Thanks for the helpful replies about the car radio that would only get
a couple AM stations. The guy ignored my advice about trimming the
antenna, and just bought another antenna, even though the one he had
had worked fine with the previous radio.

The new radio worked fine with the new antenna. Did he just get
lucky?

Thanks.

On Sat, 28 Nov 2009 23:47:31 -0500, mm wrote:

Thanks for the helpful replies about the car radio that would only get
a couple AM stations. The guy ignored my advice about trimming the
antenna, and just bought another antenna, even though the one he had
had worked fine with the previous radio.

The new radio worked fine with the new antenna. Did he just get
lucky?

No. He ignored your idiotic advice and replaced a defective antenna.

Did you propose he trim and replace metal every time he changes channels?

AZ Nomad wrote:

On Sat, 28 Nov 2009 23:47:31 -0500, mm wrote:

Thanks for the helpful replies about the car radio that would only get
a couple AM stations. The guy ignored my advice about trimming the
antenna, and just bought another antenna, even though the one he had
had worked fine with the previous radio.

The new radio worked fine with the new antenna. Did he just get
lucky?

No. He ignored your idiotic advice and replaced a defective antenna.

Did you propose he trim and replace metal every time he changes channels?


'Trimming the antenna' means to adjust a variable capacitor to
compensate for the capacitance of the coaxial cable. It affects the gain
on the upper end of the AM band, since the antenna is used as a voltage
probe, rather than a typical antenna design. It was standard procedure
whenever a car radio was installed or repaired to 'trim' it as the last
step of the job. Most US car radios allowed the adjustment by removing
the tuning knob and using a small screwdriver to adjust the capacitor. A
lot of cheap imported radios had no adjustment, and had very poor AM BCB
performance.

It has absolutely nothing to do with cutting metal.


--
The movie 'Deliverance' isn't a documentary!

"Michael A. Terrell" wrote in message
m...

AZ Nomad wrote:

On Sat, 28 Nov 2009 23:47:31 -0500, mm wrote:

Thanks for the helpful replies about the car radio that would only get
a couple AM stations. The guy ignored my advice about trimming the
antenna, and just bought another antenna, even though the one he had
had worked fine with the previous radio.

The new radio worked fine with the new antenna. Did he just get
lucky?

No. He ignored your idiotic advice and replaced a defective antenna.

Did you propose he trim and replace metal every time he changes channels?


'Trimming the antenna' means to adjust a variable capacitor to
compensate for the capacitance of the coaxial cable. It affects the gain
on the upper end of the AM band, since the antenna is used as a voltage
probe, rather than a typical antenna design. It was standard procedure
whenever a car radio was installed or repaired to 'trim' it as the last
step of the job. Most US car radios allowed the adjustment by removing
the tuning knob and using a small screwdriver to adjust the capacitor. A
lot of cheap imported radios had no adjustment, and had very poor AM BCB
performance.

It has absolutely nothing to do with cutting metal.


___________________________
You forgot to mention that with age, the antenna coaxial cable would get
water in it, and
reception would suffer. Adjusting the trimmer would make little or no
difference in this situation. Replacement was the only fix.

On Sun, 29 Nov 2009 01:23:58 -0600, "Klaatu"
wrote:


"Michael A. Terrell" wrote in message
om...

AZ Nomad wrote:

On Sat, 28 Nov 2009 23:47:31 -0500, mm wrote:

Thanks for the helpful replies about the car radio that would only get
a couple AM stations. The guy ignored my advice about trimming the
antenna, and just bought another antenna, even though the one he had
had worked fine with the previous radio.

The new radio worked fine with the new antenna. Did he just get
lucky?

No. He ignored your idiotic advice and replaced a defective antenna.

Did you propose he trim and replace metal every time he changes channels?


'Trimming the antenna' means to adjust a variable capacitor to
compensate for the capacitance of the coaxial cable. It affects the gain
on the upper end of the AM band, since the antenna is used as a voltage
probe, rather than a typical antenna design. It was standard procedure
whenever a car radio was installed or repaired to 'trim' it as the last
step of the job. Most US car radios allowed the adjustment by removing
the tuning knob and using a small screwdriver to adjust the capacitor. A
lot of cheap imported radios had no adjustment, and had very poor AM BCB
performance.

It has absolutely nothing to do with cutting metal.


___________________________
You forgot to mention that with age, the antenna coaxial cable would get
water in it, and
reception would suffer. Adjusting the trimmer would make little or no
difference in this situation. Replacement was the only fix.

But it worked fine and got lots of AM stations with the previous
radio. (He only changed the radio because he wanted something
fancier.)

In article ,
Michael A. Terrell wrote:
Most US car radios allowed the adjustment by removing
the tuning knob and using a small screwdriver to adjust the capacitor. A
lot of cheap imported radios had no adjustment, and had very poor AM BCB
performance.

My V expensive Blaupunkt doesn't have an aerial trimmer - nor have I seen
one for many a year. Thought most had some form of automatic matching
circuit these days?

--
*To err is human. To forgive is against company policy.

Dave Plowman London SW
To e-mail, change noise into sound.

Klaatu wrote:

You forgot to mention that with age, the antenna coaxial cable would get
water in it, and reception would suffer. Adjusting the trimmer would
make little or no difference in this situation. Replacement was the
only fix.


There would be little or no reception by that point, and replacing
the antenna was a common repair for me in the '60s & '70s. We kept a
used car radio antenna in the service department to test a radio in the
car. Unplug the car's antenna and plug in the test antenna. if you
picked up some stations, the antenna was bad & had to be replaced. At
that time we could get most OEM antennas delivered in two days or under.


--
The movie 'Deliverance' isn't a documentary!

"Dave Plowman (News)" wrote:

In article ,
Michael A. Terrell wrote:
Most US car radios allowed the adjustment by removing
the tuning knob and using a small screwdriver to adjust the capacitor. A
lot of cheap imported radios had no adjustment, and had very poor AM BCB
performance.

My V expensive Blaupunkt doesn't have an aerial trimmer - nor have I seen
one for many a year. Thought most had some form of automatic matching
circuit these days?


Fancy words for a little more stage gain and lower performance. They
did that because most people were too stupid to adjust the trimmer
properly, and would return new radios as defective. Newer car radios
are crap when compared to the earlier designs, if you want to listen to
a weak AM station.

--
The movie 'Deliverance' isn't a documentary!

On Sun, 29 Nov 2009 09:48:43 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
Michael A. Terrell wrote:
Most US car radios allowed the adjustment by removing
the tuning knob and using a small screwdriver to adjust the capacitor. A
lot of cheap imported radios had no adjustment, and had very poor AM BCB
performance.

My V expensive Blaupunkt doesn't have an aerial trimmer - nor have I seen
one for many a year. Thought most had some form of automatic matching
circuit these days?

Well that's related to my point. Maybe there is an automatic
matching circuit in the new radio that's not working, and he just got
lucky that it matched the new antenna. ??

So if he ever takes this radio to another car, again the AM won't work
if the matching circit doesn't work and he's not lucky with the new
car's antenna.


I asked him to read the manual to find out about antenna trimming, but
he didn't reply about that.

In article ,
Michael A. Terrell wrote:

"Dave Plowman (News)" wrote:

In article ,
Michael A. Terrell wrote:
Most US car radios allowed the adjustment by removing the tuning
knob and using a small screwdriver to adjust the capacitor. A lot of
cheap imported radios had no adjustment, and had very poor AM BCB
performance.

My V expensive Blaupunkt doesn't have an aerial trimmer - nor have I
seen one for many a year. Thought most had some form of automatic
matching circuit these days?


Fancy words for a little more stage gain and lower performance. They
did that because most people were too stupid to adjust the trimmer
properly, and would return new radios as defective. Newer car radios
are crap when compared to the earlier designs, if you want to listen to
a weak AM station.

It might be the case that US buyers are too stupid to know what a trimmer
was or how to adjust it - but don't think this applied to the rest of the
world. Especially considering the facilities on a decent aftermarket radio
these days - the handbook on mine is the size of the Bible. Nor can I say
I've noticed AM performance being worse since trimmers disappeared. Unless
you include those infernal screen aerials. The last radio I had with a
trimmer dated from the early '70s.

--
*Hard work pays off in the future. Laziness pays off now *

Dave Plowman London SW
To e-mail, change noise into sound.

In message , "Dave Plowman (News)"
writes
In article ,
Michael A. Terrell wrote:
Most US car radios allowed the adjustment by removing
the tuning knob and using a small screwdriver to adjust the capacitor. A
lot of cheap imported radios had no adjustment, and had very poor AM BCB
performance.

