The AM Forum

...HEY...I NEED SOME INPUT,AS TO A REALLY GOOD RECEIVER...I'VE READ JOHNNY NOVICE'S GUIDE TO RECEIVERS,AND I WOULD LIKE SOME INPUT...
...HERE'S THE DEAL...A BUNCH OF US OPERATE AM ON 3725,AND ALL IS OK FINE WITH MY NC300,BUT WHEN A LOCAL HAM COMES ON,UP THE BAND,HE COMPLETELY WIPES OUT THE GUYS I'M IN QSO WITH...LAST NIGHT,THE GUYS I WAS IN QSO WID,WERE ABT40/9....BUT WHEN THIS HAM CLOSE BY COMES ON,ABT 15KC UP,ON LSB,MY RECEIVER JUST HEARS NOTHING,EXCEPT HIS SPLATTER...SOMETIMES I CAN DEAL WID IT,BY NARROWING THE IF,PHASING,ETC,BUT ALOT OF TIMES,I GOTTA SHUT DOWN...
...SOOOO....WHAT ARE YOUR IDEAS FER A BETTER RECEIVER,TO REDUCE THE SPLATTER,ETC...BTW,I'M ABT 3/4 MILE FROM THIS OTHER HAM....
....TNX...TIM....SK...

Cubic R3150
Racal RA6830
Harris RF590
Cubic R3030
Here are a few

R390A.

Sounds a bit deliberate, the neighbor's operating practices.
What's he running for a receiver against you ?

Try turning the RF gain down when it happens.   I have the same trouble with a PMR-7, problem goes away by backing off the RF just a little.   I listen to the 3725 group.   Wish we had a wider phone band for AM, but I bet you guys are glad we don't.

Hi Tim,

Well, first of all, 15kc away is plenty far for ssb. Normally, he should be down at least 50db 5kc away from his center freq. But if the guy is real close in distance to you, maybe he is simply so loud that even 70db down is enough to still cause you problems.  I have a ham that is one mile away. On 75M ssb I can hear him 15kc away. But this is simple overload and I live with it. Thankfully he is inactive except for corntests... ;D

The thing to do is to run some tests. Put in some receiver attenuation, like maybe 40db, or just connect a small wire to the back of your receiver. Tune him in at S9 and meaure how wide he is. Then put the antenna back on and measure some ssb other stations that are far from you and compare the bandwidths.  If he has a spaltter problem, you will see right away. If he is just too close and overloading you, this will be EZ to see too.

Either way, (if his signal is clean) when cornditions get crowded at night and signals are loud, there is little you can do with a broad receiver. I always have TWO receivers going all the time. One is hi-fi broad for AM and the other is my FT-1000D ricebox. With the ricebox I can often copy Calif AM stations on 75M through local ssb. It makes all the difference in the whirl when you need it.

So, looks like you are doing the right thing by looking for a hot receiver. The list supplied by Frank/GFZ will solve all your QRM problems.

73,
T

HMMMMM...I (WE) WUD LIKE U GUYS TO JOIN US...NO PROBLEM THERE...WELL,I DO TRY TURNING THE RF GAIN DOWN,ALONG WID IF,PHASING,ETC,PLUS DIFFERENT ANTENNAS...NO GO....THIS GUY IS RUNNING A COMMANDER AMP,WHICH I FEEL HE DOESNT NEED,AS HE IS IN QSO WID GUYS ABT 100-200 MILES AWAY...HIS RIG IS SOME KIND OF YAESU,I THINK A 1000,OR WHATEVER...I DO HAVE ANOTHER RIG TO TRY AS A RECEIVER,BEING A KENWOOD TS950SD,BUT I LIKE THE IDEA OF A BA RECEIVER..I WUD HAVE TO LOOK INTO MUTING THE '950,WITH T/R ETC,BUT THIS MITE BE MY LAST RESORT...I DONT WANNA ZAP THE KENWOOD....BTW,I USE THE '950 FER CW,NOT FONE OF ANY KIND...NICE RCVR,BUT STILL NOT SURE OF USING IT,WITH THE OLD GEAR,MAINLY BECAUSE OF T/R....TIM....SK..

You're worried about burning up the RX front end when T/Ring the TX to RX, right?

The way I handle this problem is fail safe. What I do it key the antenna relay FIRST and the contacts from the antenna relay mute the receiver and disconnect the antenna - first. Then another separate relay gets keyed by this antenna relay and in turn turns on/off the TX and rest of the station.

The point is that there is no way the TX can come on without the receiver being muted and the antenna disconnected. Plus there is a mechanical delay of the contacts of the cascaded relays that eliminates any pops from audio, etc.

Before I did this, I popped the front end of a receiver. I agree it is dangerous to depend on a single T/R relay using multiple receivers and a high power transmitter.

73,
T

Which knob is that switch on Tim, the RF or AF gain.  Seems as if it is on the Audio Gain.  Turn it all the way counter clock wise and the 1st RF amp is tied  to all the rest of the tubes for gain.  Turn it clockwise and it runs wide open.  I don't remember which but have you tried both positions?

If the 1st RF is running wide open all the time it is saturating and moving RF gain just a bit won't help much.  The manual tell you.  In one position you can reduce the 1st RF stage as you vary the rest.