LO drift is a big problem. One of the underlying reasons for the results
you have seen is the quality of the crystals that are being supplied to
the transverter manufacturers. Parts that were tested and specified
originally are showing up in later deliveries with just awful
performance. It is hard for small companies with small production runs
to get anything resulting in repeatable characteristics without
unmanageable lead times. Note that just about every US quartz crystal
manufacturer is no longer in business. I was given a small frequency
counter as a Christmas present. After a few months, I noticed that the
timebase had shifted by 4 kHz when measuring a signal at 2 MHz. I
thought a jump like that was impossible with Quartz. No telling what
was left inside the crystal housing to cause it. My suspicion is that
it was the General Tso's Chicken option. I just read the book _Crystal
Clear. _It is the story about ramping up to produce crystals for WW2
radios and how the Govt and manufacturers did it. There were many
pitfalls to overcome and quality issues to address. Almost all those
companies are now gone.
73
Dave K1WHS
On 4/25/2018 7:20 AM, N1BUG wrote:
One thing I didn't see on your list that always concerns me is LO
drift. Drift can be a problem for any weak signal work, say a long
haul CW sked during a contest. If you want to do some of the digital
modes it can become a critical issue, even a show stopper.
Since I can neither afford nor get my head around the complexities
of GPSDO locking, I am always concerned about crystal oscillator
drift in transverters. Usually I do the best I can to build and
install some type of crystal heater... with mixed results over the
years.
Sometimes I find things that surprise me. Last summer I measured
drift on two 1296 transverters: a relatively ancient UHF Units and a
relatively newer but not current generation DEMI, both as yet
unmodified. Over a temperature range that caused the DEMI to drift
over 6 kHz, the UHF Units moved just a bit over 200 Hz! I know which
one I will be using if I ever get the rest of the stuff together for
1296.
Paul N1BUG
On 04/24/2018 10:31 PM, Patrick Thomas wrote:
Hey all,
Subject more or less says it all... I guess better sensitivity,
lower noise, better selectivity, and better linearity are the
essentials in vague and relative terms, but what attributes do
you look for in a REALLY GOOD transverter?
Or for those who have gone further into making them... what
components, construction techniques, etc., make a difference?
Partly this is a question I hear a lot and only have a vague
notion of how to answer other than "obviously the expensive ones
are better... somehow." :)
And partly it is a request for topics for self-guided
study/experimentation as I attempt my own homebrew projects.
Many thanks,
Patrick - KB8DGC
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