|[AMRadio] RE: GB> Antenna Tuner Wonderings|
Merz Donald S
merz.ds at mellon.com
Tue Dec 14 11:14:24 EST 2004
Thanks for your reply.
OK, Yes, I understand. Some of the rigs here are homebrew and the output network designs are all over the lot. On the antenna side, there are situations here like a vertical with a poor counterpoise that will have 25 or 30 ohms to match at some frequencies. Then there's the Windom, which isn't resonant anywhere. IMHO, resonant antennas are convenient, but certainly not necessary (thank God).
73, Don Merz, N3RHT
From: Bob Macklin [mailto:macklinbob at msn.com]
Sent: Monday, December 13, 2004 5:56 PM
To: Merz Donald S; glowbugs at piobaire.mines.uidaho.edu; 'Amradio (E-mail)
Subject: Re: GB> Antenna Tuner Wonderings
With BA unit wit Pi networks you don't need a TransMatch (they ARE NOT
antenna tuners). Most will match anything between 50 and about 500 ohms. One
exception is the Heath DX-60. It is limited to 50 to 75 ohms becase of the
built in LP filter.
You need a resonant antenna for each band you want to work. Some could be
multi band antennas.
A TransMatch does not correct antenna problems. It hides them from the
transmitter. The Pi network in the BA rigs is the same thing that was in
older transmatches to connect link couples transmitters to coax lines.
It is the solid state riceboxes that really need a transmatch.
"REAL RADIOS GLOW IN THE DARK"
----- Original Message -----
From: "Merz Donald S" <merz.ds at mellon.com>
To: <glowbugs at piobaire.mines.uidaho.edu>; "'Amradio (E-mail)"
<amradio at mailman.qth.net>
Sent: Monday, December 13, 2004 2:23 PM
Subject: GB> Antenna Tuner Wonderings
> 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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