Some of you questioned my technical sanity when I suggested dumping some VHF
power into a 5 Watt resistor and seeing if it can handle the power.
My original quote:
> If anyone doubts me, take your two meter radio and a let's say a 5 Watt
> resistor and hook them up. Key up your radio (at full power) and let it go
> immediately. You won't damage the resistor nor even make it warm. And
> you'll likely have keyed into it for at least 250 to 500 mS which is much
> longer than Rich's 10s of mS.
Well, I decided to put my money where my mouth is. I took 2 of Rich's 100
Ohm 3 Watt resistors (6 Watt total dissipation), put them in parallel and
soldered them to a PL-259. I then hooked them up to the output of my 2
meter setup which consists of an FT-847 and a Mirage amp which puts out
about 160 Watts.
The resistors measured 52.1 Ohms before I applied power. After a short CW
dah at full power output (160 W), I measured the resistors again - 51.2 Ohms
- within the error of my power meter. Did a little longer dah again. The
resistors still measured 51.2 Ohms. Lastly, I did a 2 second keydown. The
resistors started turning a little brown, were quite warm, but were STILL at
51.2 Ohms.
I feel my point was proven.
So the question is:
Rich claims that suppressor resistor are damaged by a nearly instantaneous
output of VHF energy due to an "oscillation." This "oscillation" occurs so
fast that the panel meters on the PA don't have time to respond. This, as
W8JI said, is probably on the order of nano-seconds or even a few
milliseconds at MOST.
If these same resistors can handle 160 Watts of VHF energy for 2 seconds,
how much could they really handle in less than a thousandth of the time? I
doubt enough to be damaged as Rich claims.
For that matter, I've not thought this through, but how many RF cycles at
VHF could take place in a matter of a few milliseconds? I guess you'd need
to calculate the period, which is 1/F. At 144 MHz, this is 6.9
nano-seconds. So if our event is on the order of nanoseconds you could get
just a couple of RF cycles going which ain't gonna hurt anything. The point
is that a short event as Rich claims is what happens isn't going to stress
components beyond a breaking point especially when it is so short it doesn't
even show up on the meter movements.
At least that's the way I see it.
73,
Jon
KE9NA
-------------------------------------
Jon Ogden
KE9NA
Member: ARRL, AMSAT, DXCC, NRA
http://www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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