[R-390] HP-8640B vs. HP-8654A/8655A/11710B

[Cecil Acuff]

Make sure the 8640B has a fully operating gear train.  The plastic gears are 
a weak spot in these generators.  I'm not aware of spares either.  One that 
works is a nice machine...

I have one and a 606A...

Cecil...
----- Original Message ----- 
From: "Barry" <n4buq at knology.net>
To: <R-390 at mailman.qth.net>
Sent: Sunday, January 09, 2011 9:21 PM
Subject: Re: [R-390] HP-8640B vs. HP-8654A/8655A/11710B


>> Well, the 8654 (A or B) was never intended to be an 8640B-class
>> generator.  In terms of signal purity, it may be the dirtiest RF
>> generator HP ever made, including the earliest synthesized
>> models.  Fine for basic alignment, but not really useful for
>> twin-tone IM measurements or anything fancier.
>>
>> These days, one would typically use it with a counter -- but be
>> careful, the auxiliary output on the rear panel is not well isolated,
>> and any crap that comes out the counter's input (not at all unusual)
>> can end up on the main output, further compromising signal purity.  I
>> suggest using a 20 dB pad between the rear panel output and any
>> counter to minimize this.
>>
>> The 11710B works reasonably well (I use them with 8640Bs to get below
>> 400 kHz), but the internal crystal oscillators are a bit noisy so the
>> mixed output has a poorer noise floor than the 8640B and also has
>> more phase noise, if you are doing anything where phase noise is a
>> concern.
>> As Al noted, the "B" version makes a voltage control input available
>> on the back panel.  If you have the HP 8655A reference/phase detector
>> (or build something similar -- the originals were rare even in their
>> own day), you can use this input to lock the 8654B to an external
>> standard, at the price of quantized frequency steps.
>>
>> Best regards,
>>
>> Don
>
> Okay, Don.  I'm just doing simple IF/RF alignment so I guess it's probably 
> good enough for my purposes.  The 8655A is the counter and not sure how 
> much extra noise it would add to the mix.
>
> Still might just go with an 8640B.  The 11710Bs cost almost as much as a 
> good 8640B.
>
> Thanks for the info,
>
> Barry - N4BUQ
>
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