My V expensive Blaupunkt doesn't have an aerial trimmer - nor have I seen
one for many a year. Thought most had some form of automatic matching
circuit these days?

In my 'shack', I've got a Philips RD525LEN LW/MW/FM car radio (bought
recently for one GBP, from a stall at a charity sale). The aerial is 5
foot of wire in the attic, with maybe 15 feet of 75 ohm TV coax (braid
connected to the attic water tank) down to the radio.

The coax is much longer than it would be in a car, and it's also the
'wrong sort of coax' (capacitance per unit length will be higher).
Nevertheless, it works very well, with no lack of 'liveliness' at the HF
end of the medium wave (where you normally expect to set the aerial
trimmer, peaking up a weak signal at (typically) 1500kHz.

I've got the instruction/installation manual, but there's absolutely no
reference to any aerial trimmer. There might be some form of 'automatic
matching circuit' but, if there is, what does it consist of? You would
need a varicap diode, driven from the AGC line, and some form of servo
loop which would automatically adjust and optimise the diode
capacitance. It all seems a bit complicated - bearing in mind that a
simple aerial trimmer capacitor has been satisfactory for some 60 or 70
years. I just can't see it myself.
--
Ian

On Sun, 29 Nov 2009 13:43:11 -0500, "Michael A. Terrell"
wrote:

Klaatu wrote:

You forgot to mention that with age, the antenna coaxial cable would get
water in it, and reception would suffer. Adjusting the trimmer would
make little or no difference in this situation. Replacement was the
only fix.

There would be little or no reception by that point, and replacing
the antenna was a common repair for me in the '60s & '70s. We kept a
used car radio antenna in the service department to test a radio in the
car. Unplug the car's antenna and plug in the test antenna. if you
picked up some stations, the antenna was bad & had to be replaced. At
that time we could get most OEM antennas delivered in two days or under.

That was also in the days when the coax cable was attached to the
antenna base with a weird connector. I found far more coax cables to
be defective than antennas. The cable used was some kind of very low
capacitance coax, with a very tiny center conductor floating inside a
plastic tube. The center wire would often break from the vehicle
vibration. I couldn't find any details on the coax type.

These daze, the antenna is built into the windshield or side window of
the vehicle.

Looking at the data sheet of a modern AM/FM front end chip, the AM
section appears to be Hi-Z input:
http://www.atmel.com/dyn/resources/prod_documents/doc4913.pdf
See Page 5.
ATR4251 provides an AM buffer amplifier with low input
capacitance (less than 2.5 pF) and low output impedance (5ohms).
The low input capacitance of the amplifier reduces the capacitive
load at the antenna, and the low impedance output driver is able
to drive the capacitive load of the cable. The voltage gain of the
amplifier is close to 1 (0 dB), but the insertion gain that is
achieved when the buffer amplifier is inserted between antenna
output and cable may be much higher (35 dB). The actual value
depends, of course, on antenna and cable impedance.

No mention of any AM trimmer capacitor tuning. My guess(tm) is that
older AM front ends were looking at a tuned circuit, instead of a
broadband amplifier. The tuned circuit was looking at some specific
capacitance in order to be on frequency. The trimmer compensated for
the variations in cable and antenna capacitance in order to resonate
this tuned circuit.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:

On Sun, 29 Nov 2009 13:43:11 -0500, "Michael A. Terrell"
wrote:

Klaatu wrote:

You forgot to mention that with age, the antenna coaxial cable would get
water in it, and reception would suffer. Adjusting the trimmer would
make little or no difference in this situation. Replacement was the
only fix.

There would be little or no reception by that point, and replacing
the antenna was a common repair for me in the '60s & '70s. We kept a
used car radio antenna in the service department to test a radio in the
car. Unplug the car's antenna and plug in the test antenna. if you
picked up some stations, the antenna was bad & had to be replaced. At
that time we could get most OEM antennas delivered in two days or under.

That was also in the days when the coax cable was attached to the
antenna base with a weird connector. I found far more coax cables to
be defective than antennas. The cable used was some kind of very low
capacitance coax, with a very tiny center conductor floating inside a
plastic tube. The center wire would often break from the vehicle
vibration. I couldn't find any details on the coax type.


RG/62, 93 ohm coax. The same as what IBM used for their early
computer networks. This, according to the Delco engineers that taught
their annual automotive electronics seminars. I drove them crazy with
design questions, and was surprised that so many bad ideas came from
marketing fools, and the UAW.


These daze, the antenna is built into the windshield or side window of
the vehicle.


Some are, but my current vehicle has a real whip antenna


Looking at the data sheet of a modern AM/FM front end chip, the AM
section appears to be Hi-Z input:
http://www.atmel.com/dyn/resources/prod_documents/doc4913.pdf
See Page 5.
ATR4251 provides an AM buffer amplifier with low input
capacitance (less than 2.5 pF) and low output impedance (5ohms).
The low input capacitance of the amplifier reduces the capacitive
load at the antenna, and the low impedance output driver is able
to drive the capacitive load of the cable. The voltage gain of the
amplifier is close to 1 (0 dB), but the insertion gain that is
achieved when the buffer amplifier is inserted between antenna
output and cable may be much higher (35 dB). The actual value
depends, of course, on antenna and cable impedance.

No mention of any AM trimmer capacitor tuning. My guess(tm) is that
older AM front ends were looking at a tuned circuit, instead of a
broadband amplifier. The tuned circuit was looking at some specific
capacitance in order to be on frequency. The trimmer compensated for
the variations in cable and antenna capacitance in order to resonate
this tuned circuit.


Exactly! use an extra stage to hide a problem, rather than deal with
it properly.

You know that a broadband, untuned input circuit has lower gain and
more noise that a tuned circuit designed to pass little more than a
couple channels at a time. The older, tuned input design reduced the
design by at least one gain stage, along with the extra tracking
problems. Better designs used moving slug tuners with three or four
coils. Lets remember that most people don't give a damn about listening
to AM radio anymore, and certainly not on long drives. They might
listen to the local news, or a ball game, but everything else is FM, Cd
or MP3.

The best Am receivers I've owned were a solid stated ARN-6 DRF, and a
couple frequency selective voltmeters with a tuned antenna and preamp.


You've talked about designing two way radios, and I've worked with
telemetry designs on multiple bands, along with C-band & Ku band sat TV
equipment. No one in their right mind would use an untuned antenna
system and expect good performance. The noise floor, intermod and
co-channel interference would be horrible.


--
The movie 'Deliverance' isn't a documentary!

On Sun, 29 Nov 2009 19:08:16 -0500, "Michael A. Terrell"
wrote:

Looking at the data sheet of a modern AM/FM front end chip, the AM
section appears to be Hi-Z input:
http://www.atmel.com/dyn/resources/prod_documents/doc4913.pdf

Exactly! use an extra stage to hide a problem, rather than deal with
it properly.

I beg to differ somewhat. The problem with anything below about 7 MHz
is that atmospheric noise far exceeds the field strength of any
possible weak signal worth receiving. It makes no sense to have an
ultra-low-noise receiver front end on a lower frequency receiver.

However, note that this chip was also made for receiving short wave
DRM and HD Radio, which can be up to 30MHz. The level of complexity
necessary to build a tracking filter, with automagical impedance
matching is a bit much for consumer electronics. The result of using
a simple amplifier is lousy image rejection, overload problems,
sub-harmonic problems, intermod problems, and lousy NF which has an
effect on 7 Mhz reception.

An untuned amplified front end for impedance matching might seem like
an inferior solution, but it's certainly the cheapest, which drives
the consumer car radio market.

You know that a broadband, untuned input circuit has lower gain and
more noise that a tuned circuit designed to pass little more than a
couple channels at a time.

Current or voltage gain? In this case, it's current gain, which seems
quite high (35dB). It's prime purpose is to transform the rather high
antenna impedance down to something the chip can digest (50 ohms???).
Certainly an untuned front end has a worse NF than one that is tuned
and matched. However, the atmospheric noise at BCB frequencies will
swamp out any alleged improvement produced by the better sensitivity.

The older, tuned input design reduced the
design by at least one gain stage, along with the extra tracking
problems. Better designs used moving slug tuners with three or four
coils.

These daze, the slug tuners would cost more than the extra stages.
Transistors are one of the cheapest parts in the radio.

Lets remember that most people don't give a damn about listening
to AM radio anymore, and certainly not on long drives. They might
listen to the local news, or a ball game, but everything else is FM, Cd
or MP3.

See Ibiquity, DRM and HD Radio:
http://en.wikipedia.org/wiki/Digital_Radio_Mondiale
http://en.wikipedia.org/wiki/HD_Radio
http://www.ibiquity.com/hd_radio
BCB and SW stereo is kinda strange, but does work in strong signal
areas.

