[R-390] Sync Detect Radio w/R-390A [warning sand word used in text]

[Roger L Ruszkowski]

Gentlemen?

What is the best way to couple the 455 for best S/N??

Pontifications welcome.

Great weekend to all!!

Tom N5OFF

---------------------------------------
Tom,

The 455 output in the IF deck starts as a 50 ohm source from the cathode
follower. The deck to back panel is 50 ohm connectors and 50 ohm coax.

I would carry that 50 ohms source from the R390 into the new sync
detector box. In side there I would go for a transformer match to the
higher input impedance of the detector circuit. Even if it is sand state
the input will be more than 50 ohms. I would go for a tuned IF deck
transformer and work the winding ratio to get close.

If you can not rework the transformer, Then find a load resistor for  the
secondary that lets the most power be transfered over to load resistor.
This is
where the voltage across the load resistor is largest and the transformer
will peak up a good 455 signal and by definition let out of band noise
be passed to ground.

An inter stage IF that matched 5-10 K plate to a 1 meg grid would only
match the 50 ohm up to 5 - 50 K. OK for a bipolar transistor. But still low
for a FET or tube. Then you couple off the load resistor with a small
cap to the still higher input impedance of the first active device.
The small cap and high impedance then looks like a scope probe monitoring
the signal at the load point.

Cheep broad band method would be as follows.
If the detector input is real high (tube grid / FET ) then you terminate
the 50 ohm coax into a 50 ohm resistor at the detector end and couple the
signal into the device through a small cap. Terminating the signal into
a good load keeps trash on the signal line (distortion SWR noise) down.
The small cap and high impedance then looks like a scope probe monitoring
the signal at the load point.

Could we pull the 5814 Diode detector, and replace it with a sync detector
plug in
9 pin thing. I forget what the other 1/2 of the 5814 does. A FET could go
in to function
as that triode.

Roger KC6TRU

P.S. I hurt my self working on my DX100 and have been told to just do not
be
working on anchors until I get over my tendinitis. This includes my solid
state
6DC6 tube. I can listen, but I have to crank the MC knob left handed. No
pulling
the receiver out of the rack and getting it up on the bench.