Trying to find out how to properly measure antenna SWR and Watt readings

prcguy

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The whips on these cheap mag mounts are thin piano wire and after 30 seconds of key down at 25w you will burn your finger touching the whip. The steel is lossy at VHF and there is too much RF current for the wire size so the whip cannot dissipate the heat generated over its length in that amount of time.

Or do you know of something else that would explain the heat?

"...I have some cheap 2m/70cm mag mount antennas with whips made from thin black coated steel wire and they get hot at 25 watts because steel is not a good conductor for antennas. "
I think you said the problem with that 'cheap' thingy. Steel will handle RF/power just fine. If it gets hot then look for another problem.
 

LostSignal

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"...I have some cheap 2m/70cm mag mount antennas with whips made from thin black coated steel wire and they get hot at 25 watts because steel is not a good conductor for antennas. "
I think you said the problem with that 'cheap' thingy. Steel will handle RF/power just fine. If it gets hot then look for another problem.
I don't remember saying "steel is not a good conductor for antennas..." because I didn't even know that to even say that??? :unsure: I think you're quoting someone else that said that and I remember that being said, I just don't remember who said it? I just know that I did not.

Anyways, "I" was wondering how they calculate how much an antenna can accept such and such amount of wattage... I did ask that particular question though.
 

LostSignal

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The whips on these cheap mag mounts are thin piano wire and after 30 seconds of key down at 25w you will burn your finger touching the whip. The steel is lossy at VHF and there is too much RF current for the wire size so the whip cannot dissipate the heat generated over its length in that amount of time.

Or do you know of something else that would explain the heat?
At my old job, I had some XTL's setup to transmit "test data", if you will, to the OC repeater systems for fire... long story short, the radios were not TX'ing even though I knew they worked? I go to move one of the mag mounts that I had and the only way to "slide" it off of the surface it was on and pretty much just about out of reach, I had to grab the bottom part of the base/antenna area as that was THEEE ONLY way due to how it was situated. I IMMEDIATELY had this burning sensation through the palm of my hand and it is very hard to describe it? I wouldn't actually classify it as a "burn", but I can tell you it felt as if it went straight to my bones as well??? Very hard to explain/describe how it felt, but I CAN tell you it hurt like a MrFr!!! It hurt in that same spot for about 2x weeks or thereabouts. Very painful I can tell you that...
 

prcguy

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That's kind of complicated as RF travels mostly on the skin of a conductor. The surface area rather than the cross section would be used to calculate how much RF current it would take and how hot it might get vs how much heat it will dissipate, etc.

For HF, 14ga wire easily handles 1500 watts and wire much smaller would also handle that power for a limited amount of time. If the wire gets too small it will just melt like a fuse, then arc and burn. I think if you hit something like 36ga magnet wire with 100w you would be getting close to the fuse mode.

Anyways, "I" was wondering how they calculate how much an antenna can accept such and such amount of wattage... I did ask that particular question though.
 

LostSignal

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Without going into detail, I'll just say this... a few years ago, I downloaded a free version of EZNEC and even have a book. I just currently can't find the book due to just about everything I own is in storage and the book helps quite a bit with examples and stuff. Very neat program, but the free version only lets you play with up to 11x elements, but it gives you an idea of how it works. I would like to get the full version as it would be interesting to simulate my current and future antenna builds.

I bring this up because it has "skin affect" from what I remember and different types of "metal elements" to use for your antenna, which basically takes what you are talking about as part of the parameters for whatever antenna you are designing.
 
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