FM for the Eddystone EA12?
 

On 2/2/2015 6:44 AM, gareth wrote:
I wonder if there had been any articles published for taking the
100kHz IF output of the EA12 RX and creating an FM discriminator
for it, possibly a pulse-counting discriminator at such a low frequency?



I recall when I was in college, The teacher showed us an old movie
produced by the US-Army on FM radio, it eatured SLOPE detection of an FM
signal... I will not say more but you could tell who in the class had a
ham license and/or experience with FM radio right quick when that hit.
(All the students ROFL in case nobody here is old enough to recall Slope
Detection).

--
Home, is where I park it.

---
This email has been checked for viruses by Avast antivirus software.
http://www.avast.com

FM for the Eddystone EA12?
 

"John Davis" wrote in message
...
On 2/2/2015 6:44 AM, gareth wrote:

I recall when I was in college, The teacher showed us an old movie
produced by the US-Army on FM radio, it eatured SLOPE detection of an FM
signal... I will not say more but you could tell who in the class had a
ham license and/or experience with FM radio right quick when that hit.
(All the students ROFL in case nobody here is old enough to recall Slope
Detection).

I know about the slope detectiion and am 65.

I don't have any of the very old gear, but every so often I listen to the
hams around 3.85 MHz. that use the old military and AM gear. While I don't
think it is really legal (and don't really care) some of those AM
transmitters sound beter if I switch to FM on my Icom 746 pro. I think when
they were made they seem to put out about as much FM as AM.

FM for the Eddystone EA12?
 

On Thu, 5 Feb 2015, Ralph Mowery wrote:


"John Davis" wrote in message
...
On 2/2/2015 6:44 AM, gareth wrote:

I recall when I was in college, The teacher showed us an old movie
produced by the US-Army on FM radio, it eatured SLOPE detection of an FM
signal... I will not say more but you could tell who in the class had a
ham license and/or experience with FM radio right quick when that hit.
(All the students ROFL in case nobody here is old enough to recall Slope
Detection).

I know about the slope detectiion and am 65.

I think it might be more the younger crowd. There was that period, in the
late forties or early fifties were very narrow FM was promoted, no need
for the big modulation transformer, and no being detected by input stages
to audio amplifiers. But slope detection was the usual mode, since
virtually no shortwave receivers had FM detectors. Except one could get
an external FM adapter for a late model HRO (I think, there was an
accessory socket for that, but I'm not sure if there was an FM detector;
people used the socket to add an external product detector).

And then of course, when 2m FM took off, lots of people converted their
existing AM rigs to FM by modulating the oscillator in some way, and using
slope detection for reception. Or there was a project in QST in the
summer of 1971, add a converter to an AM broadcast portable, and use slope
detection, then the next month add an FM IF strip.

I used to use my SP-600 with a converter to listen to 2M FM circa 1972,
and I had to use slope detection.

I don't have any of the very old gear, but every so often I listen to the
hams around 3.85 MHz. that use the old military and AM gear. While I don't
think it is really legal (and don't really care) some of those AM
transmitters sound beter if I switch to FM on my Icom 746 pro. I think when
they were made they seem to put out about as much FM as AM.

That's weird. I thought those hardcore AMers wanted purity, and took
effort to ensure they were putting out a good signal. They sure aren't
using modulated oscillators, and I don't think anything where the
modulation would get back to the oscillator.

When I got my Hallicrafter's S-120A (that's the transistorized model)
shortwave receiver in 1971, that AM bunch was the only voice modulation I
could receive on the ham bands, since the receiver had way too weak a BFO.
(Only later did I learn enough to put a potentiometer between the antenna
and the receiver's antenna terminals to work as an attenuator, at which
point I could receive SSB, but only signals strong enough to overcome the
attentuation.). I gathered at the time that they were youngish, I'm not
sure why, maybe what they were talking about. And they probably are the
same bunch now, 44 years later. But at the time it was great, since I
could listen to hams talk.

Michael

FM for the Eddystone EA12?
 

"Michael Black" wrote in message
news:alpine.LNX.2.02.1502051950290.19867@darkstar. example.org...
On Thu, 5 Feb 2015, Ralph Mowery wrote:


I don't have any of the very old gear, but every so often I listen to the
hams around 3.85 MHz. that use the old military and AM gear. While I
don't
think it is really legal (and don't really care) some of those AM
transmitters sound beter if I switch to FM on my Icom 746 pro. I think
when
they were made they seem to put out about as much FM as AM.

That's weird. I thought those hardcore AMers wanted purity, and took
effort to ensure they were putting out a good signal. They sure aren't
using modulated oscillators, and I don't think anything where the
modulation would get back to the oscillator.


