|[AMRadio] Antenna Tuner Wonderings|
Merz Donald S
merz.ds at mellon.com
Mon Dec 13 17:23:30 EST 2004
As most of you know, I am a long time BA collector and inexperienced operator. I am getting there. But it's a learning process <grin>.
I have the shack structured (in the loosest sense of the word...) into a number of stations (20-25 with about 10 in actual operation). These mostly consist of a transmitter/receiver pair with T/R relay and RX muting. The stations are in the range of 40 to 250 watts max. I run these into your choice of 5 or 6 crappy, mostly non-resonant antennas with connections being made through a home-made SO-239 "patch panel".
Most of my interest is in AM operation on or near the supposed "AM windows" on 80, 40 and 20. I have some rigs that I never change bands on. My operation is often xtal-controlled but I have VFOs on some of the rigs. Most of these old BA transmitters are pi-net outputs.
So here's the deal: I can tune any of these stations into a 52 ohm dummy load and set up the rig easily enough. Now I switch to one of my crappy antennas. And of course, it is nowhere near 52 ohms at the desired operating frequency. If the mismatch isn't too bad, I can re-tune the rig's output network. If the mismatch is ugly, or if the output network is limited in range, then I can "insert antenna tuner here" to get a match.
After a while, laziness sets in. Why should I have an antenna tuner for each rig?--especially if I never change bands on that rig? Wouldn't it make more sense to dedicate an antenna tuner to each antenna? I can use my little Palomar Tuner Tuner to match to pre-set each antenna to 52 ohms for each frequency of interest and mark each antenna tuner accordingly. Then I can simply load the rig up for 52 ohms into a dummy load, select an antenna, set the antenna tuner to my previously-marked 52 ohm point for that frequency on that antenna, patch the rig into the antenna tuner--and push-to-talk.
Ok, sure, this setup put the antenna tuner over at the patch panel and not on top of the rig. Pretty inconvenient. But hey, there's 20-25 stations to deal with here. I'm supposed to have 25 antenna tuners? OTOH, I have only 3 antennas that are sloppily non-resonant enough to require a tuner at the frequencies I am interested in. So that's 25 tuners (okay, I'm exaggerating--it would probably be only 10-15 tuners because the other stations probably have adequate output networks) versus just 3.
This trade-off seems worth it to me. But experience is in short supply here. So "pray tell me"** experienced ones, what am I missing? What is there about this idea that is bad?
Any thoughts appreciated.
73, Don Merz, N3RHT
** When Winston Churchill was named First Lord of the Admiralty in 1939, he was famous for firing off memos with questions to subordinates that began "Pray tell me...". In the Royal Navy, these soon became known, obviously, as "the Lord's prayers".
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