[HCARC] DEE-BEE's, Amps and Antennas

[Kerry Sandstrom]

I don't mind your questions at all Gary.  I just had to hassle you about not 
being on the air yet!

Yes, a dB is a dB whether it is antenna gain or amplifier gain.  With an 
antenna, the gain actually counts twice as you get it on both transmit and 
receive.  The receive dB won't help your signal but they will help you hear 
the other station.

After thinking a bit about my last e-mail, I think I did not give you the 
bottom line.   The conclusion from the station design articles of years ago, 
which is still valid, I believe,  is the cost for a dB increase in power 
output is less than the cost of a dB in antenna gain up to the legal power 
limit.  The limit has increased since those days, but I don't think the 
conclusion has.  The cost effective way to go is to run the legal limit then 
put your money in antenna improvements.  That is for DX and Contests.  If 
your interests are otherwise, then you probably don't need all that power 
and antenna.  However, an experienced operator who knows how to use his 
station is worth many dB and is priceless.  That is why on the air 
experience is essential.

A solid state Watt is just as good as a vacuum tube Watt.  There really 
isn't any difference between them these days.  I believe that vacuum tubes 
are a little more rugged and will take more abuse than solid state devices. 
On the other hand, I think the HV power supply for tubes is less reliable 
than the low voltage high current supplies for solid state.  Well designed 
amplifiers of either type will have similar efficiency and IMD performance. 
I've got a couple vacuum tube amplifiers myself and I'm not ready to trade 
them for solid state, but if I was buying a new amplifier I would be looking 
for a solid state one.

As far as PSK 31 goes, the reason they run low power is to keep their 
transmitter from generating IMD.  Odd-order IMD products are in-band to the 
signal and in the adjacent channels.  By keeping the drive down on their 
transmitters, they avoid generating a lot of IMD in the final amplifier of 
their transmitters.  As a result of running with the drive way down to avoid 
IMD, they don't have much power output and the width of their signal is 
minimized.  The in-band IMD reduces the signal to noise ratio of their PSK 
signal.  That's all that's going on there.

Have fun,

Kerry