Local oscillator accuracy, stability (drift) and, more so as you get into
the higher bands, phase noise are big considerations. I find that for my
homebrew transverters on 50 through 432 MHz, a regular free-running crystal
oscillator properly calibrated is sufficient. On the bands above that, all
my LO's are phase-locked to a high-quality 10 MHz OCXO. My favorite method
of phase-locking is with the low-noise phase-locked VCXO design of John
Stephensen KD6OZH or a variant of that circuit. My 47 GHz station is pretty
good; there is a little "wobble" in the LO frequency but it's probably not
more than 20 Hz wide. For that I use the LNPLXO circuit driving a Frequency
West brick with output in the 11 to 12 GHz range.
Receive sensitivity and noise is the other thing I consider really
important. I have homebrewed a lot of low-noise preamps. For some devices
and circuits used in the microwave transverters, they were a little
unstable unless I added microwave-absorbing material to the inside of the
lids.
Transmit power is whatever you can manage. I generally enter contests as a
Single-Op (QRP) Portable. So I run under 10 watts on the lower bands, 3
watts on 10 GHz, 1 watt on 24 GHz and maybe 100 microwatts out of a basic
DB6NT mixer board on 47 GHz. My 78 GHz (a work in progress) will also be a
handful of microwatts.
73, Zack W9SZ
On Wed, Apr 25, 2018 at 2:20 AM, N1BUG <paul@n1bug.com> 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
> _______________________________________________
> VHFcontesting mailing list
> VHFcontesting@contesting.com
> http://lists.contesting.com/mailman/listinfo/vhfcontesting
>
<https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon>
Virus-free.
www.avast.com
<https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link>
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
_______________________________________________
VHFcontesting mailing list
VHFcontesting@contesting.com
http://lists.contesting.com/mailman/listinfo/vhfcontesting
|