[Central-Electronics] 100V RF phase/Null adjustment touchy

[K6JEK]

That idea with the pots is a good one. I may do that. These are way  
too touchy.

What do you mean the 9 MHz coils were spaced too far apart?

Sent from my iPhone

On Mar 23, 2010, at 7:13 PM, "Jim Candela" <jcandela at prodigy.net> wrote:

> Jon,
>
> I never had a 100/200v, but I do own 20a's. On one unit I took the  
> carrier null pots and replaced them with a lower value with series  
> resistors on each end to get the same resistance as before. Since  
> the original pot was not perfectly at the center, I had an offset on  
> the fixed resistors such that the new pot was close to center. The  
> result was a smooth carrier null without the need to stare at it in  
> order to keep the null at optimum..
>  On another 20a, someone installed wire wound 10 turn pots. That was  
> a debate on this forum back several years ago, using WW pots in a 9  
> Mhz phase shifter. I had other troubles so I took the WW pots out.  
> Those WW pots did a fine job though, and my removing them was  
> because I was stumped. The actual problem was the two 9 mhz coils  
> were too far spaced away from each other. Not my first guess..
>
> Jim
> WD5JKO
>
> ----- Original Message ----- From: "k6jek" <k6jek at comcast.net>
> To: <central-electronics at mailman.qth.net>
> Sent: Sunday, March 21, 2010 7:44 PM
> Subject: [Central-Electronics] 100V RF phase/Null adjustment touchy
>
>
>> I've been fooling with the 100V.  The carrier suppression was  
>> lousy.  The usual parts are relatively new and closely matched so I  
>> figured what the heck, try the RF phase adjustments.
>>
>> Using a FLex radio as a spectrum analyzer, with the mod caps out to  
>> keep audio from confusing the issue, I adjust those two RF  
>> transformers, tweak this one, adjust null pots, tweak that one,  
>> adjust null pots.  I was able to make a huge improvement, from a  
>> miserable -20 dB to -60 dB.  Pretty good, huh?
>>
>> Except the way this thing is adjusted, the null pot adjustments on  
>> the front are super touchy.  The slightest nudge of the knob and I  
>> mean miniscule nudge and I lose 10 dB of carrier suppression.
>>
>> What have I done wrong, and what should I do to fix it?
>>
>> Jon
>>
>> ______________________________________________________________
>> Central-Electronics mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/central-electronics
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Central-Electronics at mailman.qth.net
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>