The best Am receivers I've owned were a solid stated ARN-6 DRF, and a
couple frequency selective voltmeters with a tuned antenna and preamp.

http://jproc.ca/rrp/rrp3/argus_arn6.html
My guess(tm) is that the reason they're "better" is not because of
improved sensitivity, but because of improved overload handling or
dynamic range. Much of the garbage and trashy sound is nothing more
than overload or intermod from strong nearby stations.

You've talked about designing two way radios, and I've worked with
telemetry designs on multiple bands, along with C-band & Ku band sat TV
equipment. No one in their right mind would use an untuned antenna
system and expect good performance. The noise floor, intermod and
co-channel interference would be horrible.

True. I suppose someone could conjure an proper BCB receiver. Most
of the better ham radio HF transceivers would certainly quality, such
as Elecraft K3:
http://www.w1vd.com/ElecraftK3.html
Well, maybe not. AM is certainly low on the priority list. Still,
the test numbers are far better than the typical AM/FM receiver.

However, even if the receiver were superior, the real problem is
hiding in the antenna system. One big improvement for BCB only would
be to install a big fat loading coil at the base of the antenna. It
wouldn't improve the received signal strength, but it would provide a
lower impedance to the coax and receiver front end, eliminating the
front end impedance matching stage.

The bottom line is always cost. The next incremental improvement in
performance is going to require substantial hardware in the receiver
front end. It's not a trivial change and will be expensive. I don't
think that Joe Sixpack will pay the price.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sun, 29 Nov 2009 19:08:16 -0500, "Michael A. Terrell"
wrote:

Lets remember that most people don't give a damn about listening
to AM radio anymore,

It's certainly heartwarming to think that conservatives aren't most
people, but even 10% of the market is usually enough to get some
attention by manufacturers.

In NY and Philly are AM stations I would listen to. Not sure about
the rest of the country.


and certainly not on long drives. They might
listen to the local news, or a ball game, but everything else is FM, Cd
or MP3.

In article ,
Ian Jackson wrote:
My V expensive Blaupunkt doesn't have an aerial trimmer - nor have I seen
one for many a year. Thought most had some form of automatic matching
circuit these days?

In my 'shack', I've got a Philips RD525LEN LW/MW/FM car radio (bought
recently for one GBP, from a stall at a charity sale). The aerial is 5
foot of wire in the attic, with maybe 15 feet of 75 ohm TV coax (braid
connected to the attic water tank) down to the radio.

The coax is much longer than it would be in a car, and it's also the
'wrong sort of coax' (capacitance per unit length will be higher).
Nevertheless, it works very well, with no lack of 'liveliness' at the HF
end of the medium wave (where you normally expect to set the aerial
trimmer, peaking up a weak signal at (typically) 1500kHz.

I've got the instruction/installation manual, but there's absolutely no
reference to any aerial trimmer. There might be some form of 'automatic
matching circuit' but, if there is, what does it consist of? You would
need a varicap diode, driven from the AGC line, and some form of servo
loop which would automatically adjust and optimise the diode
capacitance. It all seems a bit complicated - bearing in mind that a
simple aerial trimmer capacitor has been satisfactory for some 60 or 70
years. I just can't see it myself.

I've not researched it so was only a guess. But I've not noticed quality
radios without a trimmer having inferior MW reception than before. Of
course I'm sure there are plenty of cheap units around that are poor - but
then they'll be poor in other ways too. And not surprising given just how
cheap they are these days. I read somewhere 10 dollars is an average for
factory fitted units...

However, don't most cars these days have an 'active' aerial? So any
matching would be done by that pre-amp? Can't think of any new UK supplied
car with the older telescopic type.

--
*Happiness is seeing your mother-in-law on a milk carton

Dave Plowman London SW
To e-mail, change noise into sound.

Michael A. Terrell wrote:
RG/62, 93 ohm coax. The same as what IBM used for their early
computer networks.

I've got some 93 ohm coax lying around from when I used some to make a
matching section. Never knew what the original application was for it.
Very interesting.

Michael A. Terrell wrote:
RG/62, 93 ohm coax. The same as what IBM used for their early
computer networks.

I've got some 93 ohm coax lying around from when I used some to make a
matching section. Never knew what the original application was for it.
Very interesting.