There may be two kinds of people using AM. One for 'good quality AM' ,but
the other is using mainly the military gear from around the WW2 era or so.
Maybe even before that if they can find it. That is the stuff that can
contain about as much FM as it does AM. The power supplies are often
feeding the oscillator as well as the final stages and not regulated very
well if at all. That probably helps modulate the transmitter to have a lot
of FM in the signal.

FM for the Eddystone EA12?
 

"Ralph Mowery" wrote in message
...
"Michael Black" wrote in message
news:alpine.LNX.2.02.1502051950290.19867@darkstar. example.org...
On Thu, 5 Feb 2015, Ralph Mowery wrote:
I don't have any of the very old gear, but every so often I listen to
the
hams around 3.85 MHz. that use the old military and AM gear. While I
don't think it is really legal (and don't really care) some of those AM
transmitters sound beter if I switch to FM on my Icom 746 pro. I think
when they were made they seem to put out about as much FM as AM.

That's weird. I thought those hardcore AMers wanted purity, and took
effort to ensure they were putting out a good signal. They sure aren't
using modulated oscillators, and I don't think anything where the
modulation would get back to the oscillator.

There may be two kinds of people using AM. One for 'good quality AM' ,but
the other is using mainly the military gear from around the WW2 era or so.
Maybe even before that if they can find it. That is the stuff that can
contain about as much FM as it does AM. The power supplies are often
feeding the oscillator as well as the final stages and not regulated very
well if at all. That probably helps modulate the transmitter to have a
lot of FM in the signal.

FM has always been a legal mode for 80m in the UK, it's just that nobody
normally uses it intentionally.
Provided you're using no more bandwidth than normal AM I can't see a
problem.
--
;-)
..
73 de Frank Turner-Smith G3VKI - mine's a pint.
..
http://turner-smith.co.uk

FM for the Eddystone EA12?
 

FM has always been a legal mode for 80m in the UK, it's just that nobody
normally uses it intentionally.
Provided you're using no more bandwidth than normal AM I can't see a
problem.

Well perhaps not 'always'. FM was not allowed prior to about 1952.

Jeff

FM for the Eddystone EA12?
 

In message , Jeff writes

FM has always been a legal mode for 80m in the UK, it's just that nobody
normally uses it intentionally.
Provided you're using no more bandwidth than normal AM I can't see a
problem.

Well perhaps not 'always'. FM was not allowed prior to about 1952.

In those days, some AM transmissions had quite a lot of FM on them!

10m FM works well using modified CB sets (2.5kHz deviation and 10kHz
channel spacing). It slope fairly well using my Eton SW receiver with
the AM filter switched to 'narrow'.
--
Ian

FM for the Eddystone EA12?
 

"Jeff" wrote in message ...
FM has always been a legal mode for 80m in the UK, it's just that nobody
normally uses it intentionally.
Provided you're using no more bandwidth than normal AM I can't see a
problem.

Well perhaps not 'always'. FM was not allowed prior to about 1952.

Jeff

When was FM first invented? BBC broadcast FM started in 1955.
--
;-)
..
73 de Frank Turner-Smith G3VKI - mine's a pint.
..
http://turner-smith.co.uk

FM for the Eddystone EA12?
 

On 06/02/2015 14:47, FranK Turner-Smith G3VKI wrote:
"Jeff" wrote in message ...
FM has always been a legal mode for 80m in the UK, it's just that nobody
normally uses it intentionally.
Provided you're using no more bandwidth than normal AM I can't see a
problem.

Well perhaps not 'always'. FM was not allowed prior to about 1952.

Jeff

When was FM first invented? BBC broadcast FM started in 1955.

http://en.wikipedia.org/wiki/Edwin_Howard_Armstrong

FM for the Eddystone EA12?
 

In message , FranK Turner-Smith G3VKI
writes
"Jeff" wrote in message ...
FM has always been a legal mode for 80m in the UK, it's just that nobody
normally uses it intentionally.
Provided you're using no more bandwidth than normal AM I can't see a
problem.
Well perhaps not 'always'. FM was not allowed prior to about 1952.
Jeff

When was FM first invented? BBC broadcast FM started in 1955.

The Murkins were trying it (for broadcast) in the early 40s (Google will
tell us).
--
Ian

FM for the Eddystone EA12?
 

In message , Jeefaw K. Effkay
writes
On 06/02/2015 14:47, FranK Turner-Smith G3VKI wrote:
"Jeff" wrote in message ...
FM has always been a legal mode for 80m in the UK, it's just that nobody
normally uses it intentionally.
Provided you're using no more bandwidth than normal AM I can't see a
problem.

Well perhaps not 'always'. FM was not allowed prior to about 1952.

