[ARC5] 400784741321

[AKLDGUY .]

> I completely rewound all three inductors in the receiver following the
article
> that Gordon White wrote some time ago entitled, "Command Receivers for
> All Frequencies", in which article Gordon described and listed the turns
on
> the coils that ARC came up with for THEIR early HF receivers up to 27 MHz.
>
> I used ARC's 27 MHz data, in fact, as the starting point for my coils.

OK, you rewound the coils on the basis of A.R.C.'s data.

Q is the reactance of either the inductor or capacitance at resonance,
divided
by the series resistance, which in this case is in the coil if we ignore
other very
small losses.

In my suggested modification (no modification of the coil) the Q is more
than
tripled by going from 7-9 to 28-30 MHz because the coil reactance more than
triples. The higher Q at the higher frequency means the selectivity curve
is the
same as at the lower frequency. The curve will be the same number of dB down
at the same frequency offset at both 9 MHz and 30 MHz.

There would therefore seem to be no good reason for taking turns off the
coils.
Why did A.R.C. use reduced turns? Probably because they were faced with a
too large value of tuning gang (no smaller gang available), so they used a
large
amount of **parallel** capacitance across the gang to reduce its tuning
range
and reduced the number of turns to compensate.

> Now I WILL say that your method would most certainly eliminate the
> necessity for removing any plates from the capacitors, but I STILL say,
that
> the inductances would have to be "adjusted" also in order to maintain
circuit
> "Q".

Yes, my method does eliminate the need to remove plates, but the selectivity
self-adjusts by virtue of the rise in Q as described above. A Q of 100 at 9
MHz
(easily possible) becomes a Q of more than 300 at 30 MHz, and the
selectivity
(percentage change) at both bands is the same.

I'd suggest that anyone contemplating modifying a 6-9.1 Mc/s receiver for
10m
try my suggestion first. You have nothing to lose. It's simple and
reversible. Use
very good quality capacitors and let them cool before evaluating.

73 de Neil ZL1ANM