Dave Plowman (News) wrote:
I've not researched it so was only a guess. But I've not noticed quality
radios without a trimmer having inferior MW reception than before.

With the number of stations in the band these days, I find weak signal
performance is rarely the limiting factor. Usually the problem is
selectivity.

This discussion reminds me that my old Mercedes had a momentary contact
built into the power antenna switch that would let you adjust the
antenna length up and down from the dashboard. It was kind of cute but
never seemed to make much difference in reception. (Yet another
example of Germans inventing a problem so that they could solve it, I
think.) The radio itself was an old Blaupunkt and was a magnificent
piece of electronics, though. Vastly overengineered. Automatic
three-stage scan, direct frequency entry, and an alarm clock!

Dave Plowman (News) wrote:
I've not researched it so was only a guess. But I've not noticed quality
radios without a trimmer having inferior MW reception than before.

With the number of stations in the band these days, I find weak signal
performance is rarely the limiting factor. Usually the problem is
selectivity.

This discussion reminds me that my old Mercedes had a momentary contact
built into the power antenna switch that would let you adjust the
antenna length up and down from the dashboard. It was kind of cute but
never seemed to make much difference in reception. (Yet another
example of Germans inventing a problem so that they could solve it, I
think.) The radio itself was an old Blaupunkt and was a magnificent
piece of electronics, though. Vastly overengineered. Automatic
three-stage scan, direct frequency entry, and an alarm clock!

In article ,
David Brodbeck wrote:
This discussion reminds me that my old Mercedes had a momentary contact
built into the power antenna switch that would let you adjust the
antenna length up and down from the dashboard. It was kind of cute but
never seemed to make much difference in reception. (Yet another
example of Germans inventing a problem so that they could solve it, I
think.) The radio itself was an old Blaupunkt and was a magnificent
piece of electronics, though. Vastly overengineered. Automatic
three-stage scan, direct frequency entry, and an alarm clock!

Germany of course had (has) no MW radio transmissions of their own - the
frequencies were removed from them after WW2. Which is why they had such a
lead in FM in the early days. So it might be their radio installations
were also better at receiving distant MW broadcasts.

But the other reason to stop the aerial going fully up was high speed
travel on the autobahn.

--
*Can atheists get insurance for acts of God? *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
David Brodbeck wrote:
This discussion reminds me that my old Mercedes had a momentary contact
built into the power antenna switch that would let you adjust the
antenna length up and down from the dashboard. It was kind of cute but
never seemed to make much difference in reception. (Yet another
example of Germans inventing a problem so that they could solve it, I
think.) The radio itself was an old Blaupunkt and was a magnificent
piece of electronics, though. Vastly overengineered. Automatic
three-stage scan, direct frequency entry, and an alarm clock!

Germany of course had (has) no MW radio transmissions of their own - the
frequencies were removed from them after WW2. Which is why they had such a
lead in FM in the early days. So it might be their radio installations
were also better at receiving distant MW broadcasts.

But the other reason to stop the aerial going fully up was high speed
travel on the autobahn.

--
*Can atheists get insurance for acts of God? *

Dave Plowman London SW
To e-mail, change noise into sound.

On Tue, 01 Dec 2009 14:16:01 -0800, David Brodbeck
wrote:

Dave Plowman (News) wrote:
I've not researched it so was only a guess. But I've not noticed quality
radios without a trimmer having inferior MW reception than before.

With the number of stations in the band these days, I find weak signal
performance is rarely the limiting factor. Usually the problem is
selectivity.

This discussion reminds me that my old Mercedes had a momentary contact
built into the power antenna switch that would let you adjust the
antenna length up and down from the dashboard. It was kind of cute but
never seemed to make much difference in reception. (Yet another
example of Germans inventing a problem so that they could solve it, I
think.) The radio itself was an old Blaupunkt and was a magnificent
piece of electronics, though. Vastly overengineered. Automatic
three-stage scan, direct frequency entry, and an alarm clock!

A good accessory. When I'm driving I like to set my alarm clock to
wake me up every 15 minutes.

On Tue, 01 Dec 2009 14:16:01 -0800, David Brodbeck
wrote:

Dave Plowman (News) wrote:
I've not researched it so was only a guess. But I've not noticed quality
radios without a trimmer having inferior MW reception than before.

With the number of stations in the band these days, I find weak signal
performance is rarely the limiting factor. Usually the problem is
selectivity.

This discussion reminds me that my old Mercedes had a momentary contact
built into the power antenna switch that would let you adjust the
antenna length up and down from the dashboard. It was kind of cute but
never seemed to make much difference in reception. (Yet another
example of Germans inventing a problem so that they could solve it, I
think.) The radio itself was an old Blaupunkt and was a magnificent
piece of electronics, though. Vastly overengineered. Automatic
three-stage scan, direct frequency entry, and an alarm clock!

A good accessory. When I'm driving I like to set my alarm clock to
wake me up every 15 minutes.

On Tue, 01 Dec 2009 14:12:18 -0800, David Brodbeck
wrote:

Michael A. Terrell wrote:
RG/62, 93 ohm coax. The same as what IBM used for their early
computer networks.

I've got some 93 ohm coax lying around from when I used some to make a
matching section. Never knew what the original application was for it.
Very interesting.

RG-62/u was used for Arcnet networking,
http://en.wikipedia.org/wiki/Arcnet
and IBM 3270 terminal systems:
http://en.wikipedia.org/wiki/3270

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Tue, 01 Dec 2009 14:12:18 -0800, David Brodbeck
wrote:

Michael A. Terrell wrote:
RG/62, 93 ohm coax. The same as what IBM used for their early
computer networks.

I've got some 93 ohm coax lying around from when I used some to make a
matching section. Never knew what the original application was for it.
Very interesting.

RG-62/u was used for Arcnet networking,
http://en.wikipedia.org/wiki/Arcnet
and IBM 3270 terminal systems:
http://en.wikipedia.org/wiki/3270

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Wed, 02 Dec 2009 10:11:04 -0500, Meat Plow
wrote:

On Tue, 01 Dec 2009 23:15:32 -0800, Jeff Liebermann
wrote:

On Tue, 01 Dec 2009 14:12:18 -0800, David Brodbeck
wrote:

Michael A. Terrell wrote:
RG/62, 93 ohm coax. The same as what IBM used for their early
computer networks.

I've got some 93 ohm coax lying around from when I used some to make a
matching section. Never knew what the original application was for it.
Very interesting.

RG-62/u was used for Arcnet networking,
http://en.wikipedia.org/wiki/Arcnet
and IBM 3270 terminal systems:
http://en.wikipedia.org/wiki/3270

Ahh, I love the smell of LANtastic over RG62A/U and TCNS in the
morning.

You might want to ease up on whatever you're sniffing. Arcnet and
3270 used BNC connectors. What's a TCNS?

My favorite gizmo was the passive hub. Huge amounts of cash for a
mysterious sealed box with 3 or more BNC connectors. I eventually
dissected one and was rather disappointed to find only a few
resistors.

I'm still not certain that AM/FM car antenna coax cable is RG-62/u. I
haven't found a suitable car antenna to compare with the boxes and
boxes of RG-62/u I have left over from ripping out Arcnet systems
(Lantastic) and replacing them RG-58a/u (Ethernet and Novell).

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:

On Wed, 02 Dec 2009 10:11:04 -0500, Meat Plow
wrote:

On Tue, 01 Dec 2009 23:15:32 -0800, Jeff Liebermann
wrote:

On Tue, 01 Dec 2009 14:12:18 -0800, David Brodbeck
wrote:

Michael A. Terrell wrote:
RG/62, 93 ohm coax. The same as what IBM used for their early
computer networks.

I've got some 93 ohm coax lying around from when I used some to make a
matching section. Never knew what the original application was for it.
Very interesting.

RG-62/u was used for Arcnet networking,
http://en.wikipedia.org/wiki/Arcnet
and IBM 3270 terminal systems:
http://en.wikipedia.org/wiki/3270

Ahh, I love the smell of LANtastic over RG62A/U and TCNS in the
morning.

You might want to ease up on whatever you're sniffing. Arcnet and
3270 used BNC connectors. What's a TCNS?

My favorite gizmo was the passive hub. Huge amounts of cash for a
mysterious sealed box with 3 or more BNC connectors. I eventually
dissected one and was rather disappointed to find only a few
resistors.

I'm still not certain that AM/FM car antenna coax cable is RG-62/u. I
haven't found a suitable car antenna to compare with the boxes and
boxes of RG-62/u I have left over from ripping out Arcnet systems
(Lantastic) and replacing them RG-58a/u (Ethernet and Novell).