Jeff

When was FM first invented? BBC broadcast FM started in 1955.

http://en.wikipedia.org/wiki/Edwin_Howard_Armstrong

I told you Google would tell us.
--
Ian

FM for the Eddystone EA12?
 

"FranK Turner-Smith G3VKI" wrote in message
...
FM has always been a legal mode for 80m in the UK, it's just that nobody
normally uses it intentionally.
Provided you're using no more bandwidth than normal AM I can't see a
problem.

I am sure every country has slightly differant rules. As I don't operate FM
below the 10 meter band I am not up on the current regulations in the US
where most of the stations I was hearing are at. At onetime in the US we
could use something like around 2 to 3 khz deviation on 80 meters I think .
That used to be called somethink like sliver band. Maybe still can.
However some of those on 3.85 MHz were way wider than that. I think that
below 30 MHz it is only on some portions of 10 meters that deviations as
wide as 5 KHz can be used in the US.

As I was saying above, I am not sure those AM / FM signals are legal in the
US, but don't really care. It is good that the hams have decided on a
frequency to meet and have fun with the old sets.

de KU4PT

FM for the Eddystone EA12?
 

On 06/02/15 12:39, Jeff wrote:

FM has always been a legal mode for 80m in the UK, it's just that nobody
normally uses it intentionally.
Provided you're using no more bandwidth than normal AM I can't see a
problem.

Well perhaps not 'always'. FM was not allowed prior to about 1952.

There was an adaptation of the WS19 (I think it was the WS32) that used
FM instead of AM, to test the use of FM on the battlefield. I guess it
was unsuccessful or other considerations mitigated against it, because
it wasn't adopted in that form, but some manpack sets and WS19 candidate
replacements were FM. I think that only about 100 WS32 were made.


--
Spike

"Hard cases, it has frequently been observed, are apt to introduce bad
law". Judge Rolfe

FM for the Eddystone EA12?
 

On Fri, 6 Feb 2015, FranK Turner-Smith G3VKI wrote:

"Ralph Mowery" wrote in message
...
"Michael Black" wrote in message
news:alpine.LNX.2.02.1502051950290.19867@darkstar. example.org...
On Thu, 5 Feb 2015, Ralph Mowery wrote:
I don't have any of the very old gear, but every so often I listen to the
hams around 3.85 MHz. that use the old military and AM gear. While I
don't think it is really legal (and don't really care) some of those AM
transmitters sound beter if I switch to FM on my Icom 746 pro. I think
when they were made they seem to put out about as much FM as AM.

That's weird. I thought those hardcore AMers wanted purity, and took
effort to ensure they were putting out a good signal. They sure aren't
using modulated oscillators, and I don't think anything where the
modulation would get back to the oscillator.

There may be two kinds of people using AM. One for 'good quality AM' ,but
the other is using mainly the military gear from around the WW2 era or so.
Maybe even before that if they can find it. That is the stuff that can
contain about as much FM as it does AM. The power supplies are often
feeding the oscillator as well as the final stages and not regulated very
well if at all. That probably helps modulate the transmitter to have a lot
of FM in the signal.

FM has always been a legal mode for 80m in the UK, it's just that nobody
normally uses it intentionally.
Provided you're using no more bandwidth than normal AM I can't see a problem.

But Ralph is complaining about a signal that is both AM and FM.

INtentional FM is different from incidental FM.

Certainly in the US (and I assume Canada), rules were in effect quite a
few decades ago about the stability of a signal. There was a point where
a signal had to be as stable as a crystal controlled signal on the HF
bands, which caused a shift to crystal control, I think that was even
before WWII. So incidental FM would seem to be out of the question after
that. It was only after WWII when things got crowded and better
techniques came along that VFOs made a comeback, obviously much better
built and stable than the variable oscillators of the old days. (And the
same sort of rule followed as the move up to higher frequencies.
Modulated oscillators would work the higher frequencies initially, then
the rule for better stability would come in, and the modulated oscillators
would move to the next higher band, and so forth).

If a signal is putting out both FM and AM, it is either doing it by
accident, and needs fixing, or is some weird form or modulation, that the
rules would either have a separate classification for, or a rule against
it.

Michael

FM for the Eddystone EA12?
 

On Fri, 6 Feb 2015, Ralph Mowery wrote:


"FranK Turner-Smith G3VKI" wrote in message
...
FM has always been a legal mode for 80m in the UK, it's just that nobody
normally uses it intentionally.
Provided you're using no more bandwidth than normal AM I can't see a
problem.

