won’t help a 40m/15m problem, but applies to the other common harmonic situations.
Every little bit helps.
By w4kaz, created on 2009.05.18 at 05:16:06 | last changed on 2010.10.01 at 09:05:34 | So, a long hiatus between band pass filter musings. In Part 1, I laid out several reference sources for band pass filter projects. Part 2 details the decision process, plus some notes on what happened with initial attempts at reproducing the K4VX Filter and NVARC filter projects.
Here I have a bit more detail on each project. After obtaining a small supply of the capacitors specified by the NVARC design, I’ve completed the 40m and 80m filters.
Measurements on the 40m NVARC filter show about 0.8db loss through the filter, with the SWR pass band covering the entire band easily. Outside the band, the SWR rises rapidly above 7.370 Mc, and below about 6.775Mc. That would seem to indicate the filter is resonant lower in the band, but it actually shows about 2 watts more attenuation at the bottom of the CW segment than it does at top of the SSB area.
The 80m NVARC filter also shows about 0.8db of loss through the filter. The SWR is about 1.5:1 across the entire band, and the filter seens to have its sweet spot right near the SSB DX window at about 3.775 Mc. That should prove fortuitous, since it is also where my 80m folded dipole resonates, but it is completely by chance.
These last two filters probably have slightly higher losses than they should due to construction techniques. The cases I had available for their enclosures were not ideal. Their assembly did not allow easy construction by the NVARC guidelines, and the coils are probably mounted less than optimally inside their cases. Through experimentation I found that slight variations in coil positioning had an effect on their insertion losses.
Additionally, the 15m filter began acting up, showing terrible losses. It turns out that in slinging it around the shield had become dislodged and was either in contact with or too close to one of the coils. Re-securing the shield solved the problem, and put the filter back very close to the NVARC spec’d performance.
By comparison, the K4VX set I have show less attenuation. I have K4VX versions for 20m, 40m, and 80m. Both the 40m and 80m filters show very low losses through the filters, both at about 0.3db of loss, only a couple of watts. The 20m version shows losses similar toits NVARC counterpart, in the vicinity of 0.7db. I expect to rebuild the 20m filter from this series using the ceramic caps rather than silver mica caps. It will be interesting to see if the loss figures change.
I have not yet built the 10m and 15m versions of this design, and may not. The attenuation specified by K4VX on these bandsis not as good as the NVARC spec. It might be worth trying the NVARC filter designwith toroids rather than air wound coils. An excellent experiment idea, and the 10m and 15m NVARC design seems to work well as described and reproduced here.
Given the low losses through the K4VX design, I may use that set for the run station, and the NVARC design for the mult station in an SO2R setting. The K4VX design is also physically much smaller, another practical advantage. The NVARC design has a better set of attenuation figures specified, but it will be nice to get actual measurements on the filters before declaring them a better choice. Some actual on-air testing can’t hurt either.
The coax stub project has been placed on the shelf for the moment. It is worth noting that coaxial stubs are probably better described as notch filters rather than band pass filters, as they are designed to place a notch on the harmonic or sub-harmonic frequencies. The book by W2VJN, “Managing Interstation Interference – Coaxial Stubs and Filters”is a treasure trove of useful information. For anyone with an interest in the subject of coaxial stubs, the book is worth every red penny of its price. Add it to your library and you won’t be displeased.
Previous in series: Band Pass Filter Fever – Untangling The Web – Part 2
Next in Series:Band Pass Filter Fever – The Kludgy Switch Box – Part 4.
By w4kaz, created on 2009.05.15 at 05:07:29 | last changed on 2009.05.13 at 20:07:43 | Don’t miss the best source for up to date contesting news available on the internet. The new source for all manner of contest trivial is now up and running at the home page of the Lost Island DX Society. I sure wish I were going to be at Hamvention this year to catch the L.I.D.S. hospitality suite.
By w4kaz, created on 2009.05.12 at 06:43:37 | last changed on 2009.05.12 at 06:43:37 | PVRC club members received word from PVRC president Ken, K4ZW, that PVRC will be introducing a series of Webinars on various contest subjects. Jamie, NS3T has a news release posted with a bit more info. Most of the webinars will be available to all contesters, although I suspect there may be a few club internal “stategery” sessions held more tightly to the vest.
I sprung for the original PVRC 2005 “Contest College” DVD, which has a lot of great information on it. Not every subject was a priority interest to me personally(e.g., VHF contesting), but each was well conceived and delivered. Really wanted to make the original PVRC “Contest College” in VA, but could not.
PVRC Contest College evolved quickly beyond the club into Contest University at Dayton Hamvention, and has already been taken internationally by K3LR, drawing on local talent for lecture sessions. Given the hundreds of years experience held in the minds of so many great operators and technical folks, this is a great idea.
A repository of simlar webinars would be a great asset. It will be of greatest benefit to folks who are in rural areas, and not able to get the sort of elmering that can be obtained by joining a club, or who cannot make a long pilgrimage to CTU at Hamvention.
Built it, and they will come….
By w4kaz, created on 2009.05.08 at 06:22:23 | last changed on 2009.05.06 at 20:25:07 | Or a way to kill time. WB4AEJ has a matrix with a slew of assorted hame domain links. Just scratched the surface….
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