[ARC5] need advice on Tx tracking adjustment

Sun Aug 21 17:56:28 EDT 2016

Hi,

Maybe my message about the tuning didn't make it to the list. Your 
tunning *range* is too short. On many radios you adjust that with the 
low frequency adjustment and then zero at the high frequency end. I didn't
  re-read your original post but sounds like what is being described in 
your manual. When your radios is set for 3.0 mc and is actually 3.004 mc 
then use the low frequency part to put it on 2.998. Then use the high 
frequency adjust ment to make 3.000. Reset to the high end and check 
there. Make it read 4.0 and make it so with that high freq part. This is 
like the instructions on shampoo. Rinse. Repeat. work back and forth 
until you get it or until you go crazy.

Some of those old radios are very close and none of them are going to 
track the nearest milliherz. Most of the instructions tell us to use a 
high frequency setting near about 80 per cent (3.8000000 mc in your 
case) and a low frequency setting of about 20 per cent (3.200000 in your 
case). The idea is to distribute the nonlinear tracking 'error' over 
more of the range so there will be less error from tick to tick across 
the range. The tuning cap should probably not be banging the stop at 
either end.

Good luck with your project.

On 08/20/2016 09:34 AM, J Mcvey via ARC5 wrote:
> when I said 4khz end to end I meant that if I tune the dial at the top 
> end (4 MHZ) to be dead on(zero beat) , then go all the way down to the 
> low end (3mhz), I will find 3 mhz reading more like 3004 khz on the 
> dial.  Obviously, the error progressively gets worse as I tune down 
> the dial until it culminates in the 4khz error at the bottom end.
> This what I mean by dial tracking. It is said to "track" when the dial 
> frequency and the actual frequency match exactly.
>
> Bottom line; There is only one combination of L and the variable C 
> where the frequency will correspond with all the tick marks on the dial.
> I was wondering what is the best way to proceed in finding that 
> perfect combo.
>
> I think the components have drifted over the years, but still well 
> within tolerance to be tuned properly since the max error is only 4khz.
>
>
> On Saturday, August 20, 2016 2:45 AM, Leslie Smith 
> <vk2bcu at operamail.com> wrote:
>
>
>   Hello Jim,
>   I need to check my understanding.
>   Do you say that at every point on the dial the frequency is "off" by 
> exactly 4.0kHz.
>
>   You used the words, "end to end" - and these words give that idea.
>   If that is the case, the dial itself is out of calibration.
>   The set itself is accurately set up.
>   If so case there should be a procedure to leave the oscillator tank 
> components untouched and simply adjust the dial mechanism.   That's my 
> take on this.   The problem seems to be related to the first point you 
> made - that the locking screws were corroded in some way.
>
>   However, my conclusion depends on my assumption - and that may be wrong.
>
>
>    BW & 73 de Les Smith
> vk2bcu at operamail.com
>
>    o-o-o
>
>
> On Sat, Aug 20, 2016, at 14:21, J Mcvey via ARC5 wrote:
>> This particular BC-696 was supposed to be "government refurbished" in 
>> 1953. It was on a single  rack wrapped in heavy plastic.
>> The only problem was that whatever they used to clean it was not 
>> properly rinsed, so over the years in the bag, it ate the lock knobs and
>> some of the case screws!
>> Fortunately, the innards were OK.
>>
>> The problem is that the tracking is off 4 khz from end to end. The 
>> specs say that it should be within 200-300 cycles.
>> The osc trimmer was nearly all the way out of mesh, so I didn't have 
>> enough adjustment to bring it up to where it needed to be.
>> I set the trimmer at 50% and adjusted the main osc cap. That got it 
>> on frequency THERE, but the tracking is still go good
>>
>> This stuff is notoriously tricky , so I consulted the manual.
>> Page 57 (of manual-PDF page 71) describes the process , but is very 
>> vague, talking about "changing the dial to the other side of the 
>> lowest frequency mark at a point about
>> 1 1/2 times from that mark as observed..."   WHAT???? This make no 
>> sense to me!
>> Can someone explain what they mean in a coherent way?
>>
>> Is it:
>> 1) adjust to highest frequency (done!)
>> 2) next,adjust the TX dial to find where the lowest frequency is 
>> shown on the dial.
>> 3) if not tracking,note where the lowest frequeny is shown on the TX 
>> dial, and move the TX dial 1.5 times the error in the opposite direction.
>> 4) adjust that new point to the lowest TX frequency with the osc coil.
>> 5) Move the TX dial to properly indicate the lowest frequency
>> 6) Use trimmer to tune to the lowest frequency.
>>
>> I reworded it to accommodate modern test procedures using a frequency 
>> counter instead of "zero beat"
>> Does this sound about right?
>>
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