Chuck -
First ... "It is normal for the gain of the receiver and transmitter to
vary slightly with the position of the transceive switch."
That said, the basic fact is that the INJection and the CARrier
OSCillator signals are what is patched between the two units. The CAR
OSC signal is at 5.645 MHz, and is not likely to be a problem as it is
the same on all bands. The INJ signal however, is 11.1 MHz above the
dial frequency, and on the higher bands is in the 30 - 40 MHz range.
The _capacity_ of the INJ cable is critical, and the original cable
has a TOTAL capacity of 60 pF, including connectors. This capacity is
connected across the tuned circuits of the input and output amplifiers,
and so has a greater effect as the frequency goes up.
My _guess_ is that:
1. The 160M band differential MAY be an effect of the narrower bandwidth
of the T-4XC on the higher bands. The original version didn't like to
go below about 1850 kHz. Changes were made in the second version to
stretch this down to 1800. Question. When you recorded the 5 dB
difference were you well below 1800 kHz?
2. The other bands WILL vary around whatever band and frequency you did
your alignment on. When this occurs, are you able to return the gain to
nominal by peaking the PRESELECTOR, or RF TUNE controls? BOTH controls
must be peaked, and be close to each other in frequency.
After 50 years of servicing and using these radios, I have yet to find a
pair that did NOT vary from RCVR to XMTR control in TRANSCEIVE to some
extent. As a matter of practical fact, 5 dB difference in a received
signal strength is almost NEVER noticeable due to the excellent AVC.
One last thought. IF your Preselector or First Mixer tubes are weak,
making the PreMix signal level marginal, it would have an effect on this
problem.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs
<www.k4oah.com>
Chuck Pool wrote:
Hi to all:
When switching between RCVR and XMTR, by using the "Transceive" switch
on the T4XC, received signal strength remains constant (the same) on
some bands while others bands produces a drop or gain is signal strength.
I am using the calibrator as the received signal with the AGC set to
fast, 50 ohm dummy load selected then antenna selected for comparison.
Some times it is the XMTR that has higher received signal strength.
Some times the RCVR has stronger received signal strength. And, some
times both rigs have identical received signal strength when selecting
between RCVR and XMTR, via Transceive switch on T4XC, on different bands.
i.e. 80 meters has produced no difference in received signal strength
when switching between RCVR or XMTR.
i.e. 160 meters produces 5 db stronger received signal strength when
T4X-C "Transceive" switch is set to RCVR. The received signal
strength is 5 db less when XMTR is selected.
I have tried different types of injection cables, went through a
careful alignment of both radios (while both were connected together)
and still there is no uniformity between the bands in received signal
strengths when switching between RCVR and XMTR.
Why is this?
Any suggestions on how to obtain uniformity in received signal
strengths on all bands when switching between RCVR and XMTR via T4X-C
"transceive" switch?
73,
Chuck Pool - AA5WG
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