Jim
I cannot comment on the F5K and SWR, although on the F3K I was told that
there is "foldback protection" which decreases power out as SWR goes up.
This is not a method for using the radio with a high SWR, it's more of a
protection circuit when folks like me accidentally pick the wrong antenna.
I can tell you that from my understanding and education on antennas, what
you are stating is exactly correct: namely that SWR is important in terms of
loss on the coax. A commonly recommended antenna is the ladder-fed doublet
which is 450 ohm line feed from a tuner (any length, but longer is better)
with flat-top length of 130 feet. Tunes all bands and works well for a
single wire antenna.
This also relates to un-resonant verticals (the 43 footer is an example). I
put a remote tuner at the base of mine instead of using the tuner in the
rig...so that I minimize coax losses and keep the SWR in the feedline as
close as possible to 1:1 and let the remote tuner deal with the mismatch.
With only 100 watts at my station, I need every dB going into the antenna.
A more important question to answer than the SWR, is "what is the efficiency
of my antenna?" How much RF is being radiated? Resonant dipoles tend to be
very efficient, verticals generally less so.
And another question, Jim, is "what am I trying to accomplish with my
antenna?" DX? Locals? What direction DX? I have a multiband vertical
("radiates poorly in all directions" is what the old timers say), and a
multiple wire bobtail oriented towards Asia (that's where I need to increase
my country count even with easier DX like 9V1 and BY).
My 2 cents. Lots to consider. If the SWR is higher than the ATU can
handle, recommend getting a tuner for the shack which can handle it (not too
expensive, lots of good models to choose from). Or even consider a remotely
operated tuner (pricier, only works for one antenna, but very easy to use).
Mark Lunday
WD4ELG
Hillsborough, NC - FM06kb
wd4...@arrl.net
http://wd4elg.net
http://wd4elg.blogspot.com
-----Original Message-----
From: flexradio-boun...@flex-radio.biz
[mailto:flexradio-boun...@flex-radio.biz] On Behalf Of Jim Madden
Sent: Sunday, September 13, 2009 9:47 AM
To: flexradio@flex-radio.biz
Subject: [Flexradio] flex 5000a atu, swr, and astounding arrl article
I am much more comfortable in the conceptual virtual world than I am in the
physical world where what is built (by me) frequently disappoints my vision
of how things will function.
I'm currently experiencing this with my attempts to have a great antenna in
operation at my QTH, an apartment complex.
I started off with an Alpha Delta DX-CC arranged as a sloper with center
point at about 30 feet strung between trees and negotiated with apartment
management. I got reasonably good results on 20m but that was all, even
though this is a multiband antenna.
I then overlayed a mystery antenna onto this with separate coax feed lines.
This combination seems to give somewhat good performance on 20m 40m and 80m
but my intuition tells me that I am not getting the best performance I can.
Trouble is, I can't get a low SWR match using the flex 5000a ATU on 80m. I
have the minimum transmit SWR set to 3 and thus I can't transmit on 80m.
There is (to me) an astounding article on the ARRL web site called "Another
Look at Reflections" by M. Walter Maxwell, a silent key who designed antenna
systems for spacecraft. I'm still digesting his material, but if I
understand him correctly, SWR is simply not important as long as the feed
line losses are minimal which is the case for coax and ladder line operating
in the 10m to 80m range. Login to the ARRL web site and search the articles
for "reflections" and you'll find this.
He states that impedance mismatch, not SWR, is the cause of transmitter
failure. Given this statement, what protection exists in the flex 5000 to
protect the transmitter from failure? Is it irrelevant what swr I operate at
and thus I can go ahead and bump up the max SWR limit for tuning so I can
transmit on 80m? Is there failsafe protection built-in to the flex so that I
can't do something stupid and destroy the transmitter?
Would it be better to use an external tuner rather than the internal flex
5000A ATU in order to better match the transmitter impedance to the
antenna/feedline impedance? i.e. what are the limitations of the internal
ATU compared to commercially available external ATUs. Does an ATU affect
reception in a positive way or is it simply used to ensure maximum
transmitted power transfer?
Signed,
Lot's to learn
Jim
WD7W
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