rustyrivet

My Feedback: (6)

I bought a used 72mhz FM JR700 RX here some months back in the classifieds. It looked in nice condition and I stored it away in a draw for 3 months. Well, I finally go to table test it this week (with the antenna still rolled up)and the servo chatters most of the time and at one point I lost control for a second or so with no signal as I moved the stick. I had no problem when I tested two other of my used receivers in PCM I bought recently. This used JR700 cost me $16 shipped with the crystal included..... so no great loss if I need to toss it. But, I was wondering if a problem can be caused by testing an FM 72mhz RX sitting on the table too close in proximty to the TX. (like about within 24" of each other). It seems I had heard this mentioned once before. (??)

Steve Percifield

My Feedback: (14)

Yes, It's referred to as "swamping". Not unusual with FM stuff and should stop as you move the transmitter away from the receiver. It will be especially prominent when the batteries are fully charged. But, I have never seen it with PCM receivers..

RCPAUL

My Feedback: (1)

I have not seen this with FM rigs since about the 60s! It was fairly common when FM first came out. I can wrap the receiver around any of my 72 transmitter antennas and operation is solid as a rock.

Rodney

The better receivers have AVC (automatic volume control sometimes labled as AGC -automatic gain control) designed into the unit. Some of the less expensive receivers may not have a good design for their AVC and can be swamped out if the signal is to strong. So yes, having the transmitter to close might be the cause.

rustyrivet

My Feedback: (6)

Thanks for the input. I think I'll let someone assist me and have them hold the radio at the other end of the room and see if it still does it. If it's OK, then I'll do my usual 50 yrd range test.

bhorton

My Feedback: (26)

If the receiver antenna is still rolled up that might cause the problem.

rustyrivet

My Feedback: (6)

I know the manufacturer says that during a field test it is NOT necessary to pull antenna out of the radio. This is the reason why with the rx and tx just a few feet apart I didn't bother to unwind the R700 receiver antenna. (And it wasn't necessary to unwind the antennas on my two new PCM receivers which worked fine) But perhaps the same is not true for the FM R700 rx, and I need to undwind the antenna for a valid test. (?? dunno....but I guess I can see if it makes the decided difference, ay)

TFF

Unwind the rx. The PCM is going to filter. The straight FM is going to read what it thinks the signal is. I dont think anyone has removed the TX antenna for range testing since Kraft was king.

teebox11

My Feedback: (33)

Um, a low rx battery will. Distance, except for extreme out of range distance, will not. Always load test the rx batt. and make sure your tx batt. is full. I use my old 72 to test servos. Have servo, rx and batt, and tx in my lap while I'm watching crash vids on youtube. Never had a chatter in over a hundred years. Yes, I am as old as dirt. just say'n……………..

stevekott

Yes! Very common. +1 Swamped Rx.

Steve Percifield

My Feedback: (14)

definitely unwind the antenna for a valid range check. The swamping is entirely different, common, and no big deal. Just move the tranny back , or point the antenna in a different direction. I have had it happen on many brands of FM systems. Including 2 weekends ago when I was test flying an airplane for a friend. The transmitter was lying on the bench next to the plane, I was getting some jitters which I ignored. My friend ask about it , I explained , pointed the transmitter antenna away from the plane, it quit. Every happy..