Dear fellow antenna lovers,
I have an extra 2m radio(IcomV-8000) in my living room. I use a
magnet-mount 5/8 wave
antenna on the radiator cover. I never had any problems reaching the
local club repeater about
15miles away. I only use it to keep "watch" over the repeater so to
speak,while downstairs
cooking,cleaning,etc. It always worked very well in that use.
Recently....NO MATTER where I position the mag. on the cover, I GET
a small signal that
"CAN'T" be squalched away !!! It's just white noise/static !!! IF I
move my handie-talike to around the same area(with-in 10-12 ft.) IT
ALSO reacts the same way !! WHAT COULD BE causing this PHENOM ???
I have changed the power supply.....nothing changes the problem. I
shut off the computor......the cable unit.....the T.V.,nothing seems to
STOP that
small signal,ONLY on 146.970mhz that it happens. ONLY that
signal...and on both 2m radios. Can't squalch it out....this is
driving me co-co !!! The antenna is right next to a picture
window....but that really doesn't matter 'cause it does it on the
Handie-talkie,same frequency,day or night. Can't figure this one
out.....any ideas what to do ??? please...


73's, Paladin

In article .com,
Paladin wrote:

Recently....NO MATTER where I position the mag. on the cover, I GET
a small signal that
"CAN'T" be squalched away !!! It's just white noise/static !!! IF I
move my handie-talike to around the same area(with-in 10-12 ft.) IT
ALSO reacts the same way !! WHAT COULD BE causing this PHENOM ???

I've seen 2-meter spectrum noise from:

- Cable-TV leakage - worst is around 145.250, apparently due to the
video carrier leakage on Cable Channel 18.

- Multiple spurs generated by a switching power-supply regulator in
a Netgear wireless access point / IP router. The spurs were
apparently being radiated directly from the PC board, out through
the case - the power supply lead was adequately choked but this
didn't stop direct radiation. Other models of router (including
one from the same manufacturer) did not exhibit the problem.

- Noise radiated from telephone lines which have DSL networking
service enabled. Although the DSL signal is supposed to fall
entirely within the HF range, I believe that it has significant
harmonics up into the VHF which are not filtered out by the DSL
modems.

- Harmonic noise generated by a defective oscillator in an Ethernet
hub. This one was a doozie - it drifted through the 2-meter band
as temperature changed, and it caused horrendous squelch-tail
buzzing on several repeaters miles away when it drifted through
their input frequencies. Apparently it was radiating out through
the owner's Ethernet cables, and also getting back into the
building wiring through the power cord.

A device doesn't have to be complex to cause VHF QRM! Although it
didn't actually cause QRM, I did find another source of possible
interference recently when I tested and repaired a little two-tone
audio oscillator another ham had given me. It was a simple
battery-powered two-transistor oscillator based on a 1970s article in
QST. Due to its design (two simple twin-T oscillators using 2N2222
transistors) it was prone to break into a parasitic oscillation at one
point in the audio curve... it was putting out a nice 1 kHz audio
sinewave, with a VHF parasitic around 20 dB lower in amplitude,
wandering around from 130 to 160 MHz. One ferrite bead on the base
lead of each of the two transistors completely cured the problem.

Other people have reported nasty-noisy signals from oscillations in
TV-antenna preamplifiers... these have caused interference to 2-meter
ham operators, aviation band, and even to GPS (see the page at
http://www.gpsworld.com/gpsworld/art...l.jsp?id=43404
for a summary).

Can't figure this one
out.....any ideas what to do ??? please...

Do the "turn off and unplug" bit again, but go even further. For
starters, try turning off the main breaker for your whole
house/apartment. This will be a very clear way of telling you whether
the noise source is internal or external.

If it's internal to your home, turn the breaker back on and then start
unplugging every single device in the house (no matter how apparently
harmless) one at a time until the QRM goes away.

If it's external, go hunting. Get yourself a 2-meter directional beam
antenna (or make one - Google for "tape measure Yagi") and start
DF'ing.

If you track it to a neighbor's house, introduce yourself politely and
explain the problem and try to enlist their cooperation in finding the
source of the emission.

See if you can find someone in your area who has an RF spectrum
analyzer good up to 150 MHz or so. It can be very instructive to look
at the whole 2-meter band, and see whether you're seeing a single
carrier, broadband noise, or multiple narrowband spurs. A spectrum
analyzer, hooked to a portable Yagi via a 20' coax, makes a *very*
nice "characterize and locate" tool.

When I helped my city's RACES EC locate the source of some nasty
2-meter RFI which was desquelching his radios and interfering with his
ability to receive simplex, it took about 10 minutes with an
analyzer-and-Yagi combination for me to be able to say "Well, it's
your next-door neighbor's condo, upstairs, in the back, polarized at
around 45 degrees from the vertical. and is multiple spurs at about
50 kHz separation."

The bad news is that on many 2-meter frequencies, there's so much hash
and garbage in urban areas that it's necessary in practice to turn on
a receiver's tone-squelch, and force the receiver to remain muted
until it hear's a repeaters output CTCSS tone. If your repeater
doesn't put tone on its output, then this won't work, alas.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

"Paladin" wrote in
oups.com:

Dear fellow antenna lovers,
I have an extra 2m radio(IcomV-8000) in my living room. I use a
magnet-mount 5/8 wave
antenna on the radiator cover. I never had any problems reaching the
local club repeater about
15miles away. I only use it to keep "watch" over the repeater so to
speak,while downstairs
cooking,cleaning,etc. It always worked very well in that use.
Recently....NO MATTER where I position the mag. on the cover, I GET
a small signal that
"CAN'T" be squalched away !!! It's just white noise/static !!! IF I
move my handie-talike to around the same area(with-in 10-12 ft.) IT
ALSO reacts the same way !! WHAT COULD BE causing this PHENOM ???
I have changed the power supply.....nothing changes the problem. I
shut off the computor......the cable unit.....the T.V.,nothing seems to
STOP that
small signal,ONLY on 146.970mhz that it happens. ONLY that
signal...and on both 2m radios. Can't squalch it out....this is
driving me co-co !!! The antenna is right next to a picture
window....but that really doesn't matter 'cause it does it on the
Handie-talkie,same frequency,day or night. Can't figure this one
out.....any ideas what to do ??? please...


