On 1/24/2014 8:00 PM, Ralph Mowery wrote:

"Jeff Liebermann" wrote in message
...
On Fri, 24 Jan 2014 13:04:48 -0500, Jerry Stuckle
wrote:

The easiest way of seeing it is looking at the output of both tube and
transistorized transmitters on a spectrum analyzer. You will see much
more hash on the transistorized transmitter.

Amazing. You might see more hash with a synthesized transistor
xmitter, but for crystal controlled, they noise is quite a bit less
with transistors.

Back in the 70's, I ran a CAP repeater from my home. Transmit and
receive antennas were separated by about 25' vertically. It was a
surplus Motorola tube rig, running 25W. I was able to run it without
any desense without duplexers. Yes, the channel spacing was 4.25Mhz,
but you can't do that with a transistorized rig.

Amazing. These days, 2 meter repeaters do 0.600 MHz spacing using all
transistor equipment, a single antenna, and a notch type duplexer.



What you are saying is more in my line of thinking and limiated expierance.
Around 30 years ago I had an Ameco 2 meter receive converter that used the
6ds4 nuvistors. Probably the best tube that most could afford. Tuned for
the best signal, I could still improve it when adding a u310 preamp. Not
sure how much as I did not have very good test equipment, but noticiable by
ear. I think many of the old sets used a 6ak5 for the rf amp.

Transmitting noise I don't know. All I was looking at was the noise figure
for the receiver as that was the origional topic.

What Jerry was talking about was a tube CAP repeater with seperate antennas.
If the receiver was around .5 uv or worse and the transmitter was cleaner he
could operate with seperate antennas . He said he could do that with the
tubes but not the transistors which I believe. Beter selectivity on the
transmitter and receiver than some transistor repeaters.

I do have a 2 meter repeater on the air with 600 khz seperation. Solid
state and 100 watts. Right now it has a Dow East Microwave phet preamp on
it. Don't recall the exect sensitivy for 12 db sinad but it is under .2 uv
as shown on my hp8924c.
No desense is detected. It does have a 6 cavity bpbr duplexer with the high
selectivity option.


Receiver sensitivity was 0.2 mv for 20db S+N/N ratio. I don't know
how much better; the surplus signal generator I was using wasn't that
accurate.

And BTW - 'm' can also mean micro, especially when you don't have a
Greek alphabet available. 'u' is not the same as the Greek 'mu' and can
be confusing. Of course, using 'm' for both milli and micro can be
confusing, unless you know the context.

--
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Jerry Stuckle

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