I am sure every country has slightly differant rules. As I don't operate FM
below the 10 meter band I am not up on the current regulations in the US
where most of the stations I was hearing are at. At onetime in the US we
could use something like around 2 to 3 khz deviation on 80 meters I think .
That used to be called somethink like sliver band. Maybe still can.
However some of those on 3.85 MHz were way wider than that. I think that
below 30 MHz it is only on some portions of 10 meters that deviations as
wide as 5 KHz can be used in the US.

There was definitely a period when FM was promoted for the HF bands, not
just 10Metres as later happened. Hallicrafters had an CW/FM HF
transmitter at one point, obviously it was a whole lot simpler to add FM
to a transmitter than AM. I thought SOnar also had some HF FM
transmitters in the same period, but looking around, I've yet to find what
I thought I'd read about that years ago.

Even later, the ARRL Handbook had a 220MHz transmitter into the seventies
that was primarily a CW transmitter (or exciter for a separate plate
modulated amplifier, but it also had narrow deviation FM, just in case
someone wanted to do phone up there. But the expectation was to use slope
detection, this wasn't part of the "move commercial 2way FM radios to the
ham bands for channelized operation", that came later.

Michael

FM for the Eddystone EA12?
 

"Michael Black" wrote in message
news:alpine.LNX.2.02.1502061353050.21109@darkstar. example.org...
But Ralph is complaining about a signal that is both AM and FM.

INtentional FM is different from incidental FM.

Certainly in the US (and I assume Canada), rules were in effect quite a
few decades ago about the stability of a signal. There was a point where
a signal had to be as stable as a crystal controlled signal on the HF
bands, which caused a shift to crystal control, I think that was even
before WWII. So incidental FM would seem to be out of the question after
that. It was only after WWII when things got crowded and better
techniques came along that VFOs made a comeback, obviously much better
built and stable than the variable oscillators of the old days. (And the
same sort of rule followed as the move up to higher frequencies. Modulated
oscillators would work the higher frequencies initially, then the rule for
better stability would come in, and the modulated oscillators would move
to the next higher band, and so forth).

If a signal is putting out both FM and AM, it is either doing it by
accident, and needs fixing, or is some weird form or modulation, that the
rules would either have a separate classification for, or a rule against
it.

I was not really complaining about the signal, just noting that it sounded
beter on FM than AM.

What might have been state of the art around 1930 or 1940 is probably not
legal now. Just as the old spark gap transmiters are not legal any more.
The station was suspose to be using AM, but probably the power supply was
not regulated enough that fed the audio amp and also the VFO so that the
changing of the VFO voltage was enough to FM the signal.

As you say Michael the design was for AM, but some of the old sets seem to
put out as much FM as they did AM. That was just the way it was 60 or 70
years ago. Especially some of the portable military gear.

Anyway I have no complaints about some guys having fun with the old gear as
long as they stay on or very near one frequency like they do.

FM for the Eddystone EA12?
 

"Spike" wrote in message
...
On 06/02/15 12:39, Jeff wrote:
FM has always been a legal mode for 80m in the UK, it's just that nobody
normally uses it intentionally.
Provided you're using no more bandwidth than normal AM I can't see a
problem.

Well perhaps not 'always'. FM was not allowed prior to about 1952.

There was an adaptation of the WS19 (I think it was the WS32) that used FM
instead of AM, to test the use of FM on the battlefield. I guess it was
unsuccessful or other considerations mitigated against it, because it
wasn't adopted in that form, but some manpack sets and WS19 candidate
replacements were FM. I think that only about 100 WS32 were made.

To ensure compatibility it would have been necessary to swap all the
military AM radios to FM at the same time.
The middle of a global war is not the time to make changes on that scale,
especially as the advantages of doing so seem minimal.
--
;-)
..
73 de Frank Turner-Smith G3VKI - mine's a pint.
..
http://turner-smith.co.uk

FM for the Eddystone EA12?
 

In message , FranK Turner-Smith G3VKI
writes
"Spike" wrote in message
...
On 06/02/15 12:39, Jeff wrote:
FM has always been a legal mode for 80m in the UK, it's just that nobody
normally uses it intentionally.
Provided you're using no more bandwidth than normal AM I can't see a
problem.

Well perhaps not 'always'. FM was not allowed prior to about 1952.

There was an adaptation of the WS19 (I think it was the WS32) that
used FM instead of AM, to test the use of FM on the battlefield. I
guess it was unsuccessful or other considerations mitigated against
it, because it wasn't adopted in that form, but some manpack sets and
WS19 candidate replacements were FM. I think that only about 100 WS32
were made.

To ensure compatibility it would have been necessary to swap all the
military AM radios to FM at the same time.

The middle of a global war is not the time to make changes on that
scale, especially as the advantages of doing so seem minimal.

Very true. Weren't there all sorts problems later on when some of our
emergency services got radio, and some areas used and AM, and some used
FM?

