[Collins] Split Mode

[Dr. Gerald N. Johnson]

On Tue, 2006-02-14 at 23:52 -0500, David Thompson wrote:
<SNIP>
> The Drake and Heath equipment came later and standardized on the 500 kHz
> tuning ranges.  Before then 200 was the standard with Collins, Eldico, and
> the KW series from the UK.  One additional limiting factor was the receiver
> preselector tuning.  So even if you had a split from say one end of the
> tuning range (say 14100 to 14280 as W0MLY used on his African trip in 1962).
> The signals on either end of the split were normal but reduced quite a bit
> as the preselector needed to be peaked at the other end (the receiving end).
> Dick reported S9 signals became S4 to Collins Engineers hoping for a fix.
> 
> 73 Dave K4JRB  Be there done that.
> 
W0MLY liked to tell everyone his way of doing things, but he was so
gruff that many didn't listen. He was less gruff once drunk under the
table but I never tried to be successful at that.

I doubt if the factory would have been willing to lower the Q of the
preselector tuning because that was the only way of achieving image and
half LO (on the high bands) rejection. Perhaps the design could have
included more coils tightly coupled for better distant rejection and a
flatter bandpass (and likely the LO coil was a critical as the RF coils
or even more the limit, since mixer gain goes as LO level). But tracking
double tuned over or critically coupled bandpass circuits from 3.5 to 30
MHz is a whole lot harder than tracking single tuned circuits.

As a practical matter, if MLY had wanted to consistently operate the
split he probably could have tuned the preselector to the desired
receiving range and then while transmitting peaked the oscillator
trimmer to have achieved a better result with the split, at least a bit
more gain for both situations. Or simply left the preselector in the
middle of the range instead of peaked on either frequency. And it
wouldn't have taken much time to have loaded the coils with 10 or 22 K
shunt resistors to lower their Q (and gain) to increase the bandwidth.

The farm that MLY raise towers and large PAs on is now owned by N0NI and
has a large number of towers for a contest station way out in the
country near Rippey, Iowa.
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer