"Stefan Wolfe" wrote in
:


"KE5MBX" wrote in message
ups.com...
Hi,
What's all this business I hear people talking about blasting
people's car stereos or killing cars altogether with high-power RF? I
run 2m, 10m, and 11m in my jeep and I'd like to sort out the fact
from the legend and find out what kind of power I can use without
risking damage to my jeep or cars around me. At what power level is
front-end overload to a nearby radio likely? At what power level is
damage likely, and to what componets?

I am currently using only 50 watts on a 5/8 wave (2m), 25w on a 1/4
wave (10m), legal 4w on a 1/4 wave (11m)

Thanks,
Nelson KE5MBX


I think over 100W you may have problems with HF and VHF. It can be a
problem.

One thing that works real well is to transmit near the x-ray radar
band where you have privileges. The traffic may slow down a bit as you
set off the radar detectors :-)

Yeah, and it REALLY lights up the detector detectors....


--
Dave Oldridge+
ICQ 1800667

It doesn't take much. Back in the early '90s a group of us were returning
from a hamfest and I was riding in the back seat of one guy's late '80s
Ford something or other (Crown Victoria, maybe?). I was using my HT to
talk to the other car on 2m and the driver noticed that his cruise control
was gaining speed and when I unkeyed it settled down. Once I figured out
it was my HT causing it, loads of fun ensued.

If something is sensitive to RF, it probably won't take much to cause it
to malfunction. The fact is that nobody does RF shielding or protection
for consumer electronics, so there is no set power limit below which a
device may not be affected.

- Nate

--

"The optimist proclaims that we live in the best of all possible worlds,
the pessimist fears this is true."

On Feb 12, 4:40 pm, Nate Bargmann
wrote:
It doesn't take much. Back in the early '90s a group of us were returning
from a hamfest and I was riding in the back seat of one guy's late '80s
Ford something or other (Crown Victoria, maybe?). I was using my HT to

If something is sensitive to RF, it probably won't take much to cause it
to malfunction. The fact is that nobody does RF shielding or protection
for consumer electronics, so there is no set power limit below which a
device may not be affected.


The increased prevalence of EMI/EMC problems means that modern cars
are MUCH better about this. Almost all new cars go through a fairly
rigorous test program for immunity from radiated fields. Nobody wants
to have the engine or braking control systems fail when the police car
next to them calls home on their VHF low band radio. There's rafts of
SAE specs for this, but I don't recall the field strengths. Several
hundred volts/m though, is what I think.

Aftermarket addons (stereos, nav systems, etc.) aren't nearly as good
on the account. Some automotive equipment is exempt from Part 15 (for
instance, the nifty OBD II readers are pretty good RFI emitters...)

"Nate Bargmann" wrote in message

If something is sensitive to RF, it probably won't take much to cause it
to malfunction.


True. One time I was testing VHF antennas at 5 watts output in a quiet
garage. I kept hearing a clicking noise every time I keyed up. I traced
it to an analog multimeter on my bench. I was pegging the poor meter from
about ten feet away.

I installed an Icom 2000 into my Commodore, a 92 VP sedan with a V6 engine,
and everytime I keyed the mike at full TX power the engine would stall,
whether at idle or on the road, very disconcerting!
I cured the problem by re-routing the coaxial cable away from the computer.
VK2KCE

"Nate Bargmann" wrote in message
et...
: It doesn't take much. Back in the early '90s a group of us were returning
: from a hamfest and I was riding in the back seat of one guy's late '80s
: Ford something or other (Crown Victoria, maybe?). I was using my HT to
: talk to the other car on 2m and the driver noticed that his cruise control
: was gaining speed and when I unkeyed it settled down. Once I figured out
: it was my HT causing it, loads of fun ensued.
:
: If something is sensitive to RF, it probably won't take much to cause it
: to malfunction. The fact is that nobody does RF shielding or protection
: for consumer electronics, so there is no set power limit below which a
: device may not be affected.
:
: - Nate
:
: --
:
: "The optimist proclaims that we live in the best of all possible worlds,
: the pessimist fears this is true."

On Feb 12, 3:18 pm, "KE5MBX" wrote:
Hi,
What's all this business I hear people talking about blasting people's
car stereos or killing cars altogether with high-power RF? I run 2m,
10m, and 11m in my jeep and I'd like to sort out the fact from the
legend and find out what kind of power I can use without risking
damage to my jeep or cars around me. At what power level is front-end
overload to a nearby radio likely? At what power level is damage
likely, and to what componets?

I am currently using only 50 watts on a 5/8 wave (2m), 25w on a 1/4
wave (10m), legal 4w on a 1/4 wave (11m)

Thanks,
Nelson KE5MBX


you might have more issues with RF exposure to you and safety,
particularly on the 2m band, depending on where the antenna is.

But, as far as killing your car radio (or one next to you) goes, you'd
have to look at the coupling from your antenna to the car radio's. 2m
is going to be the worst case because the victim receiver is close to
that frequency, so the coupling from your antenna to its is highest.
The easy case is the car in the next lane (because it's reasonably far
away.. more than a couple wavelengths), so you could do some sort of
rule of thumb free space path loss kind of calculation...Say you're 5m
away at 144MHz.

Loss = 32.44 + 20*log10(d in km) + 20*log10(f in MHz) = 32.44 -46+43
dB = about 30 dB loss. You're radiating 50 W, and let's assume your
antenna is 3dBi, so your EIRP is 100W or +50dBm. The victim is seeing
+20dBm (a tenth of a watt)... about 2 Volts into a 75 ohm load.
Assuming the victim radio has protection diodes across the input,
you're probably not going to kill it. Run a kilowatt and it's another
story...


As a practical matter, my 2m antenna is about 1 meter from the car
radio antenna, and when I transmit at 50W, the FM car radio blocks,
but recovers just fine. Likewise, transmitting at 100W on HF. Your
mileage may vary, etc.

Jim, W6RMK