Posted by
Ken G3WCS on
Apr 09, 2005; 11:33am
URL: http://elecraft.85.s1.nabble.com/Elecraft-XV144-and-XV50-TX-Noise-and-birdie-tp376803.html
Hello all,
A few months back I put together the XV144 and XV50 transverters. Both
work fine but following some comments from very local stations I decided
to make one or two checks.
I am comparing these tranverters with my own original 144Mhz transverter
which I built about 15 years ago.
With no input to either transverter but with the input terminated at 50
ohm and with a resonant antenna connected, listening on another receiver
with an antenna connected reveals quite a high hiss or mixing noise when
the PTT line is operated. This happens on both the 50 and 144 Mhz
transverters. If I operate the PTT line of my old home brew transverter
there is no such noise or if any it is very much reduced. I am sure the
hiss (phase/mixer noise) is many db down on the normal output level but
it is nevertheless much greater than my original home made unit.
Secondly, and somewhat more worrying is a drifting birdie that both the
XV50 and the XV144 produce. Once again I know these are many db down on
the normal output but the 144 Mhz birdie is of sufficient strength that
a station 15 miles away heard it whilst trying to work an EME QSO. It
drifted across the frequency he was using. On my particular transverters
these birdies occur at about 50.130 Mhz on the XV50 and about 144.140
Mhz. They seem to drift LF during TX and at a rate of about 10 Khz in 5
minutes.
I wonder if anyone else has made any observations and come up with a
cure. I all other aspects the transverters are excellent and totally
stable. Indeed, the 144 Mhz version is fitted with a crystal oven.
I know there was a thread on here a month or two back regarding phase
noise being heard by stations within a 20 Km radius during high levels
of 144 Mhz activity.
Has anyone else got any more comments or observations to make. I know
that my observations are not exactly 'scientific' but there are made by
comparison with a different transverter which does not exhibit these
problems. During all these tests the transverters have had their inputs
and outputs correctly terminated with no 28 Mhz drive source connected.
Sorry for the long waffle. Any comments most welcome.
Best 73,
Ken G3WCS.
--
Ken G3WCS
IO83rh : Cheshire : NW England
(+44) (0)870 765 1632 (home)
(+44) (0)7733 400 950 (mobile & sms)
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