[ARC5] VFO dial alignment

[AKLDGUY .]

J McVey 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.*

The manual is clear about how to get the VFO to track the dial markings.

Section V
Maintenance
p. 43

Paraphrased:
Remove the top cover.
Set the dial to the highest calibration mark (4.0 MHz in this case). Tune
the transmitter for maximum power on VOICE  into dummy load.

Adjust the trimmer mounted on the VFO capacitor for zero beat against a
(4.0 MHz) signal source of very good accuracy. If zero beat cannot be
obtained, set the trimmer midway between its end stops, loosen the lock on
the VFO capacitor, and obtain zero beat by adjusting the VFO capacitor.
Then lock the capacitor shaft again.

Now set the dial to the lowest marked frequency (3.0 MHz) and check for
zero beat against a very accurate signal source. If there is an error, note
the amount (you reported 4 KHz). This error must be corrected by a proper
adjustment of both inductance and capacitance. ie. the coil inductance is
in error but the error cannot be corrected by adjusting it alone.

Adjust the slug in the VFO coil until the error is about 1.5 times the
former error, but in the opposite direction. That is, set the slug so that
the error is now 6 KHz low (2994 KHz). Now reset the dial to the 3.0 MHz
calibration mark and adjust the VFO trimmer capacitor for zero beat.

Check the high dial setting (4.0 MHz) again, and if not in agreement,
repeat the above steps. Check several frequencies in the band for accuracy
better than 0.04 per cent (1.4 KHz at 3.5 MHz).

It is desirable after this process that the VFO trimmer capacitor should be
near its mid-travel position, so as to allow minor trims during service
life without having to disturb the lock on the VFO tuning capacitor.
------

The process will be very easy with the aid of a frequency counter, and
won't need to involve resetting of the dial for the 3.0 MHz measurements.

73 de Neil ZL1ANM
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/arc5/attachments/20160823/b17572c2/attachment.html>