You have to consider ambient temperature as well as the straight warmup
drift. Any portable operation will make things worse as the transverter
adjusts to a changing ambient temperature. I run into this all the time
with a cold shack. I turn on the heat when and the room warms up along
with the transverter. You also need to exercise the PA as it is the
worst offender for crystal drift.
I would think you would be OK after 30 minutes, as drift is manageable
but definitely noticeable. I tried the same test with my rather old
DEMI transverter built in a large diecast housing with a 20 watt hybrid
PA on the opposite side of the chassis from the LO crystal. The drift
was about 10 Hz per TX sequence on JT65. When you stopped transmitting,
the crystal drifted upward during the receive cycle and would be 10-12
Hz higher the next time you transmitted. It worked OK but people could
see the drift. My solution was to install a styrofoam insulator around
the crystal to slow down any heat transfer. Then I mounted a small 12
volt fan on the heatsink just above the heat generating hybrid amp. That
really made a huge difference. Now my 222 transverter is very stable.
It wanders a few hz over many sequences, and people assume that I have a
GPS standard when they see how stable it appears. All I did to figure
things out was to transmit with the rig on the bench and monitor drift
with a good counter. I ran JT65 to get a realistic drift pattern. I
compare it to my GPS standard, so it is very accurate and does not
drift. Of course, then the problem becomes one of maintaining the
ambient temperature at a constant level. That variation will cause
additional drift. When temps are cold, I run the transverter for an hour
or so before the sked and try to heat up the room as well.
You could try a similar test with the Ukraine unit.
Dave K1WHS
On 4/16/2021 10:30 AM, peter h via VHFcontesting wrote:
0715pdt 16april2021
A number of us in SoCal have been using UT5JCW's 222MHz transverters with good
success on CW/SSB/FM from home and hilltopping/roving.
Tim, N6GP, wondered if they are suitable for use on FT-8.
Steve, WA6EJO, 'volunteered' to plot drift data on his UT5JCW 222MHz
transverter.
His results are tabulated below.
Steve, WA6EJO, did some transmit frequency stability tests using a GPSDO
referenced frequency counter.
Some of the drift may be due to the exciter, a TS2000X, but most is from the
Ukranian transverter.
From 2 to 3 minutes after power on it moved -227 Hz 3 to 4 minutes -103 Hz 4
to 5 minutes -64 Hz 5 to 6 minutes -45 Hz 6 to 7 minutes -27 Hz 7 to 8 minutes
-21 Hz 8 to 9 minutes -17 Hz 9 to 10 minutes -7 Hz 10 to 15 minutes +50 Hz 15
to 20 minutes +13 Hz 20 to 25 minutes +47 Hz 25 to 30 minutes +37 Hz
Do any experienced FT-8 users have any comments on possible use of the
transverters with data modes?
Thanks,
BT73
Pete, N6ZE
_______________________________________________
VHFcontesting mailing list
VHFcontesting@contesting.com
http://lists.contesting.com/mailman/listinfo/vhfcontesting
_______________________________________________
VHFcontesting mailing list
VHFcontesting@contesting.com
http://lists.contesting.com/mailman/listinfo/vhfcontesting
|