[R-390] Re: 390A tuneup

Mon, 30 Sep 2002 08:34:50 -0700

Tom,

I vote you move that receiver off the shop bench.

Roger.

                      "Tom Warren"                                                                                                     
                      <[email protected].         To:      <[email protected]>, "Roger L Ruszkowski" <[email protected]> 
                      com>                     cc:                                                                                     
                                               Subject: 390A tuneup                                                                    
                      09/29/02 07:34                                                                                                   
                      AM                                                                                                               

Roger,

Latest numbers from my tuneup of a Motorola 390A IF deck (tubes selected
for
best SNR at 150 microvolts input at 455kHz) and Collins 390A RF deck (6DC6
and 3 6C4 mixers chosen for best SNR):

IF deck SNR at 150 microvolts, 455kHz, URM25 fed directly into IF deck per
TM, 400Hz modulation at 30%
Bandwidth                            SNR
16kHz                                    27.8 dB SNR per TM method, 0dBm
with no modulation
8kHz                                        27.7 dB SNR
4kHz                                        30.5 dB SNR
2kHz                                        30.2 dB SNR

Hooking up the Collins RF deck to the above Motorola IF deck then yields:
 Test conditions - URM fed directly into RF deck (no 50-120 ohm matching
attenuator), 4 microvolts from the URM at 750 kHz, 400 Hz modulation at 30%
Bandwidth                            SNR
16kHz                                    23.7 dB SNR
8kHz                                        25.4 dB SNR
4kHz                                        27.4 dB SNR
2kHz                                        28.6 dB SNR

Also at 2kHz bandwidth and URM feeding the 390A directly (no 50-120
matching
attenuator), 400Hz modulation at 30%, I get about 0.35 microvolt for 10dB
SNR

Further, when I use the 50-120 ohm matching attenuator from the URM25 into
the 390A and 4 microvolt input, 750kHz carrier freq, 16kHz bandwidth,400 Hz
modulation at 30%, all per the -35 TM method, I get 14.9dB SNR.

I think I am about as "there" as I can get with my current set of tubes.
I'm a little disappointed that I can't get more than just over 30 dB SNR
from the IF deck.  However, I am getting a reasonable amount over 20 dB SNR
for the RF deck/IF deck combination at all IF bandwidths.

Is this time to quit the fussing and start listening to the receiver for
pleasure?

Very best,
Tom, W4PG