[Lowfer] Where is everyone tonight???

[WE0H]

I'll use the meter for 136kc, as my transmitter will be sitting on my desk
next to the HP. My FET amp design is simple and very small. It will use a
fan on the heatsink to keep things cool enough. I will use the push/pull
final that most of us use now for a driver before the FET amp. There is a
tiny IC stage that takes the HP's signal and squares it up as well as
bringing it to TTL levels for the driver stage. All of this is not much
bigger than your open hand. My lowpass filters are designed to transform the
finals output impedance to 50-ohms and the Tuner Box's transformer is built
for a 50 to whatever impedance transformation. This is just the way I chose
to do it here, everyone has their way of matching and that is fine.

Mike>WE0H
http://www.we0h.us/lf.html
185.303kc QRSS-30/CW@15wpm
ID is "WE"

-----Original Message-----
From: lowfer-admin@mailman.qth.net [mailto:lowfer-admin@mailman.qth.net]On
Behalf Of Bill Ashlock
Sent: Sunday, July 28, 2002 12:34 AM
To: lowfer@mailman.qth.net
Subject: Re: [Lowfer] Where is everyone tonight???

Mike,

Of what use is an SWR meter? If your final is at the base of the loop, where
it should be, (even at 136k) there is no such thing as an SWR. The input AC
resistance of the loop (.4 to 2 ohms) is where the power is dissipated and
the transformer turns ratio can be anything depending on the power you want
to run. The output impedance of these transmitters is very low, like 1 ohm.
Lyle is wong on this if he says "50 ohms", unless this is the effect of the
filter. In my case I have to insert a 60 ohm resistor in series with the
exciter output and the 70ft, 70 ohm coax to the final box. If I don't do
this the exciter transistor pair run hot and it's because of the poor match
to the coax. And I've never had much luck with that output filter of his.
Very hard to vary the frequency when using one without changing the output
waveform considerably.


My concept of a 100w final is a stage not that different from my little
final out in the woods. Maybe a little heat sinking will be needed similar
to that used on a 100w switching supply. These European 136ers that suggest
large transmitters for 100w are too used to traditional Ham transmitters.

Bill