Dittel radio squelch

On 10/5/2016 10:20 AM, Martin Gregorie wrote:

Short wave AM broadcasting, is still there, since its in the band that's
strongly reflected by the ionosphere, so has beyond the horizon range
Many government stations still use AM these band, e.g. Voice of America.

True enough.

The Marine VHF band (156-162.025 MHz) used for much the same purposes as
the Air Band, i.e. ship to shore, ship to ship, port operations...

I suspect these are likely to remain AM for a very long time since they
can work well on much narrower channels than FM and are certainly
unlikely to get more band allocation in the forseeable futu just look
at the way that mobile phones snarf up any frequencies they can get.


Actually, the Marine VHF channels use FM. Also, FM can be very narrow
band these days.

Vaughn

On Wed, 05 Oct 2016 17:01:46 -0400, Vaughn Simon wrote:

Actually, the Marine VHF channels use FM. Also, FM can be very narrow
band these days.

IIRC they were AM back in the mid 60s (I remember setting up a boat's
transceiver back then, based on a ZC1. This was a NZ Army radio of WW2
vintage and certainly AM modulation - it was commonly used as a base
station for units using the US Army's WS48 backpack sets (battery driven
AM).

When did the Marine band switch to FM and why?


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

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.

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.

Tom

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 :-)

Megacycles - what a blast from the past! It was '68 or '69 and I was a
ground radio repair tech in the USAF when they switched from cycles to
Hertz. How traumatic...

On 10/5/2016 7:05 PM, 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.

--
Dan, 5J

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 :-)

--
Dan, 5J

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.

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. This happened with the original avionic setup (Peschges VP-4E Nav), when I added a Colibri logger and with my current setup (LX8080 Simple, V5 vario, Powerflarm Core and FLarmview 57) so the rest of the equipment doesn't seem to be a factor.

The radio is pretty sensitive - I've been at 2,000ft. ASL (1,900ft. AGL) on a mountain ridge in Hope and have been able to hear transmissions from people in the circuit at Delta Airpark (both airports are assigned the same frequency) 70Km away!

I tried JJ's progressive start up of the avionics with the radio squelch turned off and was pleasantly surprised to find that the noise didn't increase noticeably as I turned on the other units.

On Thu, 06 Oct 2016 08:14:34 -0600, Dan Marotta wrote:

Megacycles - what a blast from the past! It was '68 or '69 and I was a
ground radio repair tech in the USAF when they switched from cycles to
Hertz. How traumatic...

On 10/5/2016 7:05 PM, 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.

It was a hugely wide-ranging renaming blitz, as it replaced many of the
old descriptive unit names by the name of a relevant, famous and deceased
scientist, e.g. the MKS unit of work, formerly the watt.second
(electrical) or newton.metre (mechanical) became the Joule and the unit
of frequency (the cycle per second became the Hertz.

I suppose it rationalised things by naming virtually *all* units of
measurement apart from distance, mass and time after people, but against
that it meant that it was now necessary to remember the dimensions of a
unit, i.e. that a Joule is a watt.second and that watts are amps times
volts in order to make calculations involving power, time and energy.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |