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LA8AK > TECHNI 06.11.95 04:23l 39 Lines 1474 Bytes #999 (0) @ WW
BID : 25042_LA9K
Read: GUEST
Subj: Drake R-4C VFO leakage problem.........
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Sent: 951105/2238Z @:LA9K.XND.K.NOR.EU #:25042 [Kr.sand] FBB5.15c $:25042_LA9K
From: LA8AK@LA9K.XND.K.NOR.EU
To : TECHNI@WW
One problem experienced trying to fit a heathkit scanalyzer to this receiver
was that it is a strong 5MHz signal (VFO) - only to close to the 5.645MHz IF
this overloads the scanalyzer - in fact it is 60dB stronger than an S-9 signal
so a ringmixer was tried for the scanalyzer, but still not very much useful.
the problem was traced to the pre-mixer function, a small amount of 'VFO-
signal' seems to be there in the pre.mixer output signal, but this is not
really true, it is there only as a sideband to the desired signal
the extra sidebands (Xtal-Osc +/-VFO frequency) interfere in the RX mixer
V2 and result in a VFO signal at the mixer output.
I tried to use ringmixer (SBL-1) with 6EJ7/EF184 buffer, but unwanted signals
just increased, so I left everything as original!
The scanalyzer idea is left.
Another problem is 'BFO leakage' - the problem exists almost as bad with or
without change of product detector. I believe it stems from birdies
from second mixer, it seems to be a variable problem, some mechanical effects
causing variable degree of this signal.
Lift one front corner of receiver and let it fall down hard, sometimes this is
necessary to restore some other problems, sometimes it helps against
BFO leakage.....
good luck!
73
jan-martin
ps
serial number of my rx is 22077, once it was silent, coil wire inside an IF
xfmr was broken. Philips EF184 seems to be more silent than the original 6EJ7
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