IIRC, most WW2 gear used simple 'Lo-Fi' forms of AM modulation (grid or
screen-grid), and not hi-level plate and screen (which requires more
valves, more current drain, a heavy mod transformer etc). As such, the
component count would be similar to FM equipment.

Also, AM detection is probably more tolerant of mistuning than FM.
There's also the reason why Air Traffic Control use AM and not FM - ie
lack of capture effect.


--
Ian

FM for the Eddystone EA12?
 

On 07/02/15 13:07, Ian Jackson wrote:
In message , FranK Turner-Smith G3VKI
writes
"Spike" wrote in message
...
On 06/02/15 12:39, Jeff wrote:
FM has always been a legal mode for 80m in the UK, it's just that
nobody
normally uses it intentionally.
Provided you're using no more bandwidth than normal AM I can't see a
problem.

Well perhaps not 'always'. FM was not allowed prior to about 1952.

There was an adaptation of the WS19 (I think it was the WS32) that
used FM instead of AM, to test the use of FM on the battlefield. I
guess it was unsuccessful or other considerations mitigated against
it, because it wasn't adopted in that form, but some manpack sets
and WS19 candidate replacements were FM. I think that only about 100
WS32 were made.

To ensure compatibility it would have been necessary to swap all the
military AM radios to FM at the same time.

The middle of a global war is not the time to make changes on that
scale, especially as the advantages of doing so seem minimal.

Very true. Weren't there all sorts problems later on when some of our
emergency services got radio, and some areas used and AM, and some used FM?


The various different services, Police, Ambulance, Fire, Coast Guard,
were on different frequencies so AM/FM was really of little consequence.

One of the, supposed, ideas behind 'Airwave' is that they can all be
linked but I am not sure how far this has actually been achieved, if at
all. Certainly the functionality that Kent Police were expecting is
still a pipe dream, based on some casual chats with end users who are
most unimpressed.


Compare that to some of the systems in place in the USA, where (even in
small towns) officers can access key information from a vehicle mounted
computer. (No, I've not been 'checked', I know someone who worked on the
systems.)

I have seriously wondered if the considerable delay in 'pushing' the
take up of the 'old' UHF emergency service frequencies wasn't, in part,
caused by concern that it may be necessary to 'rethink' the reliance on
Airwave. After all, I attended a presentation by OFCOM when it was still
not sure if it was the RA or OFCOM ;-) when they were, supposedly, about
to 'fill' the old frequencies with waiting users. Here we are, over a
decade on, and they are still 'talking'. Quite a feat, even for OFCOM ;-)


Also, AM detection is probably more tolerant of mistuning than FM.
There's also the reason why Air Traffic Control use AM and not FM - ie
lack of capture effect.


I suspect it is more historical Ian. Aircraft VHF sets are not VFO
controlled, these days there will be PLL but in the past they were
crystal controlled.

FM for the Eddystone EA12?
 

On 2/7/2015 8:07 AM, Ian Jackson wrote:
In message , FranK Turner-Smith G3VKI
writes
"Spike" wrote in message
...
On 06/02/15 12:39, Jeff wrote:
FM has always been a legal mode for 80m in the UK, it's just that
nobody
normally uses it intentionally.
Provided you're using no more bandwidth than normal AM I can't see a
problem.

Well perhaps not 'always'. FM was not allowed prior to about 1952.

There was an adaptation of the WS19 (I think it was the WS32) that
used FM instead of AM, to test the use of FM on the battlefield. I
guess it was unsuccessful or other considerations mitigated against
it, because it wasn't adopted in that form, but some manpack sets
and WS19 candidate replacements were FM. I think that only about 100
WS32 were made.

To ensure compatibility it would have been necessary to swap all the
military AM radios to FM at the same time.

The middle of a global war is not the time to make changes on that
scale, especially as the advantages of doing so seem minimal.

Very true. Weren't there all sorts problems later on when some of our
emergency services got radio, and some areas used and AM, and some used FM?

IIRC, most WW2 gear used simple 'Lo-Fi' forms of AM modulation (grid or
screen-grid), and not hi-level plate and screen (which requires more
valves, more current drain, a heavy mod transformer etc). As such, the
component count would be similar to FM equipment.

Also, AM detection is probably more tolerant of mistuning than FM.
There's also the reason why Air Traffic Control use AM and not FM - ie
lack of capture effect.



Actually not. Aircraft worldwide were using AM radios before FM became
popular. To change would require every radio-equipped airplane in the
world, from Cessna 150's to Antonov An-225's, change at the same time,
as well as all land-based stations including ATC, Flight Service
Stations, Unicoms, and even handhelds on the tarmac.

