On Sat, 11 Dec 2004 22:23:47 -0500, "Dave VanHorn"
wrote:

|
| So, in all honesty, YOU can't really say how dangerous operation of an FM
| receiver will be; but you KNOW that it's potentially harmful.
|
|Given that the aircraft voice comms are just above the FM BCB, and the
|typical first IF is 10.7 MHz, it's not too hard to imagine the LO sitting
|right on the tower comm frequency.
|You may only radiate a microwatt, but you're much closer to that antenna on
|the aircraft than the tower is. Inverse square law makes it very easy for
|you to win that contest.

Correct. Let me offer a slightly different but illustrative example.

Since this is cross-posted to some non-ham groups, bear with me. In
the 1960's I operated my amateur station on the two-meter (144 MHz)
band using several hundred watts of AM and directional antennas.

I'm in Tucson where we have both a commercial airport and D-M AFB. An
acquaintance of mine, also a ham, was the FAA tower chief at Tucson
International.

One day he calls me on the phone and says that the tower guys at D-M,
knowing he was a ham, called him first rather than the FCC, to report
that I was interfering with their tower communications.

To make an involved detective story short, it turned out that another
ham, who lived just outside the AFB was using a Heathkit "Twoer". The
Twoer used a super-regenerative receiver and was picking up my signal
and re-radiating it on the tower frequencies. I was getting blamed
for the other guy's illegal transmissions.

Considering that this technology is probably used in more receivers
today than any other type (garage door openers, computer wireless
links, etc.) if I'm flying, I hope they are all turned off.

|
|This is a pointless argument though. It's a health and safety issue, and
|you either follow the airline's rules, or I hope they boot you off the plane
|(optionally, landing first for your convenience) It is just that simple.
|

Our club repeater also ended up interfering with the local tower.

It seems that the transmitter PLL was unstable, and "hopping" between that
frequency, and ours.
We were clearly audible in their recordings.

Lest any "experts" step in and claim that you can't receive FM on an AM
receiver, I'd ask them to consider what effect the passband filter of the AM
receiver's IF might have on the FM signal as it deviates from side to
side....

I hit the magic codes and took the repeater down, once we determined that
this was indeed the source.

A re-tweak of the transmit PLL, and a stub filter cut to pass 146.730 and
reject the tower frequency, cured the problem, and insured that if it ever
happens again, they probably won't hear us. The tower now has our phone
numbers in their books, in case there is ever another problem. The tower
complimented our rapid and assertive handling of the problem in their
closing letter to the FCC.

Repeater cans don't do much for signals that are far out of band.

Our club repeater also ended up interfering with the local tower.

It seems that the transmitter PLL was unstable, and "hopping" between that
frequency, and ours.
We were clearly audible in their recordings.

Ouch. That'd be categorized as a "double-plus ungood" for certain!

Lest any "experts" step in and claim that you can't receive FM on an AM
receiver, I'd ask them to consider what effect the passband filter of the AM
receiver's IF might have on the FM signal as it deviates from side to
side....

I believe the magic words are "slope detection". The resulting audio
on the AM receiver isn't great (it's often distorted) but it's
certainly there.

I hit the magic codes and took the repeater down, once we determined that
this was indeed the source.

A re-tweak of the transmit PLL, and a stub filter cut to pass 146.730 and
reject the tower frequency, cured the problem, and insured that if it ever
happens again, they probably won't hear us. The tower now has our phone
numbers in their books, in case there is ever another problem. The tower
complimented our rapid and assertive handling of the problem in their
closing letter to the FCC.

Well done!

--
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!

Years ago I was flying in a friends private plane. I used a Ht on 146.52 to
make some contacts. My friend announces that we are lost. It took about 10
minutes before I found a landmark and got him following a road to the airport.
My friend believes that the HT interfered with his radio compass and put use
off course. After the HT was turned off and time was allowed, the compass
returned to normal. I don't know how it happened, but it did! Now I just
carry my ht on the plane and do not operate!

Randy ka4nma

On 13 Dec 2004 02:41:45 GMT, ospam
(Theplanters95) wrote:

|Years ago I was flying in a friends private plane. I used a Ht on 146.52 to
|make some contacts. My friend announces that we are lost. It took about 10
|minutes before I found a landmark and got him following a road to the airport.
|My friend believes that the HT interfered with his radio compass and put use
|off course. After the HT was turned off and time was allowed, the compass
|returned to normal. I don't know how it happened, but it did! Now I just
|carry my ht on the plane and do not operate!

Despite my concerns expressed earlier I will confess to contacting a
couple of my buddies using my 2-meter handi from an aircraft, with the
pilot's permission.

'Course, he was also a ham and we were flying in a sailplane that had
a couple of light bulbs for electronics. [g] The only way to fly.

'Course, he was also a ham and we were flying in a sailplane that had
a couple of light bulbs for electronics. [g] The only way to fly.

Well, if one of the light bulbs goes out, they'll blame it on the nearest
ham

Seems pretty safe, but I still wouldn't do it without permission.

I'm like that when I drive.
I'm in the left seat, it's my car and my ass, and I make the decisions.
I have actually had a passenger throw a fit because I wouldn't make a left
turn that I wasn't convinced was safe, in the 1-2 seconds I had to look at
it when the passenger hollered "turn left here". He got to walk home.