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

"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 :-)

Stefan Wolfe wrote:
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 :-)

A number of years ago (I forget exactly what year) a
ham friend of mine discovered that he could cause a
new Cadillac to stall simply by keying his transmitter
as the Cadillac was passing his camper. That design
problem was probably fixed rather quickly.
--
73, Cecil http://www.w5dxp.com

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, 5:50 pm, "Stefan Wolfe" wrote:
"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 :-)

Where the heck do you get a 3cm transmitter, though? ha.

Cecil Moore wrote in
et:

Stefan Wolfe wrote:
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 :-)

A number of years ago (I forget exactly what year) a
ham friend of mine discovered that he could cause a
new Cadillac to stall simply by keying his transmitter
as the Cadillac was passing his camper. That design
problem was probably fixed rather quickly.

Back in the '70s I was working on a project that saw me reading papers on
the effects of EMR on various things. Amongst the papers was one dealing
with the susceptibility of the electronic anti-skid technology introduced
on heavy transport vehicles to meet (then) newer more stingent braking
distances. The braking systems were susceptible to ingress of RF,
resulting in wheel lockups. You can imagine the results of a 22 wheeler
at highway speed when a chook alongside comes up with "Breaker, Breaker,
any taker?" and locks up most of the wheels on the transport. I read
other papers on rear wheel lockups in a certain brand of passenger
vehicle due to RF induced downshift of the (electronically controlled)
automatic transmission at highway speeds.

The EMC issue seems better understood by vehicle manufacturers today,
though you still hear of RF triggered airbag deployments from time to
time.

I won't go into the papers on effects on aircraft, some of you may fly
from time to time! A paper on propagation of EM waves through rectangular
slots in thin sheet metal looks innocuous enough until you realise that
it is talking about an aircraft window (in the days when almost all
aircraft had a metal skin).

Owen

Dear Owen: Well do I remember the onset of EMC awareness that came with
the early anti-skid systems. One horror case took place in Chicago with a
bus. One of the many short bridges in Chicago has metal decking and a bus
stop at the far end of the bridge. The bridge also is aligned with the
Sears tower (in downtown Chicago it is difficult not to be aligned with some
strong RF radiator - it is worse than a carrier). Bus starts onto the
bridge. Patrons stand to get off at the next stop. Breaks fail while on
bridge. Driver fully asserts the brakes. Bus arrives at the end of the
bridge and the brakes start to work. People go flying.

I was a witness of the (very early and crude) method used to test
systems. Not anymore! Today, whole cars are zapped from all directions,
all frequencies, and at huge amplitudes. A huge effort was made to find out
what sort of signals a car might encounter. I once rode in a van all the
way to Chicago glued to a SA to record strong signals. The worst that I saw
was a VOR signal (few hundred watts at ground level with a very good radial
screen and near the road) and a CB signal. Others in the project measured
at VOA and LORAN sites. An FM broadcast antenna was found to radiate a huge
signal onto a public street - see, you know that antenna design would be
worked into the discussion - in this case an incompetent, but not unusual,
antenna design.

At work, we have a big RF amplifier used to zap devices in order to find
out where they die. Had to get a waiver from FCC because, even though the
amp requires three-phase, it could be used on 27 MHz.

Critical equipment is much more EMC capable today.

73, Mac N8TT
--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Owen Duffy" wrote in message
...
Cecil Moore wrote in
et:

Stefan Wolfe wrote:
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 :-)

A number of years ago (I forget exactly what year) a
ham friend of mine discovered that he could cause a
new Cadillac to stall simply by keying his transmitter
as the Cadillac was passing his camper. That design
problem was probably fixed rather quickly.

Back in the '70s I was working on a project that saw me reading papers on
the effects of EMR on various things. Amongst the papers was one dealing
with the susceptibility of the electronic anti-skid technology introduced
on heavy transport vehicles to meet (then) newer more stingent braking
distances. The braking systems were susceptible to ingress of RF,
resulting in wheel lockups. You can imagine the results of a 22 wheeler
at highway speed when a chook alongside comes up with "Breaker, Breaker,
any taker?" and locks up most of the wheels on the transport. I read
other papers on rear wheel lockups in a certain brand of passenger
vehicle due to RF induced downshift of the (electronically controlled)
automatic transmission at highway speeds.

The EMC issue seems better understood by vehicle manufacturers today,
though you still hear of RF triggered airbag deployments from time to
time.

I won't go into the papers on effects on aircraft, some of you may fly
from time to time! A paper on propagation of EM waves through rectangular
slots in thin sheet metal looks innocuous enough until you realise that
it is talking about an aircraft window (in the days when almost all
aircraft had a metal skin).

Owen

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

On Feb 12, 5:15 pm, "KE5MBX" wrote:
On Feb 12, 5:50 pm, "Stefan Wolfe" wrote:



"KE5MBX" wrote in message

oups.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 :-)

Where the heck do you get a 3cm transmitter, though? ha.

10.525 GHz is an amateur band, and is the same band used by the X-band
radars, and transmitters are readily available for $100. Gunnplexers
are one example, but people also use modified "microwave door openers"
to experiment in X band.

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...)