[HBR] Tracking

[Walt Hutchens]

Brian said:

> Has anyone tried doing an end run around the tracking problem by having
> separate capacitors for RF, LO, and Mixer, and putting up with a lot of knob
> twisting in exchange?

It can be done that way, but why?  Tracking a three-tuned circuit
receiver has been done by literally millions of people and anyone on
this list is certainly able to learn how.

It takes a bit of patience and two or three rules of thumb but that's
about it.

1. Built an established design first -- or at least use the front end
from an established design.  That way the tuned circuits will be very
close to right without anything more than following directions.

BE FANATICAL about following the directions for making the coils. That
is the easiest and most common place to go wrong. Even if you don't
have the right forms (almost nobody does these days!) you can still
get close to the diameter and wire size and with the right number of
turns and connections you will be within the range of adjustment.

If the design you're following give directions for adjustment then
follow those. If it doesn't then do this.

2. Get the oscillator calibrated or tracked using a counter or
continuous coverage receiver. This is done as follows:

a. Set the tuning cap to the high end of the band and use the
(parallel) trimmer to get the frequency right.

b. Set the tuning cap to the low end of the band and adjust the coil
to get the frequency right. If this requires the tuning cap to be
fully meshed, increase the inductance a bit (push the coil turns
together slightly) so less tuning cap mesh will be needed while if the
cap is too far open, reduce the inductance.

Repeat 'a' and 'b' until you're satisfied. After a couple of cycles
you may find that overshooting the adjustments somewhat, saves time.

3. Now feed in a signal and adjust the antenna and RF coils in the
same way for the strongest signal at each of those two points.

If something doesn't seem to work, then figuring out why becomes your
next step.  This list will help -- nearly everyone here has been down
all the blind alleys!

Walt
KJ4KV