To: <amps@contesting.com>
> Date: Wed, 23 Jul 97 22:40:54 +0000
> Ian and I have agreed on the screen supply since our first chat a year
> ago.
> The problem with the cathode resistor Tom is that it does not adapt very
> well at VHF and above.
OK, that would be understandable because of phase shift due to stray
C.
> I have a pair of TS940's and a nice 51J4 with all filters. Is this
> adequate? Or would I be better to use another TS940....I have 4 of them,
> all with IRCI filters? Phase noise issue?
The IMD will be well above the phase noise level. The main problem is
shielding and having an accurate attenuator.
> I also have a Ballantine 300 RMS AC Voltmeter and a HP 3400A version to
> eliminate S Meter error; simple to plug into the audio line. Ancient but
> damn accurate.
You probably need the attenuator. The dynamic range would have to be
over 40 dB with the AGC disabled. I am not sure, but I doubt the
hum and noise at the audio port would allow that dynamic range.
> I am not against spending a few Pesos to build a jig that would yield
> real results. NO...not for 10KW tubes but a few of the popular 400-1000W
> (each) tubes. I think you know Tom that my primary interests these days
> are VHF and above at serious power. Maybe in November I can get warmed up
> to 160M again.
Use some doubled sided PC board, and build a shielded housing for
the test receiver with line bypasses and a feedthrough connector to
the attenuator, and put the attenuator in the box. I used a box like
this with a screen door for access to the knobs, and a push button
precision attenuator (available from JFW and other companies, or
stolen from a scrap HP analyzer ).
> I have noticed that my 51J4 hears absolutely nothing with the antenna
> port terminated. The TS-940 is good but not like the old Collins.
Then maybe you don't need the box.
> A few guys have suggested the HP141T system but I have heard all horror
> stories about them. Any comments?
They overload easy, and so are a bit easy to misuse. If no one dumps
ten watts into the input port they usually last a long time.
> I have a nice HP8568B available at times but that is pure overkill for my
> needs. I dont mind spending a few $$ for something that will give me a
> few years of trouble free use. From what I hear, the HP141T is unreliable
> and parts are no longer available.
Old is the key word.
> What about some of these off-shore DC-1300MHz Spectrum Analyzers? Any
> experience or comments?
I borrowed a few as evaluation units and they were poor, they had
poor scale tracking and spurious responses. I'd just use a receiver,
it'll work better AND be cheaper. Just find a good attenuator pad.
A spectrurm analyzer is good for looking at broadband signals or
searching for unknown frequencies. If you know where to look, as with
IMD or harmonics, a receiver is just as good or better.
73, Tom W8JI
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