[R-390] R-390 alignment questions

[Cecil Acuff]

Thanks John, Wally, Don and Bob...

        I feel kinda silly....after coming back in from the shop a few 
minutes ago and finding out exactly what John has described while out there. 
I didn't read the book close enough and use my brain.  I knew I was doing a 
balance adjustment and by inputting an in phase signal on both inputs it's 
going to take a lot more signal....I also didn't notice I was tuning for a 
"NULL"....

That's what happens when you stay in the shop till all hours of the 
night....hate to give it up knowing you have to go back to the real world in 
the morning...

Anyway...after inputting a signal into the balanced input with one side 
referenced to ground only minor alignment to the first set of coils and caps 
was required then the balancing was performed...

All is well now....sensitivity is still in the .3-.4 uv range 
overall...slightly down from before but there is another set of coils in the 
signal path...so selectivity should be better.

I spot checked the other stages but found everything on peak...so I am 
calling it done.  Antenna trimmer now peaks at the center for the input 
impedance being used so it looks like it's right...

Thanks again for the help....

Gonna have to start giving it up a little earlier....

Cecil....


----- Original Message ----- 
From: "John KA1XC" <tetrode at comcast.net>
To: "R-390 reflector" <r-390 at mailman.qth.net>
Sent: Tuesday, October 12, 2004 9:40 PM
Subject: Re: [R-390] R-390 alignment questions


>> I thought I would go back and input a signal on the balanced input 
>> through
>> two 68 ohm resistors and set the balance trimmer for each band only to
> find
>> the radio pretty much deaf.
>
> Cecil,
> for doing the balance adjustment that's perfectly normal. I've found that 
> to
> get a hearable signal for nulling I need to set the generator output 
> several
> orders of magnitude greater. (Think about it, if the input balance was
> perfect you'd never hear ANY common mode signal).
>
> RF alignment is best done using the low-z balanced input with one side
> grounded (thus making it unbalanced) and connected directly to the signal
> generator output. Connecting a 50 ohm sig gen output to the hi-z 
> unbalanced
> input will work of course but you're *really* loading down the front end
> tuned circuit and probably getting a much broader peak during its 
> alignment.
>
> John
>
>
>
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