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[kristianjohnsen]

It's generally thought to be good practise to never run a transmitter without an antenna.

Sometimes this happens inadvertently in "our world".  Has anyone encountered gear-damaging situations?

[jasonfinnigan]

No, it should not damage them. The only difference it could possible make is there would be no ohm load on it, that's kinda like asking if a power amp would be damaged from being turned on with no speaker plugged in.

[Jason Glass]

No, it should not damage them. The only difference it could possible make is there would be no ohm load on it, that's kinda like asking if a power amp would be damaged from being turned on with no speaker plugged in.

No, It's not like that at all at RF frequencies.  A zero ohm load (or also an infinite load) reflects all of the transmitter's power back into the last component inside the amp.  If the amp output has an isolator or circulator with sufficient dummy load (which many high-end systems do, internally), it may survive.  If it does not have the isolator, the reflected power is dissipated as heat.  If this heat exceeds the dissipation specs of that component, the amp fries.

I have seen a 90's era Clair IEM combiner fail after mere seconds of transmitting without a load.

I have also seen a Shure PA821 operate just like new after running for hours without an antenna attached.

It's best practice to always have a load attached to an RF amp of any kind.

[Lyle Williams]

Agreed that best practice is to have a load attached.

Anything built on a commercial scale should be designed to be safe working into an open or short circuit.  Too many warranty claims if end-users can break things easily!

[kristianjohnsen]

No, it should not damage them. The only difference it could possible make is there would be no ohm load on it, that's kinda like asking if a power amp would be damaged from being turned on with no speaker plugged in.

I kinda feel like you were trying to belittle my question, all while putting your foot in your mouth while replying.  Quite satisfying, to be honest

[kristianjohnsen]

It's best practice to always have a load attached to an RF amp of any kind.

This is what I was taught as well. 

The two scenarios I sometimes encounter where the rule is broken:  IEM transmmitters that are transported with the antennas detatched may be plugged in before someone thinks to attach the antenna.  Or mic beltpacks where the user somehow manages to unscrew the antenna.

I have never had any damage, but it's good to know that old wisdom still holds true.

PS:  I know what you look like now, came accross a very good Shure-video on Youtube the other day

[kristianjohnsen]

Agreed that best practice is to have a load attached.

Anything built on a commercial scale should be designed to be safe working into an open or short circuit.  Too many warranty claims if end-users can break things easily!

I seem to remember a time not so long ago when even power amps didn't like running with either a short or open circuit :-/

[Jason Glass]

This is what I was taught as well. 

The two scenarios I sometimes encounter where the rule is broken:  IEM transmmitters that are transported with the antennas detatched may be plugged in before someone thinks to attach the antenna.  Or mic beltpacks where the user somehow manages to unscrew the antenna.

I have never had any damage, but it's good to know that old wisdom still holds true.

PS:  I know what you look like now, came accross a very good Shure-video on Youtube the other day

There is usually little danger with belt pack transmitters.  This is partly because lower-end gear outputs low power and the components can handle it, while high-end stuff usually has some variation of isolator to minimize intermod products when multiple packs are operated in close proximity.

Now that you know what I look like, I hope you'll introduce yourself if you see me at a gig.  I haven't been to Norway in a few years, but who knows what the future holds?   

[jasonfinnigan]

No, It's not like that at all at RF frequencies.  A zero ohm load (or also an infinite load) reflects all of the transmitter's power back into the last component inside the amp.  If the amp output has an isolator or circulator with sufficient dummy load (which many high-end systems do, internally), it may survive.  If it does not have the isolator, the reflected power is dissipated as heat.  If this heat exceeds the dissipation specs of that component, the amp fries.

I have seen a 90's era Clair IEM combiner fail after mere seconds of transmitting without a load.

I have also seen a Shure PA821 operate just like new after running for hours without an antenna attached.

It's best practice to always have a load attached to an RF amp of any kind.

This may have used to have been the case but most devices anymore have a built-in protection circuits, that goes for wireless stuff for sound, and other RF devices, like high power Wifi, Radios (HAM, emergency etc) and celluar. Years ago they did not but I have not seen any that did not anymore.

[jasonfinnigan]

I seem to remember a time not so long ago when even power amps didn't like running with either a short or open circuit :-/

Running without a load is only an open circuit not a short. They still don't like shorts, most don't even like a 2omh load.

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