[Test-Equipment] HP8601A Sweep Generator

[Mike Manes]

Hi Arthur,

The HP manual specs residual FM in CW mode in low range at < 50Hz
peak deviation and < 500 Hz in 11 - 110 MHz range. The dominant 
residual modulation is characterized as "noise" rather than AC mains
frequency.  So if you're sure you're seeing 300 Hz dev with at 120 Hz,
there's trouble.

Suggest checking / bypassing the -75V supply input filter cap C9 (
50 uF) and the zener reference cap C10 (100 uF) as well.  The -75V
supply is used in generating the VCO tuning voltage.

Good luck!

73 de Mike W5VSI

Arthur Shulman wrote:
> 
> I have just taken delivery of a (like) new 8601A sweep generator that is
> apparently in perfect condition except for one minor problem: low level
> residual FM.
> 
> I am not at all sure that this is a defect or the normal operation of
> this instrument, and I wonder of anyone familiar with the peculiarities
> of the 8601A can advise.
> 
> When in the CW mode, 11mhz range at 2mhz, fm is evident on the carrier;
> I would guess, from crude measurements, that the deviation is about
> 300hz at the frequency. Of course I expect this increases (?) on the
> 110mhz range.
> 
> Frequency of this modulation is 120 hz, showing a distorted sine wave.
> 
> +20, -6.3 vdc power supply lines are free of ripple, but the -75vdc line
> shows 5 mv ripple at 120 hz.
> 
> My schematic shows this line bypassed to ground with a 10 ufd cap; an
> additional 25ufd cap from line to ground made no difference in
> modulation level.
> 
> My question is should I be concerned about this, or am I seeing normal
> operation for this instrument? I haven't used it for a 'real' alignment,
> and don't know if this is a real problem or not.
> 
> Arthur Shulman VE3ZV
> 
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-- 
Mike Manes    manes@attglobal.net     Tel: 303-979-4899
"Things should be made as simple as possible, but not more so."  A.
Einstein