Just a quick post to share info about a good 9 MHz crystal sold by
Mouser Electronics.
I last purchased
batches of crystals for xtal IF filters back in 2014. Since then,
I’ve bought various 1 off xtals for micro controller clocks, but
these were never critical parts. Now in 2025, I felt a freeze frame
effect – a huge difference – Crystals cost more, less IF choices
seem available; and now, the mini- HC49 or SMD versions seems more
popular than the full size HC49 variants. All this makes sense in
a SMD/digital world.
Further, I randomly swept some of
the smaller sized rocks that I had ~recently ordered and I seemed to see more
spurs, plus, low Qul (< 70K in 3 cases ) -- at least in the
handful of crystals that I tested.Your own results may vary.
I've
already wrote about worsening
access
to xtals
for filters
in
some areas of
the world
–
we are pampered with Mouser and Digi-Key in
North America.
In parts of Eastern Europe where
I have a couple of contacts,
some analog builders find 3 or 4 xtals that are the same frequency inside a
bunch of old
computers and desolder them. Forget about frequency matching multiple xtals –
that’s for “ rich people”.
Today, If
you count currency exchange, shipping and perhaps tariffs, this rings
even truer. The days of ordering a batch of 35-40 crystals to make "1 good“ crystal filter seems a costly adventure for some builders.
I wanted to ply a specific 9 MHz crystal made by IQD - their 449-LFXTAL064523BULK (Mouser Electronics number). I wanted a maximum of 3 crystals in my filter – also 1 for the BFO. I prefer less poles – plus also a BW of 400 - 500 Hz for my CW receivers. I detest aural ringing from group delay in my xtal filters.
In my active audio filters, I now choose a Bessell response to get a maximally flat group delay to give you some added context about my preferences regarding filter group delay.
IQD 449-LFXTAL064523BULK
How did I learn about this particular crystal? On his website, Wes has pdf files on how to make crystal ladder filters. 1 of them is a file about making simple 9 MHz crystal filters – he actually relaxes a little bit on the equations/math for newcomers on this file -- and it’s a great file. Thanks Wes!
The 9 MHz crystal Wes uses on this paper is this particular Mouser part: 449-LFXTAL064523BULK . When I ordered them on Feb 5th – they had only 3 in stock !!! My xtal filter was made from those 3 crystals that arrived 2 days later.
I also had other IQD (Wurth Electronics) crystals in other frequencies ordered from Mouser long ago including 7.68 MHz, 7.3728 MHz, 4.9152 MHz and 2 other frequencies, so I felt confident IQD crystals are both suitable + economical for RF experimenters like me.
Before I measured my xtal parameters using the G3UUR method plus hand calculations. I exactly copied Wes’ simple CW filter capacitor values as a curious experiment. Wes only showed simulations – however, from experience; software can not simulate all the stray capacitance from the IF amp, coils, connectors, etc. But it’s close enough for jazz.
Above — Snippet of my IF stage within my receiver. Filter input /output Z = 50 Ω .
Above — Sweep of my 3 xtal filter. Span = 40 KHz Bandwidth = 449 Hertz due to different crystal parameters than the source article - but still OK for me.
For 3 random crystals (unmatched) – I think it looks OK. The losses are over stated in my sweeper due to extra attenuator padding -- I carefully measured the filter insertion loss at 3.89 dB for these 3 random, unmatched crystals.
Above — Sweep of my 3 xtal filter. Span = 10 KHz
Back Order
At the time of my order, I also back ordered 20 more 449-LFXTAL064523BULK crystals.
Mouser evidently orders these crystals in batches of 1K from their supplier. I feel glad that IQD (Wurth Electronics) are still making them. I received these 20 back-ordered crystals last week & measured the Qul of 3 of my xtals which averaged ~135K. Good enough for CW and SSB filters alike.
Curiously, when my xtals arrived on March 11, Mouser had 972 remaining in stock. When I checked again about 1 week later --- they had 0! Mouser seemingly ordered another 1000 from the factory and they will arrive near the end of April. I wonder how long this stock will last?
If you need xtals for IF filters in future projects – perhaps now might be a time to buy some?
Best!
Thanks Todd. I recently was making crystal filters at 24.9 and 25 MHz. Very difficult to get flat topped passbands at these freqs, but the rounded tops don't seem to make much difference in performance. Another thing I noticed: the smaller (low profile) crystals seem to work better, both in the filters and in the BFO/carrier osc. I don't know why, but I had trouble with the taller rocks. When I used one in the BFO the oscillation was kind of eratic. I switched to another similar (tall) rock and the problem disappeared. 73 Bill N2CQR
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