Plus, with the 8.33Khz channel spacing, deviation would be limited to
about +/- about 3Khz. Even with the old 25Khz channel spacing (allowing
about +/- 10Khz deviation), there is no clear advantage to FM over AM.
Fidelity is not a concern for the aircraft band.

It isn't going to happen :) It's going to take least 13 years just to
get new NextGen navigation system installed in aircraft in the United
States.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

FM for the Eddystone EA12?
 

On 07/02/15 11:14, FranK Turner-Smith G3VKI wrote:
"Spike" wrote in message
...

There was an adaptation of the WS19 (I think it was the WS32) that
used FM instead of AM, to test the use of FM on the battlefield. I
guess it was unsuccessful or other considerations mitigated against
it, because it wasn't adopted in that form, but some manpack sets and
WS19 candidate replacements were FM. I think that only about 100 WS32
were made.

To ensure compatibility it would have been necessary to swap all the
military AM radios to FM at the same time.
The middle of a global war is not the time to make changes on that
scale, especially as the advantages of doing so seem minimal.

I'm not sure that would have been a problem. New units would equip and
train with the new equipment, and then be sent to the front, replacing
those with older gear who would be retrofitted during their rest and
refit time. Units operated tactically, individual tanks talking to each
other and back to their own HQ. Comms between HQs (Company to Battalion
to Division, etc) would have been a simpler affair as far less radio
sets were involved.

And! Don't forget even the 32 set included CW, Signaller/Gunners were
trained in the mode, so there was interoperability built into the
system. Also, the 32 set RT was was AM/FM selectable, and physically and
electrically compatible - a line-replaceable unit.


--
Spike

"Hard cases, it has frequently been observed, are apt to introduce bad
law". Judge Rolfe

FM for the Eddystone EA12?
 

Also, AM detection is probably more tolerant of mistuning than FM.
There's also the reason why Air Traffic Control use AM and not FM - ie
lack of capture effect.


I suspect it is more historical Ian. Aircraft VHF sets are not VFO
controlled, these days there will be PLL but in the past they were
crystal controlled.


It is not the mis-tuning that is the reason, it is the ability to hear 2
stations when they transmit simultaneously, at least under some
conditions. Also it makes it easier to have a ground station transmit on
the same channel simultaneously from several different locations with
offset frequencies, which would be more difficult with FM.

Jeff

FM for the Eddystone EA12?
 

Very true. Weren't there all sorts problems later on when some of our
emergency services got radio, and some areas used and AM, and some used FM?

Even in the areas where the police used FM they were required to have
one AM channel for compatibility (on VHF). Some of the later police
mobiles were capable of both AM or FM on a channel by channel basis.

Jeff

FM for the Eddystone EA12?
 

In message , Jeff writes

Very true. Weren't there all sorts problems later on when some of our
emergency services got radio, and some areas used and AM, and some used FM?

Even in the areas where the police used FM they were required to have
one AM channel for compatibility (on VHF). Some of the later police
mobiles were capable of both AM or FM on a channel by channel basis.

As they (don't) say, "Standardisation is next to godliness"!


--
Ian

FM for the Eddystone EA12?
 

It is not the mis-tuning that is the reason, it is the ability to hear 2
stations when they transmit simultaneously, at least under some
conditions.

very true .....

FM for the Eddystone EA12?
 

On 07/02/2015 17:24, Jeff wrote:

Even in the areas where the police used FM they were required to have
one AM channel for compatibility (on VHF). Some of the later police
mobiles were capable of both AM or FM on a channel by channel basis.

I did that with a Pye Cambridge AM10B in the early 80s.

145.800 AM using the original circuit, plus few simplex and R4 (GB3FF)
for FM using the Garex NBFM IF kit, with audio applied to the screen
grid of the oscillator for transmit.

I could've saved a lot of work if I'd bought a Pye Whitehall to start with.

FM for the Eddystone EA12?
 

On 07/02/15 17:20, Jeff wrote:

Also, AM detection is probably more tolerant of mistuning than FM.
There's also the reason why Air Traffic Control use AM and not FM - ie
lack of capture effect.


I suspect it is more historical Ian. Aircraft VHF sets are not VFO
controlled, these days there will be PLL but in the past they were
crystal controlled.


It is not the mis-tuning that is the reason, it is the ability to hear 2
stations when they transmit simultaneously, at least under some
conditions. Also it makes it easier to have a ground station transmit on
the same channel simultaneously from several different locations with
offset frequencies, which would be more difficult with FM.

The 'capture' effect of FM is rather limited with NBFM. While you may
not be able to understand if two transmissions are present (just as you
may not on AM) you can often tell if there are.

To really gain (or perhaps not in this application) from the capture
effect, you don't really what NBFM.

