The Toko CBT Helical resonator and the 10.7 Mhz ceramic filter
are both available from Digi-Key. I have most of the parts for
that project, just never got around to building it. It should
cost considerably less than $100 today.
The author, Helfrick, also wrote several articles for QST about
building spectrum analyzers from CATV tuners.
Another source for spectrum analyzers is Science Workshop, at
<http://hoflink.com/~mbarlowe/>, who have an a-la-carte kit
which, for around $200, is supposed to give you a 5 Meg to 900 Meg
analyzer adapter, which you then hook to your scope.
I have my suspicions that the AVCOM analyzer, offered for $1500 or so
in the back of QST, is nothing more than one of these kits, attractively
packaged in an inexpensive oscilloscope chassis.
As far as surplus commercial units go, there seem to be three grades.
The big old clunker grade, exemplified by the HP 121T mainframes with
plug-in tuning units. I suspect that if you can find a working one
at a bargain price, they're OK, but no prcision frequency readout and
perhaps custom components inside that are impossible to replace.
The second grade is the HP 8590 type. At first glance, these $10,000
list portables appear to be attractive, with on-screen frequency display
and microprocessor control. They sell on the surplus market for around
$2500. I actually had a chance to pick up one of these and I turned it
down. Reason being that, while they appear to be synthesized units, they
are in fact running open loop, and the displayed center frequency can be
as much as 5 Mhz off! I thought I could probably build something cheaper
that had the same features.
The third grade is probably the one I'd buy if one came along. The HP 8591
and later units start around $12,000. They're current production
portables.
The later HP 8568 bench models are $70,000 and up. Not much chance of one
of these falling into my lap. I have one at work, though, and it sure is
nice.
There is a neat alternative, though, and I have one of them. They're
called
service monitors, and they come in various shapes, sizes and qualities.
Mostly used by the land mobile and commercial radio repair places, the old
ones are becoming less useful as trunking and digital modes begin to
take over. You may find one of these 30 Mhz to 1 Ghz synthesized signal
source,
receiver, oscilloscope and spectrum analyzer combinations for anywhere
between $2500 and $10,000 (or free if it's broken!). Mine's a Cushman
CE-4B,
and it's a real clunker. No spectrum display, but it does generate and
demodulate AM and FM and has a neat little scope display. I got it for
free
and fixed it. Bad gate in the reference divider chain. Cost me $50 for a
manual.
Thanks to Steve, KD1JV, I have a 0-100 Mhz spectrum analyzer/scope adapter,
which is my current building project. It's enough for me right now, but
I think Science Workshop is going to be getting an order from me.
Regards,
Peter, KA1AXY
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