Receiver alignment

Steve Harrison ko0u at OS.COM
Mon Mar 22 23:01:20 EST 1999

At 10:12 PM 3/22/99 -0500, Ed Tanton wrote:
>Hi George... get one of the large HP 608-D or 'F sig gens at a hamfest from
>someone who looks like you can believe him... in perfect condition (for
>something as mature as these are) they ought to be under (maybe even WELL
>under) $100... they are big enough that most sellers would just as soon not
>haul them around. But they have the frequencies you need, and a calibrated
>signal level out... plus modulation if needed.

Actually, 608s *should* go for around $25 from just about anywhere but
Surplus Sales or Tucker!

There are two frequency ranges, however, which you may not care about. I
don't have my manual here at home right now and can't remember exactly
which models had which upper limit; but I believe the 608A, B and D models
all had a high frequency limit of only 420 MHz. The C and E models went to
480 MHz (for sure the E as that's the one I have here). And I believe the F
also went to 480 MHz but also was capable of being phase-locked to an
external source. Worth keeping in mind if you might do any work on the
420-450 MHz band.

But the lower frequency limit on all of the 608 models was only 10 MHz
which you will also want to keep in mind since you won't be able to use
them to align 40 or 80 meter stuff or Heathkit IFs. 608s, with a warm-up of
several hours, can be VERY stable generators.

Naturally, try to get the manual with the unit.

Another unit worth looking for, if you don't mind spending more money, is
the URM223 (or is it the URM323??) which is the militarized version of the
HP8640 synthesized signal generator. The difference is that the URM does
NOT have phase lock capability, and that's why the cost is less than half
that of a good 8640. The lower frequency of the URM and 8640 is 500 kHz,
and my 8640B actually tunes down to 450 kHz which allows me to use it to
align older IF chains. Nice thing about the 8640 is the digital frequency
readout which is actually a frequency counter. I'm not sure whether the URM
has the counter; but the 8640 can be used as an external frequency counter
although the best resolution is only 100 Hz above 100 MHz and 10 Hz below
that. I've seen URMs going for $150, more often around $250-$350; the
cheapest I've ever seen an 8640 is around $500 and usually around $1000.
Either the URM, the 8640 or the older 608 series will be stable enough
without phase-locking if you let them warm up for an hour or more before
use. Some 8640Bs have an avionics option which is a reverse power
protection fuse; if you use it with a transceiver and accidentally key the
mike, injecting transmit power into the 8640 (up to 25 watts max), an
internal fuse blows, protecting the attenuator. Thus, you could find a
cheap 8640B with the avionics option and no RF output which just has a
blown attenuator fuse, easy to replace (although I don't know where you'd
get them!).

Fair Radio had some URMs for sale awhile ago; they still show up frequently
here and there. 8640s are less common. 608s used to be very common but now,
can probably be found holding up one end of someone's swap table who is
just as likely to leave it on the ground when they go home!

73, Steve K0XP

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