The capture effect was mentioned as one of the reasons for UK CB being
FM but it was rather a dubious one, certainly a 'make weight' in the
RA's argument.

FM for the Eddystone EA12?
 

On 07/02/15 17:24, Jeff wrote:

Very true. Weren't there all sorts problems later on when some of our
emergency services got radio, and some areas used and AM, and some
used FM?

Even in the areas where the police used FM they were required to have
one AM channel for compatibility (on VHF). Some of the later police
mobiles were capable of both AM or FM on a channel by channel basis.

Really? The only ex-emergency service radio I've seen with AM and FM was
the 'Whitehall' which, if memory serves, was a Low Band unit and useful
for 4m. I repaired on once, quite a beast, with a mass of cables to
connect the boot unit to the control box.

Later radios tended to be pretty standard PMR sets from the likes of
Storno.

The 'Met' police did have a mix of AM and FM radios at one time but they
were different units. I think the AM sets were around 150MHz. FM was
just above 2m and UHF (450 or 460 ish). I think the cars, especially
those on traffic, used AM. Certainly the personal radios were UHF FM. I
knew someone who worked in the Met comms side.

I recall a major fire locally in 1990 or so when the police and fire
couldn't talk to each other at all via radio. In the end, they had a
couple of RAYNET people relaying messages between them, one was with the
senior fire officer the other with the senior police officer. The police
didn't even have enough radios for all of their officers and relied on
RAYNET.

FM for the Eddystone EA12?
 

In message , Brian Reay writes
On 07/02/15 17:20, Jeff wrote:

Also, AM detection is probably more tolerant of mistuning than FM.
There's also the reason why Air Traffic Control use AM and not FM - ie
lack of capture effect.


I suspect it is more historical Ian. Aircraft VHF sets are not VFO
controlled, these days there will be PLL but in the past they were
crystal controlled.


It is not the mis-tuning that is the reason, it is the ability to hear 2
stations when they transmit simultaneously, at least under some
conditions. Also it makes it easier to have a ground station transmit on
the same channel simultaneously from several different locations with
offset frequencies, which would be more difficult with FM.

The 'capture' effect of FM is rather limited with NBFM. While you may
not be able to understand if two transmissions are present (just as you
may not on AM) you can often tell if there are.

To really gain (or perhaps not in this application) from the capture
effect, you don't really what NBFM.

The capture effect was mentioned as one of the reasons for UK CB being
FM but it was rather a dubious one, certainly a 'make weight' in the
RA's argument.

I thought that the RAs insistence on FM was that the constant signal
envelope level was less likely to interfere with 'things' (apart from a
click at start and end of a transmission).
--
Ian

FM for the Eddystone EA12?
 

On Sat, 7 Feb 2015, Ian Jackson wrote:

In message , Brian Reay writes
On 07/02/15 17:20, Jeff wrote:

Also, AM detection is probably more tolerant of mistuning than FM.
There's also the reason why Air Traffic Control use AM and not FM - ie
lack of capture effect.


I suspect it is more historical Ian. Aircraft VHF sets are not VFO
controlled, these days there will be PLL but in the past they were
crystal controlled.


It is not the mis-tuning that is the reason, it is the ability to hear 2
stations when they transmit simultaneously, at least under some
conditions. Also it makes it easier to have a ground station transmit on
the same channel simultaneously from several different locations with
offset frequencies, which would be more difficult with FM.

The 'capture' effect of FM is rather limited with NBFM. While you may not
be able to understand if two transmissions are present (just as you may not
on AM) you can often tell if there are.

To really gain (or perhaps not in this application) from the capture
effect, you don't really what NBFM.

The capture effect was mentioned as one of the reasons for UK CB being FM
but it was rather a dubious one, certainly a 'make weight' in the RA's
argument.

I thought that the RAs insistence on FM was that the constant signal envelope
level was less likely to interfere with 'things' (apart from a click at start
and end of a transmission).

As I mentioned earlier, that was certainly one reason narrow band FM was
suggested for the HF bands decades ago. AM would get rectified by first
stages in audio ampliers, and the neighbors would be able to identify the
voice. None of that with FM.

But I remember tuning CB here in Canada in the early seventies, nad much
of the time, at least in the summer, it was a mass of heterodynes. Come
to think of it, since that was with a shortwave receiver, I wonder what it
was like on a channelized CB receiver?

The capture effect has always been attributed to FM, but in reality, it's
the limiters that bring on the capture effect. You can't have limiters
with AM, since that would wipe out the modulation. But if an FM receiver
had no limiters, where does the capture effect come from? The limiter
makes sure that a relatively modest difference between signal levels means
one will be on top. That said, I can remember instances of hearing two FM
signals at the same time, presumably they were pretty much identical
signal strength at the receiver.

