[Boatanchors] Questions on 51J4 as Ham receiver

[Al Klase]

Hi Gene,

Eugene Hertz wrote:

>Hello all,
>
>I am starting to play with using my 51J4 as my station receiver.  Had a few questions...
>
>1. The meter on the J4 is calibrated in DB (why not dbm?). 
>
dB indicates a /relative/ signal level.  In this case decibels above the 
AGC threshold.  That's had to define but the threshold is a few 
microvolts.  dBm indicates an /absolute/ signal level referenced to 1 
milliwatt.

>So how would I give a signal report in terms of "S" or db over S?
>  
>
To make things easy, call 30db S9.  That's going to be in the 50-100 uV 
range that's pretty standard.

>2. Seemingly counter intuitive, when I reduce the RF gain, the meter shows larger DB. When the RF gain is all the way down (off), I see the max reading on the meter. This is counter intuitive because generally (with gain all the way up) weak signals produce low db readings and strong signals produce large db readings. Why increase the db readings with lower rf gain?
>  
>
The S=meter reads gain control voltage, either AVC or MVC.  This is a 
good feature with AVC off you can judge signal strength by how far the 
meter comes upscale as you turn down the RF Gain,

>3. Tuning: When I am listening to CW, I can change the beat note either by adjusting the VFO or the BFO.  As a listener I would not normally care.  But now I want to zero beat my transmitter (central electronics 100V) so that it is transmitting on the frequency I am listening to.  Problem is, depending on the BFO dial position in the J4, my transmitter could be +/- hundreds of hertz (possibly 1k? I haven't measured).  If I want to transmit on the same frequency the other operator is on, what is the best method to adjust the BFO so when I zero beat I am on his frequency?
>  
>
You want the BFO frequency, when the knob is set to the mark, to be at  
the center of the IF passband.  Let the radio warm up thoroughly with 
the BFO on.  Turn on the CALIBRATOR.  Tune to a cal signal, they're 
stronger on the broadcast band.  Set the filter selector to 1KC and the 
SELECTIVITY (xtal filter) to 4.  Tune for max S-meter reading. You guys 
without product detectors may want to turn off the BFO when taking meter 
readings.  Set the BFO knob on the mark and adjust T-106 (inside) for 
zero beat.

Now, turn off the crystal filter, SELECTIVITY = 0, and turn the filter 
selector to 3KC.  Turn the main tuning knob until the S-meter shows 
you're 20db down the filter skirt.  Zero beat with the BFO knob and mark 
that position with a sliver of adhesive lable on the knob skirt.  Repeat 
for the other side of the filter.  These marks will be appropriate 
settings for USB and LSB. 

Good luck,
Al

Al Klase - N3FRQ
Flemington, NJ
http://www.skywaves.ar88.net/