Towertalk
[Top] [All Lists]

Re: [TowerTalk] G5RV vs 40M dipole

To: towertalk@contesting.com
Subject: Re: [TowerTalk] G5RV vs 40M dipole
From: David Gilbert <xdavid@cis-broadband.com>
Date: Mon, 27 Apr 2015 11:30:03 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>

Certainly the SWR on the line adds loss to the system, which is why it can be desirable to do the matching at the antenna to avoid it. But doing it at the rig is typically much more flexible, is typically less expensive or complicated, and depending on the situation might be just as effective in practical terms. As WA4LAV says, that transmission line loss is not always hugely significant since it depends upon the matched loss in the line itself (which varies with frequency and the quality of the line), the length of the line, and the magnitude of the SWR. Using a transmission line program like TLW (available free with the ARRL Antenna Book) will pretty much tell you exactly what you have instead of you having a false sense of anything.

73,
Dave   AB7E

On 4/27/2015 9:36 AM, Tom Osborne wrote:
One thing I have noticed with the built-in tuner on my radio is that all it does is make the radio happy.

The radio shows a 1:1 SWR, but the meter past the radio still shows a high SWR, so if there is loss on the line, even though the radio is happy, the loss is still there. I think the tuners just give us a false sense of security. 73
Tom W7WHY

On 4/26/2015 9:23 PM, Fuqua, Bill L wrote:
Not everyone knows that a tuner only protects the rig. That is the job of a dummy load. In fact the tuner matches the impedance of the antenna system to the rig and not only that, by doing so providing the antenna with a conjugate match, that is to say the antenna's radiation resistance is matched and its reactance is also matched by the equal and opposite reactance thus making the antenna system resonant. If the antenna has a radiation resistance of 10 Ohms and a capacitive reactance of 100 Ohms the antenna tuner matches it with 10 Ohms real resistance and an inductive reactance of 100 Ohms thus providing maximum energy transfer. While at
the same time it provides 50 Ohms resistive load for the transmitter.
Resonating the antenna system with a tuner is equivalent resonating the antenna. The only difference is that there may be some additional losses within the tuner and transmission line which are generally minimal at HF frequencies. Also, there is a reduction in bandwidth of the antenna system. Yes it does change the currents and voltages in the antenna. The G5RV was an antenna developed back when we had tube transmitters with a PI network output that could accommodate a broad range of
impedances. It also was made to work on 5 bands.
Just about every AM broadcast antenna system has an antenna matching network. It is a shame that
they don't work.
73
Bill wa4lav

_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk


_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk

<Prev in Thread] Current Thread [Next in Thread>