EMRFD Message Archive 1675

Message Date From Subject
1675 2008-05-24 21:39:12 John Shepherd 100 MHz Crystal Source
I'm half-way through building the W7ZOI Spectrum Analyzer, as described in
Section 7.8 of EMFRD. But I'm stuck on the 100 MHz second oscillator-mixer
module. The 100 MHz. crystal, that came with the kit, seems to be
inoperative. If I replace the crystal with a 51 ohm resistor, I do get an
unsteady 100 MHz. signal out of the mixer. But when I re-insert the
crystal, there is no oscillation.

It's difficult to buy this "Thru-Hole" crystal. Digi-Key and Mouser don't
stock it. Manufacturers like Vectron and ECS sell through distributors that
aren't interested in small orders.

Can anyone suggest a source? Or does anyone have a spare in their junk box
that I could buy? I'd like to get two, and have one as a spare. I don't
think that the specifications are critical.

John Shepherd


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1679 2008-05-25 08:20:03 john lawson Re: 100 MHz Crystal Source
John, I experienced the same problem, however it was
NOT the crystal that was causing the problem. My
experience was exactly the same as yours! Here is what
I went through which may give you some insight and

After a bunch of parts changing on the PC board (FET,
caps, etc) I decided to drop my 100 MHz crystal in an
ugly circuit that I had built for 110 Mhz for the
alignment of the VHF band pass filter. After
readjusting the tank circuit to 100 MHz with a 50 ohm
resistor in the circuit and a VHF Freq. Counter, I
installed my crystal and it performed perfectly, This
ugly circuit was identical to the oscillator circuit
for the SA.

In communicating with Wes he told me that he suspected
the reactance of the 470pf bypass cap in the tank
circuit (C202) on the PC Board was the problem, if I
recall correctly. My 470 pf cap was a COG ceramic cap.
Try building the circuit ugly and see what you come up
with first. Once I found out that it wasn't the
crystal, I simply built my oscillator on top of the PC
board ugly with a few new parts, as I had ruined some
of the foil runs with some previous trouble shooting.
I then attached the output of the pad to the .01 cap
(C208) to the MAV-11. The oscillator then worked
perfecly. If you find it necessary to replace your
crystal, try International Crystal. I called a number
of crystal mfgs while I was trying to come up with a
solution. Int'l Crystal quoted me the lowest price in
total including shipping and handling. In the past
their quality and service to me has been outstanding.
I hope this helps, John K5IRK

1680 2008-05-25 08:20:06 wimmie262000 Re: 100 MHz Crystal Source
Here in the Netherlands there is a small supplier that has a 3rd OT
crystal for 1.50 Euro. But they probably only ship inside EU.
http://www.vandijkenelektronica.nl/ (site is in Dutch, sorry).

A more expensive guy that does ship internationally is Barend Hendriksen
There is a minimum order, but he has more RF stuff you might find

If absolute accuracy is not required, perhaps you can simply try a
20MHz crystal. Occasionally some common (computer) crystals have such
a low series resistance that they still work well at 5th OT. It is
likely to be a bit off from 100MHz but that might not be a problem for

As an example I managed to get a cheap 17.7 Mhz crystal to work at
about 125MHz in a Butler oscillator for a DDS clock. That is at it's
7th OT.

Joop - pe1cqp