jeremy-ca wrote:
>
> ----- Original Message ----- From: "Steve Thompson" <g8gsq@eltac.co.uk>
> To: <amps@contesting.com>
> Sent: Monday, October 01, 2007 3:08 AM
> Subject: Re: [Amps] 4CX250 IMD
>
>
>>
>>> This thread has me wondering how accurate IMD or even PEP was measured
>>> in the late 50's, early 60's. Would the readings that National provided
>>> for their 4CX1000A military amp hold up to todays techniques and
>>> instrumentation?
>>
>> My guess:
>>
>> Comparison against fixed attenuators using either spectrum
>> analyser or receiver should give fairly good accuracy of relative
>> values.
>>
>> Calibrating a diode detector against cw should give reasonably
>> accurate pep readins.
>>
>> Steve
>
>
>
> Thats exactly what I was getting at.
>
> Fairly good, reasonably accurate, dont exactly give me a warm feeling.
> Having worked in a RF lab with 50's era test equipment in the early 60's
> I always had the feeling that accuracy wasnt that great in our SA,
> calibration and readings. EVERYTHING drifted back then which some here
> dont realize. We were barely out of the dark ages. The SA alone was a
> rack mounted monster with a "zillion" tubes that seemed to be getting
> repaired as much as it was used.
I know the sort of stuff you mean - and the variations and drift. Better
accuracy takes time more than anything because you're probably not using
a swept analyser, and having to make numerous comparisons. I'd expect to
be able to get to about a dB on relative IMD levels and 5% on pep ref a
cw measurement. I can imagine someone making that much effort for a data
sheet, maybe not for production test.
Steve
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