On the other hand, maybe CB sets where FM is used don't have good
limiters. I finally found an SSB CB set a year or two ago, and once I
found information about it, discovered that the IF filter is relatively
wide. I was expecting a nice narrow SSB filter (which is why I'd hoped
for years go fined one), but instead it was sort of mediocre bandwidth,
wide enough for AM, and "narrow enough" for SSB. So they saved on the
flter. The odd part is, a good audio filter will make sure the
transmitted signal is narrow (if the actual bandwidth of a voice isn't
good enough), the IF filter only needs to knock off the unwanted sideband.
And I suppose on receiver, the channelized nature of CB means a wider
filter doesn't matter, the next channel up is far enough away so a wider
filter won't let in interference.

Michael

FM for the Eddystone EA12?
 

Really? The only ex-emergency service radio I've seen with AM and FM was
the 'Whitehall' which, if memory serves, was a Low Band unit and useful
for 4m. I repaired on once, quite a beast, with a mass of cables to
connect the boot unit to the control box.

Later radios tended to be pretty standard PMR sets from the likes of
Storno.

Many forces used the Marconi R675 and the Burndept 544 series which were
am/fm, Cleartome also did some but I can't remember the numbers.

The 'Met' police did have a mix of AM and FM radios at one time but they
were different units. I think the AM sets were around 150MHz. FM was
just above 2m and UHF (450 or 460 ish). I think the cars, especially
those on traffic, used AM. Certainly the personal radios were UHF FM. I
knew someone who worked in the Met comms side.

The am/fm set up was VHF only, all UHF was fm. Some forces elected to go
with fm for there vhf scheme, but there was always one am channel
available so that 'visiting' force vehicles colud comminicate if they
were on am only.

I recall a major fire locally in 1990 or so when the police and fire
couldn't talk to each other at all via radio. In the end, they had a
couple of RAYNET people relaying messages between them, one was with the
senior fire officer the other with the senior police officer. The police
didn't even have enough radios for all of their officers and relied on
RAYNET.

Indeed there never was any compatibility between Police, Fire and
Ambulance main schemes. Fire was exclusively am on vhf and Ambulances,
as I recall, were fm. Every ambulance authority did have the ERC
(Emergency Reserve) Channel for compatibility with neighbouring areas.

Jeff

FM for the Eddystone EA12?
 

On 08/02/15 10:16, Jeff wrote:

Really? The only ex-emergency service radio I've seen with AM and FM was
the 'Whitehall' which, if memory serves, was a Low Band unit and useful
for 4m. I repaired on once, quite a beast, with a mass of cables to
connect the boot unit to the control box.

Later radios tended to be pretty standard PMR sets from the likes of
Storno.

Many forces used the Marconi R675 and the Burndept 544 series which were
am/fm, Cleartome also did some but I can't remember the numbers.


Clearly it was somewhat of a 'moving feast' from force to force. I
recall a Met officer bemoaning the passing of the Storno personal radio
with a cast chassis and 'slab' battery (the Storno 500 I think). It
seems it was a useful emergency truncheon, whereas the replacements were
too fragile. (Cue some nonsense from a foot rest.)



Indeed there never was any compatibility between Police, Fire and
Ambulance main schemes. Fire was exclusively am on vhf and Ambulances,
as I recall, were fm. Every ambulance authority did have the ERC
(Emergency Reserve) Channel for compatibility with neighbouring areas.

I seriously wonder if there is now. One of the many things Airwave
promised was an integrated system, allowing all the Emergency services
to communicate if required. While I've not had the opportunity to check
this, based on other areas where 'features' seem to be vapour ware, I
wouldn't like to bet my pension on it working. No doubt there is some
committee somewhere managing it all, which some jobs worth(s) who hide
issues to score points later.


Several times, I've chatted to police officers with 'interesting'
antennas on their cars. They have generally been more than willing to
give a demo of the equipment onboard and say what it can and can't do.
in one case, I had been the passenger in a vehicle involved in an
accident and, while we were waiting for the tow trucks, the officer was
showing me the system for tracking stolen cars. By chance, it fired up
with a stolen car while he was showing me it. The stolen car got caught
up in the traffic jam the accident had caused (it was on a country road)
and another police vehicle caught it in a matter of minutes. All rather
impressive. It is one of the few bits of kit I've heard good comments
on. Conversely, the Airwave sets seem to be considered a disaster. Many
of the promised functions don't work/haven't been implemented and
officers frequently revert to conventional mobilephones. One function I
recall being shocked wasn't working, the ability to contact an officer
anywhere in the country (or even county). Amateurs can do that with
D(eath)Star. All in all, it seems to be little more than a local radio
system and not a very good one.