73's, Paladin




You might see if you can get them to change the frequency of the repeater.

SC

Dave Platt wrote:

I've seen 2-meter spectrum noise from:
. . . .

I'll add GPS receivers to that list. I've seen some pretty big spurs on
2 meters from a couple of units I've owned. But it's not the sort of
thing that's usually on constantly in a residential area.

Roy Lewallen, W7EL

"Paladin" wrote in message
oups.com...
Dear fellow antenna lovers,
I have an extra 2m radio(IcomV-8000) in my living room. I use a
magnet-mount 5/8 wave
antenna on the radiator cover. I never had any problems reaching the
local club repeater about
15miles away. I only use it to keep "watch" over the repeater so to
speak,while downstairs
cooking,cleaning,etc. It always worked very well in that use.
Recently....NO MATTER where I position the mag. on the cover, I GET
a small signal that
"CAN'T" be squalched away !!! It's just white noise/static !!! IF I
move my handie-talike to around the same area(with-in 10-12 ft.) IT
ALSO reacts the same way !! WHAT COULD BE causing this PHENOM ???
I have changed the power supply.....nothing changes the problem. I
shut off the computor......the cable unit.....the T.V.,nothing seems to
STOP that
small signal,ONLY on 146.970mhz that it happens. ONLY that
signal...and on both 2m radios. Can't squalch it out....this is
driving me co-co !!! The antenna is right next to a picture
window....but that really doesn't matter 'cause it does it on the
Handie-talkie,same frequency,day or night. Can't figure this one
out.....any ideas what to do ??? please...


73's, Paladin


I have it a little bit here and (can't recall) it might be the one I chased
last year. I went out for a one-on-one T-hunt and ended up back home,
pointing at my own garage door opener. It's proably LO radiation.

I picked it up in multiple locations, which was a puzzle at first. But now
I know which houses have a Genie Garage Door Opener ;-)

Boy O' boy....it's good to get a little humor about this ! I HATE TO
"not" UNDERSTAND a problem like this. The New England Spectrum
Management Group has their problems more important than mine. After
all, I DO have a "proper",outside 2m beam set up
and on that antenna there are "no issues". I need to use a VFO on 2m's
to see how wide of a signal I'm recieving. Maybe my RF-
current meter or the MFJ analyzer can aid me on my "indoor fox hunt".

chow.....paladin

David............Thank you for your "leads". I will follow them,one by
one to understand "WHY" this is happening. OF ALL the frequencies, why
did it have to be "this one"???? Any other,I could live with it...no
problem. I should "shelf" this issue because
I do have more radio thinmgs to take care of; HF in the car for the
first time.....raising my 80m loop up another 15ft. from 25ft. high,
FIELD DAY right down the road....! These little issues really get
under a ham's skin ;-)

Need a little persistance here...Thanks for the input,
Paladin/ma.

On Wed, 10 May 2006 09:05:54 GMT, Dave Oldridge
wrote:

what the resistance per foot is of the shield on LMR400 at 3.75mhz?

Hi Dave,

With the aid of an Ohmmeter, you should be able to determine that
without need for theory or books. Unless, that is, you simply try to
determine it for one foot's length where the resistance is bound to be
so small as to be buried in the resolution of the meter's display.

If we were to simply assign a total resistance of 0.1 Ohm, then from
what follows you would find yourself in serious trouble. You should
be shooting for at least one tenth of that value IN TOTAL. The
practical reality of this is that your connections may have more
resistance than the bulk cable. Further, at this level of resistance,
you need to make four lead (Kelvin) measurements.

I made a 55-inch diameter loop out of the stuff,

More to the matter would be the radiation resistance of this in the
80M band where you use it. This sets up the necessity of knowing that
LMR's resistance (much less the TOTAL). The radiation resistance of
such a small loop runs 0.002 Ohms.

If you used the same size loop at 160M, that figures out to 112 µOhms.
However, you use something smaller, and thus that figure is following
down further, faster.

I may try something more ambitious in 3/4 inch soft-drawn copper pipe,
about 6 feet in diameter. That should get me another 3 or 4 db, I think.

Then you would find that radiation resistance now turns out to roughly
double the former values.

Still, these coax loops seem to be working amazingly well for something so
simple and relatively inexpensive.

This observation (not really explained by you as to what constitutes
"amazingly well") can be a product of two realities:
1. You don't actually need much power to communicate;
2. Tuning up has been leveraged by a lot of loss.

73's
Richard Clark, KB7QHC

LMR400 outer conductor should be a bit less than 10 milliohms per foot
at 4MHz.

Rule of thumb: for copper, assuming thickness at least a couple of
skin depths, RF resistance in ohms per thousand feet is about
sqrt(freq(MHz))/(diameter(inches)). Aluminum will run 25% more or so.
I've assumed the aluminum foil shield of the LMR400 is at least 3 mils
thick, and I've neglected the overbraid.

Cheers,
Tom

In article .com,
Paladin wrote:

David............Thank you for your "leads". I will follow them,one by
one to understand "WHY" this is happening. OF ALL the frequencies, why
did it have to be "this one"???? Any other,I could live with it...no
problem.

I suspect it's probably a derivative of Murphy's Law ;-)

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!