Radio W4KAZ Thanks for stopping by the virtual KazShack. Feel free to comment - I often approve them.
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By w4kaz, created on 2009.07.17 at 05:28:26 | last changed on 2009.07.23 at 19:30:56 | IARU is a contest that gets better participation outside of the US. Its early summer time frame gives it a different twist for radio propagation, and it is only a 24 hour contest. The time frame means that you may only get one chance to work certain regions, so if you snooze you lose. But unlike a DX contest based on country borders and continents, it also allows for the US stations to work each other. Another thing that makes it enjoyable is the dual mode nature. It is a little bit of everything. Unique.
This is normally a favorite contest to work from the shack, although I seldom press it as hard as I might in others. I was not really looking forward to it this year because of continuing poor propagation, but I brightened up when N1LN and N1YXU decided to host a Multi-Single at their QTH. (and many thanks to N1YXU and N1LN for hosting the event!)
I needed to split my time for last Saturday anyway, so I asked Bruce to put me on the graveyard shift, which he did. He had rounded up quite a few people for staffing the active station. As it turns out, the crew was a good mix of CW and SSB talent. AA4XX and EA5DFV both joined in to the fun. Paul, AA4XX is a local ham who enjoys QRP operation. Our friend Jose’, EA5DFV is contest op for Spain who is vacationing in the area visiting his family. It was really good to get to know both gents better.
Jose’ also pulled the graveyard shift. He and I were up for the duration of the evening. W0UCE covered the first part of the evening for CW, and N1LN got up in the early morning to finish up the contest with us.
My own head was mostly “in a box” for the evening, so I had a great deal of difficulty concentrating. That made for less running and more S&P. Conditions were very noisy, which is a situation I usually struggle with when I am alert. I’m afraid my performance probably was an overall drag on the team.
On the positive side, I gained the benefit of being mentored by an experienced EA op. Jose’s insight into the thought processes he would be using if he had been at his home QTH were very enlightening. We began searching for multipliers as morning approached. This probably was a good choice for the score, as the run rates we were getting were low enough tha even a single mult was worth the 10 to 15 minutes on the other band.
The early am hours(0700z) were fun for me because of the openings to the Pacific area. This is somethig I don’t get much of with the LP/wires set up at home. At N1LN’s I began hearing VK’s on the middle 20m antenna. Later in the morning(1000z) the JA’s were coming in on the top antenna. But there was also some sort opening to the VK’s on the compass heading for the JA’s at that time. When I switched to the lower antenna pointed directly at them NOTHING was heard.
As always, the social aspect of the evening was just fantastic. Bruce and Laurie are wonderful folks. I made sure to put in a reservation for Chef Archie’s(W0UCE) dinner. We made wise cracks at UCE’s expense all evening, but the meal he prepared for the group was one of the best I have had in ages. Chef Archie gets four stars from el Escribano Inexacto.
The N1LN 3830 write-up.
By w4kaz, created on 2009.07.04 at 05:12:58 | last changed on 2009.07.06 at 10:01:21 | 2009 FD was an expedition out to the Western NC Appalachians. N4YDU, N4PY, K4CZ and myself operated under N4PY’s call in Stone Mountain State Park. NC, not GA. Not at all the same as Stone Mountain in Georgia, as our own ancient granite lava dome does not sport the bas relief artwork.
The WX here turned out very well. Saturday was on the warm side, but Sunday was cooler, and rain was not a problem. Not a cloud in the sky. Happened to also spend Monday and Tuesday in Boone, and the WX was the sort the chamber of commerce there uses for advertising – it was that pretty.
The shelter reserved for the FD purpose was perfect for a 2A setup, which was fortunate for our planned 2A operation. We were able to mount all of the planned antennas, and were able to find a suitable spot on a down hill slope for the generator.
This year’s score was down from last year’s 3A effort, and we had only four operators this year. We wound up with about five hours of downtime of the 48 hours of time available(24 hours on each station). That allowed us to log 1946 QSO’s(including dupes), which came out to be 6564 Qso points. With bonus points we should have a final score of around 7200. Not too shabby for just four guys.
Everything seemed to go smoothly from set up through tear down. We had about 500 CW QSO’s on both 40m and 20m, but for my own part, the 40m Q’s were much more difficult due to high noise on the 40m antennas.
The Good:
The Stone Mountain site was perfect. Set up went smoothly. WX Conditions were good. Radio conditions were fair to good, which means much better than 2007 and 2008. No bear vistits, slithery reptiles with noisy tails, or two-legged snakes. Very few biting bugs.
The Bad:
Long drive to the site(except for N4PY). Campground was nearly full early Friday. Bugs really seem to prefer CFL lighting – perhaps its a correlation to their communist hive mentality at work. Big scary spiders…Augh! Lost track of the baluns, needed one of them on site.
The Ugly:
High noise levels on 40m. This was unusual, as the 80m noise was not as high. The noise on the E/W antenna was S7+ and was S5 on the N/S antenna. The N/S antenna was plagued by RF feedback (I somehow misplaced the baluns during packing/repacking). If I were to do it again I think I’d give the 25KV utility hub a good scan with an AM radio to verify it as the source of the QRN, then see how the antenna placement might be improved. Perhaps the high band antennas could be placed nearer to the utility box(i.e. where the 40m antennas were). 20m up might be more resistant to the RFI.
Packing Notes:
- Missing the baluns.
- Didn’t need the filters.
- No more CFL light bulbs for FD – bug magnets!!!!
- Need extra lightweight cords for the FD lighting
By w4kaz, created on 2009.06.22 at 06:11:05 | last changed on 2009.07.06 at 11:19:47 | 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:
- S0-S4 – 6db
- S4-S5 -6db
- S5-S6 – 6db
- S6-S7 – 6db
- S7-S8 – 6db
- S8-S9 – ~9db
- S9-10 over 9 – ~12db
- 10 over to 20 over – **Not measured**.
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.
By w4kaz, created on 2009.06.19 at 06:58:14 | last changed on 2009.06.20 at 08:30:59 | 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.
By w4kaz, created on 2009.06.17 at 05:49:08 | last changed on 2009.06.14 at 22:29:53 | The FD results for the 2008 FD were put online back in February. But as we bear down on FD 2009, time to review. The N4PY crew managed to win the Roanoake Division in class 3A. We finished in 10th place overall of class 3A., and 63rd for all entries regardless of class.
Not too shabby for seven guys in a completely new and untried location.
We were beat out locally by the OCRA crew, who put up a really good score operating in the 5 watt battery class. Also K4QPL squeaked by us with about 50 more QSO’s in class 2A, although we had more points.
But on a “QSO per Peep” basis we did rather well. There are only a handful of other stations that managed to lay out as many QSO’s per person with as few people as we did. Most of those were two man set-ups. Sweet.
Maybe if we find a BBQ staff N4YDU will be able to add another 1000 Q’s to the total.
- 1st of 8 and of 21 ,class 3A, in the NC section andRoanoke division
- 4th of 73 overall in the NC section
- 11th of 188 overallin the Roanoke Division
- 10th of 303 in class 3A nationwide
cqfd cqfd cqfd…..
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 2009.06.05 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
------------
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.
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