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.64λ Homebrew
- Thread starter HomerBB
- Start date
I may have already mentioned this, but I find that these good and bad points seem to peak at physical 1/2 wave intervals according to the models.
So, if 50' feet looks good, and if that is hard to reach, then try 32' feet for a good response and maybe 36' for a poor response.
Looks like you might already be close to a good height at 34.5' feet according to my 5/8 model. Maybe if you can, try and raise it a 1.5' foot and see if it gets worse at 36' feet as my thinking here would predict, but don't stress over it.
BTW, if you have a mobile FSM with a small antenna, try sitting the meter on top of the radio or your meter. You may also be able to attach a shorted section of small coax, like I do with my digital meter, and that antenna should provide a lot more sensitivity.
If you check below your antenna, then try an set the meter's antenna very close to the mast and set the sensitivity to max to start. You may have to make adjustments however if the currents are strong. Polarity seems to have a strong effect on my FSM results as well.
So, if 50' feet looks good, and if that is hard to reach, then try 32' feet for a good response and maybe 36' for a poor response.
Looks like you might already be close to a good height at 34.5' feet according to my 5/8 model. Maybe if you can, try and raise it a 1.5' foot and see if it gets worse at 36' feet as my thinking here would predict, but don't stress over it.
BTW, if you have a mobile FSM with a small antenna, try sitting the meter on top of the radio or your meter. You may also be able to attach a shorted section of small coax, like I do with my digital meter, and that antenna should provide a lot more sensitivity.
If you check below your antenna, then try an set the meter's antenna very close to the mast and set the sensitivity to max to start. You may have to make adjustments however if the currents are strong. Polarity seems to have a strong effect on my FSM results as well.
Have you had much of a chance to test the performance around town compared to your other antennas?
Hey Marconi, How high was your Gainmaster mounted above the ground?
How does it look in the models if it's right at 36"?
Well if the choke is working like it should, then such a test could be dubious, since we're looking for a bad spot to tell us something.
I didn't think about that, but I've had numerous chokes that I thought would work or had previously worked, and in the next install, they failed to work. You will have to figure that out based on the trouble involved, and if your choke is removable, or if it is a part of the physical feed line coax.
BTW, regarding chokes, several times I got frustrated when I did a bandwidth curve on an antenna without a choke, and when I added a choke using barrel connectors, the bandwidth and the match changed on me.
I think it is best to make the choke using part of the same feed line, so that you don't effectively add feed line length, and for sure if you plan to chart your match under these conditions. This caused me to chase my tail a bit, while trying to figure out what was going on. I questioned, that I had really stop the CMC, so that the feed line now showed a better match by stopping the current, or was something else going on, like feed line transformation? You'll never know for sure if you change two things in your system under a single test.
Maybe another worthwhile discussion.
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Everyone is out of doors right now, so not much local radio going on. I will report on it as soon as I can.
Marconi I'll try the FS meter things you suggested.
Marconi I'll try the FS meter things you suggested.
Do you have a decent low pass filter lying around? If you run the amp; then having a filter inline when testing the antenna might bring the TVI way down. Might not be the antenna's fault at all. Might be the amp throwing off spurious emissions instead . . .
NB, my model for a GM is a 22.5' wire radiator that is center fed, and thus no combination of model height will produce the appearance of no CMC on the feed line or mast, unless I isolate the mounting end.
I'm not good enough to model the GM with a true duplication of the actual antenna, so I can't be sure that this modeling idea will produce results that would be of value to a follow-up question...that I suspect you have.
My 22.5' foot GM is set at 38.5', because that is as high as I could get it at the time. From the looks of my pole, it could go up an additional 8'-9' feet, as I added a 10' section to my 40' footer. As it turns out, I could have saved myself all of the trouble.
With my original Starduster mounted at 46.5' to the hub and mounted beside the GM, they both work very well, and about the same. As best I can tell they both work local and DX the same, and that amazes me based on what I hear and the fact that the SD'r is 6' feet below the tip of the GM.
How have you been. Haven't heard from you lately.
When I replaced my 42' high Imax with the Gainmaster I went from s8.2 to 3db over s9 to a station 9 miles away using a Penetrator and an Amateur radio with analog meter.
When my friend Jack replaced his 36' high Imax with a Gainmaster he saw no real difference.
I'm beginning to wonder if RIGHT ABOUT AT 1 WAVE LENGTH is a bad height for the Gainmaster, for whatever reason.
When my friend Jack replaced his 36' high Imax with a Gainmaster he saw no real difference.
I'm beginning to wonder if RIGHT ABOUT AT 1 WAVE LENGTH is a bad height for the Gainmaster, for whatever reason.
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When I replaced my 42' high Imax with the Gainmaster I went from s8.2 to 3db over s9 to a station 9 miles away using a Penetrator and an Amateur radio with analog meter.
When my friend Jack replaced his 36' high Imax with a Gainmaster he saw no real difference.
I'm beginning to wonder if about 1 wave length is a bad height for the Gainmaster, for whatever reason.
How can it be a bad idea? Any 5/8 wave antenna @ 1 wave length high is going to reap the benefits the lowest possible angle of radiation and the ability to get it to skip farther.
I would think this holds the answer...
see where the pattern is not completely round.
there is a 3 db difference where the pattern is not at max radiation.
Here is link in case jpeg is blurry..http://www.gain-master.it/vsconventional.php
see where the pattern is not completely round.
there is a 3 db difference where the pattern is not at max radiation.
Here is link in case jpeg is blurry..http://www.gain-master.it/vsconventional.php
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When I replaced my 42' high Imax with the Gainmaster I went from s8.2 to 3db over s9 to a station 9 miles away using a Penetrator and an Amateur radio with analog meter.
When my friend Jack replaced his 36' high Imax with a Gainmaster he saw no real difference.
I'm beginning to wonder if about 1 wave length is a bad height for the Gainmaster, for whatever reason.
NB, you reported what you saw no doubt, but in my experience I sometimes see a glaring difference too, so I test as many contacts from the same stations as I can and I try to select stations at different directions and distances. With luck and any reasonable consideration...that should tend to smooth out results and mitigate the occasional aberrant signal that comes our way from some contacts. One test does not seem reasonable enough to make such a judgment IMO.
Do your other local contacts show as much difference in signal with those two antennas?
Gamegetter, I may be missing your point, but below is a 5/8 wave model produced by Cebik in an article he wrote. This is a Free Space model to be accurate, and that has to be considered if you are thinking about antennas working over Real Earth.
The Sirio model above is also shown in Free Space, and that means there are no losses involved, and the Earth's influence on the pattern is excluded. You will note that the antenna models are very similar if not identical.
View attachment Gamegetter's idea.pdf