[ARC5] T-19 Real World Antenna Matching Problem

[Mark K3MSB]

On Sat, Dec 29, 2012 at 6:18 PM, Christopher Bowne <aj1g at sbcglobal.net>wrote:

> Rather than using the tuner, can you resonate the antenna so it presents a
> nominal 50 ohm load at its feed point?
>

The HF2V requires a tuner on 80M.  I could build an electrically switched
network out there, but I'm surprised I'd need to do that to get the T-19 to
work at all.

>
> I match my T-19 to the antenna using a command set transmitter variable
> cap in series with the coax feed center conductor.  On the DM-33 where the
> inverted vee antenna presents a near 1:1 SWR on the wattmeter (which is of
> course in the feed line downstream of the series variable cap), I typically
> will see 40 to 50 watts output on CW, best location of the roller inductor
> seems to be at about 30-40 percent over from the left end.  At frequencies
> away from the antenna resonant frequency, I wll see slightly higher power
> indications due to reflected power adding back into the measurement.
> Generally no significant difference is tuning to a dummy load or the
> antenna.
>

This is what has me stumped.  If my analyzer is showing a proper match with
50 ohms impedance, I should see no difference when changing from the dummy
load to the antenna, or a minimal change at best.   I'm seeing a radical
change.

I am using the series 200 pF cap in series with my coax center conductor
prior to the tuner.

>
> Walt Hutchens in ER once discussed using a matching network consisting of
> a parallel resonant circuit that was tapped about three turns from the
> grounded end for the feed from the transmitter, and at about 6 turns from
> the ground end for the antenna connection.  There was also a nominal 150 to
> 200 pf cap in series with the feed from the transmitter to the coil lower
> tap point.  The  variable cap connected to the top of the coil, but nothing
> else was connected to that point.  It basically acts as an auto-transformer
> to provide better matching of the relatively high 50 ohm impedance of a
> typical coax fed antenna to the command set, the link coupling of which was
> designed to work into very low impedance short aircraft antennas with lots
> of capacitive reactance.  I built one using an old Eico 720 pi net coil and
> a command set variable and it worked quite well.  It also provides harmonic
> reduction.  Another idea I tried that worked fairly well was using a 4 to 1
> balun as an impedance matching transformer, with the antenna on the high
> side and the T19 on the low side, I think I also kept the 200 pf in series
> with the T-19 feed in that setup.
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