Dittel radio squelch

On Thursday, October 6, 2016 at 8:41:04 PM UTC+3, wrote:
I've had a similar problem from time to time with my FSG-50, every now and then a burst of noise. Eventually I realized it was only happening in the circuit for runway 25 at my home base, at about 2/3 of the way on the downwind leg. It hasn't happened this year so all I can thin of is that there may have been some equipment at the storage and construction yard beneath the downwind that was putting out electromagnetic interference.

Sometime in 1990 or 1991 I noticed that when I was speaking on the phone in my new flat in Newlands, Wellington there would sometimes be a "bzzzt" audible every four or five seconds. It seemed to happen more on rainy days.

One day I was gazing out the window while on the phone (the clouds can't have been all that low, or the rain heavy) This is something like the view. I was in the brick house on the left.

https://goo.gl/maps/r5WKiyG2RRA2

I noticed the bzzzt was happening in synchronization with the rotation of the big FO primary radar on Hawkins Hill 13.6 km away!

It would be interesting to look at the emissions of your phone with a
spectrum analyzer. We're not talking just the telephone signal here,
there are so many other electronic gizmos inside that little box that
could be putting out spurious radiation.

On 10/6/2016 9:21 AM, Bruce Hoult wrote:
On Friday, October 7, 2016 at 3:27:45 AM UTC+13, Dan Marotta wrote:
Noise is, by nature, made up of a wide range of frequencies, some of
which are amplitude modulated and at the same frequency as the radio is
tuned to (think lightening buzz in your AM radio). All of the filters
in the world will not keep them out of your speaker. They must be
attacked at the source, i.e., that cheap DC to DC converter (like I just
removed from my glider).

My perfectly working Becker radio started breaking squelch on all
frequencies immediately after installing the converter and went back to
its well-behaved self after removing power from the converter.

If you have not installed something new, or moved some wires, or changed
anything electronic in your glider, try turning your mobile phone off.
Besides, you'll enjoy the isolation that comes with it.

Good flying!

Dan

On 10/6/2016 3:45 AM, Bruce Hoult wrote:
On Thursday, October 6, 2016 at 3:38:05 PM UTC+13, 2G wrote:
On Wednesday, October 5, 2016 at 6:05:22 PM UTC-7, Vaughn Simon wrote:
On 10/5/2016 6:26 PM, Martin Gregorie wrote:
IIRC they were AM back in the mid 60s
Yes, but they weren't VHF then. They were in the 2 megacycle band and
required huge antennas for best range. Straight out of high school, my
first full-time job was working on those monsters.
All of this discussion of interference by out-of-band transmitters is way off topic; our aircraft radios have very good tunable bandpass RF filters that only pass thru the very specific VHF band we are listening to and reject all other bands. Otherwise we would be hearing transmissions from all sorts of transmitters, including other aircraft radios transmitting on an adjacent frequency. The place where the interference can pass thru into the receiver are not the antenna leads: it is the power leads where the RF filtering is less robust.
You can put as aggressive a choke as you want on the power leads :-)
Sure, a nasty chopper DC converter isn't going to do your RF environment a lot of good.

That's a totally different thing from a mobile phone operating on a post-GSM standard.

--
Dan, 5J

On Saturday, October 8, 2016 at 3:46:07 AM UTC+13, Dan Marotta wrote:
It would be interesting to look at the emissions of your phone with a
spectrum analyzer. We're not talking just the telephone signal here,
there are so many other electronic gizmos inside that little box that
could be putting out spurious radiation.

I have one :-)

http://rf-explorer.com

With the 240-960 MHz and 15-2700 MHz modules.

I've found it very useful for everything from verifying transmit power on glider radios, to checking for unused WIFI channels, to ...