[R-390] the saga cont. part 3

[ka9egw at britewerkz.com]

Sooo...[deep breath]...I found where the one leftover green screw went and
it didn't even require major surgery; just had to get to the right setting
on the MC CHANGE knob to reach through the holes in two different
overlapping gears...it was the third screw for the crystal deck.  I can't
for the life of me find any more holes to plug screws into, period, that
aren't filled by through-panel flatheads, so...I can only assume the
remaining half-dozen-odd 6-32x3/8 are for holding down the utah cover...even
if I don't remember taking it off HI HI.  Two of them may nor even be 390A
screws because they're rusty and IIRC 390A hdwe is all s/s?

So...I did the audio sensitivity measurement as suggested by feeding
150uV/30% into the IF chain and verifying the audio out went from measured
>19V to <.6V when modulation was removed.  Good deal, eh?

Onwards to rf sensitivity measurements...feed the unbal ant in ~1uV at 30%,
tune sig gen off freq, peak ant trim on noise, set local gain for ~1V across
a 600 ohm load, [ok, an 8-ohm speaker fed through a 600:8 xformer and read
the ac voltage on the primary], tune sig/gen back to freq and measure amount
of sig/gen output needed to raise audio out to ~3.2V from ~1V [the "~" is in
reference to the fact I haven't yet demothballed my analog VTVM and the
digital one bobbles a bit].

Sanity check: 3.2V:1V = 10dB, yes?

That being the case, worst-case sensitivity for 10dB S+N/N at 1kC 30%
modulation and 4kc IF B/W [checking 100kc in from each end of each 1Mc
segment] appears to be .51uV @ 11.1Mc.  Of the bands I consider important,
namely .5-1, 1-2, 3-4 7-8 and 10-11 [BCB, 160, 80, 40 and 30, in other
words] worst case is just a froghair under .3uV.

I have yet to go through the RF deck alignment, crystal filter
neutralization, etc.  I believe I will hook the sweeping voltage of my old
sweep gen into the scope's external sweep input and the scope's veryt input
to IF OUT so I can see the actual bandwidth plot on the xtal filter right
there on the CRT...haven't done that since my old HQ-129X back in about '79.

Anyone care to comment on similarities and differences between the HQ-129's
single-crystal filter and the 390A's?  I note the 390A has no "phasing"
control on the front panel...

Anyone know where I might find a manual for my Measurements Corp 82 sig/gen?

73 de KA9EGW