[R-390] R-390 alignment questions

[Bob Camp]

Hi

The unbalanced input bypasses part of the front end selectivity on the 
radio. The balanced input is the preferred input. Some of the coils are not 
aligned when you only do an alignment with an unbalanced input. That's 
probably what happened with your radio.

Most people run the radio with one side of the balanced input grounded. The 
antenna hooks to the other side of the balanced input.

No matter how you run the radio you need to align the radio the same way you 
use the radio. If you run a 50 ohm antenna then align the radio with a 50 
ohm source. If you align with one impedance and then run with another the 
difference should not be dramatic, but it will be noticeable. Best guess is 
that you would see maybe a 30% change in sensitivity.

    Enjoy!

        Bob Camp
        KB8TQ



----- Original Message ----- 
From: "Cecil Acuff" <chacuff at cableone.net>
To: "R390list" <r-390 at mailman.qth.net>
Sent: Tuesday, October 12, 2004 6:59 PM
Subject: [R-390] R-390 alignment questions


> Hey Folks,
>
>        I'm doing an alignment on an R-390\URR and I didn't follow the 
> instructions in the manual as to inputting a signal for doing the RF 
> alignment.  The IF alignment went slick...no problems. (followed the 
> book..HA!)
>
> For the RF alignment I put a signal into the unbalanced BNC cable that 
> attaches to the antenna relay directly to my 50 ohm input HP-8640B. 
> Seemed the logical thing to do.  The alignment went well and the radio 
> turned out to be quite sensitive on all bands...around .2-.3 uv for 10db 
> over noise. Performs excellently on the air as well.
>
> I am aware of all the cable leakage problems and what not...but the final 
> product turned out ok...
>
> 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.  Thought maybe the antenna switch was 
> bad....and I still have to check that tonight but I believe now that it's 
> more the way I aligned the RF deck.
>
> My questions are this....what input do most of you use when operating the 
> radio?  I know that going into the unbalanced input bypasses part of the 
> tracking preselector....but it sure is easier to get a signal into the 
> unbalanced input...especially since most of our antennas are unbalanced.
>
> If I realign as per the manual am I going to be compromising performance 
> on the unbalanced input to bring up the balanced input....or should I 
> expect better performance by including the additional preselector stage.
>
> Or maybe I have stumbled upon something....the radio seems to work really 
> good the way it was aligned?  Just can't use the balanced input.(no loss 
> here)
>
> I assume at this point the issues are the same...390/390A.  This is the 
> first time I have aligned the RF section of one of these radio's...(bet 
> you couldn't guess)
>
> I plan to go back and realign one band tonight and see what difference it 
> makes.
>
> I know using the 50 ohm generator is already a variance from the manual 
> since it specifies using the URM/25 and it terminates differently.
>
> Any suggestions are appreciated....R-1051's don't give me these kinda 
> problems....
>
> Cecil...
>
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