Dittel radio squelch

On 10/5/2016 7:16 AM, BruceGreeff wrote:
Many new smartphones are transmitting in the 850-900mhz range. (Some are
even lower in 450,older ones are 2100, 1900, 1700...)

If you look in the spectrum allocation - depending on where you are - it
may be close enough for cross talk I expect on an older receiver.

The cause of the noise is unlikely to be the phone's transmitter. It is
more likely the wide-spectrum noise generated by the phone's digital
innards.

Except for the moribund old AM broadcast band, the only common use of AM
(amplitude modulation, AKA "ancient modulation") radio that I can think
of is aviation radios. The main reason that AM has been so unpopular
for the last half-century or so is because it is very difficult to build
an AM receiver that is immune to static and noise.

On Wed, 05 Oct 2016 08:48:44 -0400, Vaughn Simon wrote:

On 10/5/2016 7:16 AM, BruceGreeff wrote:
Many new smartphones are transmitting in the 850-900mhz range. (Some
are even lower in 450,older ones are 2100, 1900, 1700...)

If you look in the spectrum allocation - depending on where you are -
it may be close enough for cross talk I expect on an older receiver.

The cause of the noise is unlikely to be the phone's transmitter. It is
more likely the wide-spectrum noise generated by the phone's digital
innards.

Except for the moribund old AM broadcast band, the only common use of AM
(amplitude modulation, AKA "ancient modulation") radio that I can think
of is aviation radios. The main reason that AM has been so unpopular
for the last half-century or so is because it is very difficult to build
an AM receiver that is immune to static and noise.

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.

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.


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

Ah... The old days of driving across the southern US and listing to WLS
890 AM Rock N' Roll out of Chicago. This only worked at night, of course...

Memories,
Dan



On 10/5/2016 8:20 AM, Martin Gregorie wrote:
On Wed, 05 Oct 2016 08:48:44 -0400, Vaughn Simon wrote:

On 10/5/2016 7:16 AM, BruceGreeff wrote:
Many new smartphones are transmitting in the 850-900mhz range. (Some
are even lower in 450,older ones are 2100, 1900, 1700...)

If you look in the spectrum allocation - depending on where you are -
it may be close enough for cross talk I expect on an older receiver.
The cause of the noise is unlikely to be the phone's transmitter. It is
more likely the wide-spectrum noise generated by the phone's digital
innards.

Except for the moribund old AM broadcast band, the only common use of AM
(amplitude modulation, AKA "ancient modulation") radio that I can think
of is aviation radios. The main reason that AM has been so unpopular
for the last half-century or so is because it is very difficult to build
an AM receiver that is immune to static and noise.
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.

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.



--
Dan, 5J

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

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 |