Equipment damage from high power rx ?

[Cabover Bob]

Please forgive my ignorance here, but I heard 25+ years ago that one radio can be damaged by another higher powered radio if both are in tx mode simultaneously. Kinda forgot about it until this video from a local regarding the SF Bay Area Friday night roll call.

Hopefully someone can explain in layman's terms......



73
Todd

 

[999]

It for the same reason that a high SWR can damage your radio, but from a different cause.
High SWR is power reflected back into the radio from a poorly tuned antenna, where someone sitting close to someone else while transmitting with high power is just slamming the output side of the radio with a lot of power from an outside source.
Same effect for different reasons.

 

[KneeBiter]

Back in the 80s I was in my car talking on the radio AM and while I was talking a buddy with a huge ceramic tube amp in his Suburban pulled up beside me which I didn't realize until I smelled the magic smoke coming from my radio. I looked over to a man with the laughter of a child. I was not happy. Finals were toast.

 

[groundwire]

If thats the case, than how come all these super high power shoot out guys aren't killing all their radios keying up right next to each other? None

 

[999]

If thats the case, than how come all these super high power shoot out guys aren't killing all their radios keying up right next to each other? None

Near same power levels. It's like 2 4 watt radios keying next to each other.
Think of it like two streams or two raging rivers flowing towards each other. So long as the current is about equal they won't back up along one or the other, but if you have a river flow directly into a stream, that stream will overflow it's banks really quick and go boom.

 

[999]

If thats the case, than how come all these super high power shoot out guys aren't killing all their radios keying up right next to each other? None

I've seen this happen a couple times with a cheap radio and an amp as small as a 667. The other radio was killed by a sweet sixteen, but I don't remember what the radio was though.

 

[nomadradio]

Receiver damage is more likely if you get too close to a high-power RF source.

Had a group of OTR drivers who liked their HR2510 radios back in the day. The power switch on the radio only removed power from the low-power parts of the radio, receiver and switching circuits. The final and driver stages are always "hot" so long as the power cord is connected to 13.8 Volts DC. The drive voltage to the base terminal of each one turns it on. Or keeps it turned off.

Turned out that leaving the final transistor "plugged in" to its source of DC power is safe until the RF energy coming down the coax from the antenna reaches a voltage threshold that turns on the final transistor's base terminal. Of course the radio's low-level circuits are all still turned off, so the final becomes a RF oscillator. Now it provides its own drive current to the base circuit after the nearby radio unkeys.

It continues to oscillate at some random RF frequency until it overheats and smokes numerous components in the RF final circuits.

Some drivers would find only a smoke-filled cab and blown fuse on the radio. The lucky few would hear a screech from the speaker, and see a pegged meter. Pulling the power cord would sometimes rescue that radio before it could go critical and melt down.

Oh, and never, ever leave your FT-101 radio connected to an antenna while the radio is unattended. Had a customer who couldn't understand why his FT101's MOSFET antenna-amplifier transistor kept blowing out. Until one day the channel 6 operator who drove by that time of day keyed up close enough to bleed the TV and stereo. Harry's idiot light came on, and he went to the basement to check his baby FT101. Sure enough, the receiver had gone deaf again. After getting it fixed this time he decided to unhook the antenna from the radio when it wasn't in use. Didn't have this problem again.

73