|[AMRadio] Re: new antenna...|
ne1s at neandertech.com
Tue Feb 6 12:30:27 EST 2007
Brett gazdzinski writes:
> Ok, the new antenna seems to work well overall,
> I seem to get good reports from the far end stations,
> and the receive signal level is very high.
> I can run full power without anything arcing or melting,
> the roller coil in the heathkit tuner gets slightly warm
> after a while on full power (600 watts carrier), which
> is likely normal, its not hot...
If it ain't broke, don't fix it! ;>)
> But I have a question.
> When fine tuning it, I found the antenna tuner would
> arc at full power until I cut the antenna down 3 feet
> on each end, and cut about 5 feet off the open wire line.
> I forget what the length was that I started with, 50 or 55
> feet each side before cutting to get the antenna tight, I
> will have to measure it next time it warms up outside.
> I assume the cutting just changed the voltage/current points
> so the tuner sees a lower voltage point.
Good assumption, I think.
> So far so good, now for the questions:
> I read that an antenna can be about 67 feet (33 feet each side)
> and fed with about 40 feet of open wire line and it will
> work on 80 and 40.
> Although it wont work on 80 as well as if it was longer,
> it will be resonant.
> The question is: Does a resonant antenna work better on
A resonant antenna SYSTEM works better on receive. You have that now if you
have tuned the system to resenonce with your tuner. For transitting on a
"short" antenna (< 1/2 waverlength overall), the more wire in the antenna,
i.e. the closer you get to 1/2 wavelength, the better. On 40M, the extra
wire certainly won't hurt you either. Were it me, I would NOT shorten the
> Since the antenna is 100 foot long roughly, will it tend to
> pick up more noise if used on a lower then resonant frequency?
I don't think so, and not in my experience.
> Does the vertical feedline acting as part of the antenna
> pick up vertical type noise?
> A 100 foot antenna would resonate someplace around
> 5 Mc? and would it pick up more noise because its resonant there?
If your system is balanced, or close to it, your feedline will neither
radiate nor act as an antenna - the signal cancels in the two sides of the
And again, your system is resonant where you've parked it with your tuner,
in order to get it to take power on transmit.
> The antenna is 100 feet long now, and the ends are right up
> against the trees, but I could add loading coils to make
> the antenna resonant at say 3880.
> Would that improve receive any?
> Would it remove the vertical noise (if any) from the open
> wire line?
The traps aren't necessary since you are using tuned feeders. You are
forcing your antenna SYSTEM to resonance. Traps are useful to force the
antenna itself to resonace, which is more important if your feedline is
> I don't know what that would do the SWR on the feedline,
> it might move the current and voltage points around, but it
> might be better overall then 100 feet.
> What do you guys think would happen if I added loading coils?
In my opinion it adds more variables and complexity with no advantage to be
Do you have a lot of noise on receive, Brett? Is there something with your
antenna's current performance you're dissatisfied with? Or are you just
trying to verify it's as good as it can be, from a theoretical perspective?
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