Whatever. I heard it from some Delco engineers who designed their
car radios in the '70s, and saw it on plenty of car radio antenna cables
in the '60s & '70s. The Delco engineers explanation was that a whip
antenna for AM was used as a voltage probe, and 93 ohm coax had the
lowest loss available. That made it easier to match to the tuned RF
input. It was also cheap cable with a polypropylene tube to hold the
braid and surround the zigzag center conductor. Compare that to a low
loss teflon which can cost several dollars a foot.


--
The movie 'Deliverance' isn't a documentary!

On Wed, 02 Dec 2009 22:28:14 -0500, "Michael A. Terrell"
wrote:

Whatever. I heard it from some Delco engineers who designed their
car radios in the '70s, and saw it on plenty of car radio antenna cables
in the '60s & '70s.

Sigh. I never bothered to look. I just found a stainless car whip
antenna with coax cable attached. The number on the cable is:
5PT3-30C LCN
Google couldn't find anything. Both ends are soldered so I can't
inspect the guts. The OD is 5.0mm, which is at one end of the range
of RG-62a/u jacket diameters of 5.1 to 6.2mm. I would measure the
PF/ft, but my destroyed my LCR meter is busted. It probably is
RG-62/u but I'm still not convinced.

The Delco engineers explanation was that a whip
antenna for AM was used as a voltage probe, and 93 ohm coax had the
lowest loss available.

Well, let's see. The cable is 4.5ft long.
ohms pf/ft pF
RG-62/u 93 13 58.5
RG-59/u 75 17 76.5
RG-58/u 50 30 135.
Yeah, I can see the reason. The input tuning stage would never tune
with that much capacitance.

That made it easier to match to the tuned RF
input.

Well, it could be matched to almost anything. However, the low coax
capacitance would give the trimmer in the radio a much wider tuning
range.

It was also cheap cable with a polypropylene tube to hold the
braid and surround the zigzag center conductor. Compare that to a low
loss teflon which can cost several dollars a foot.

They didn't PTFE when Bill Lear invented the first "Motorola" car
radio.
http://en.wikipedia.org/wiki/Bill_Lear
Also, at 1MHz, the difference in cable losses between various
dielectrics is zilch at 4.5 ft. They could have used aluminum foil
wrapped garden hose, with a coat hanger as center conductor, and
gotten the same cable loss.






--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com
# http://www.LearnByDestroying.com AE6KS

On Wed, 02 Dec 2009 20:28:15 -0800, Jeff Liebermann
wrote:

They didn't PTFE when Bill Lear invented the first "Motorola" car
radio.

Well, much of this thread is over my head now, sort of, but ftr, I was
40 years old before I realized why it was called "motor-ola"

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

Interesting. For example: Learisms:

# On electronics, "There's only one thing worse than an intermittent,
that's an intermittent intermittent."
# On weight reduction in the Learjet, "I'd sell my grandmother to save
one pound."

On Wed, 02 Dec 2009 23:52:16 -0500, mm
wrote:

On Wed, 02 Dec 2009 20:28:15 -0800, Jeff Liebermann
wrote:

They didn't PTFE when Bill Lear invented the first "Motorola" car
radio.

Well, much of this thread is over my head now, sort of, but ftr, I was
40 years old before I realized why it was called "motor-ola"
http://en.wikipedia.org/wiki/Bill_Lear

In the land mobile biz, it was called Rotomola.

Search Google Patents for "William P. Lear" in order by date:
http://www.google.com/patents?q=%22william%20p.%20lear%22&btnG=Search%20 Patents&scoring=2

There were radios fitted to vehicles before Motorola. However, they
were big and bulky adaptations of console type radios. Together with
the A, B, and C batteries, the radio usually more than one passenger
seat. The antenna was usually a square loop about 4ft in diameter. It
worked, but I wouldn't exactly call it practical. There are photos on
the web, but I'm too lazy to look. By the late 1930's, components had
shrunk sufficiently that to make a small radio. What Bill Lear did
was make it fit in a package that was small enough to be practical in
a car, which included the then unusual minimal rod antenna design.

Here's the original car radio (mounted on the steering column):
http://www.google.com/patents?id=YeZ9AAAAEBAJ
http://www.google.com/patents?id=OkluAAAAEBAJ

Incidentally, many police departments used AM frequencies at the top
of the AM broadcast band for dispatch up to the early 1970's. In Smog
Angeles, listening to the police on a tweaked AM car radio was common.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:

On Wed, 02 Dec 2009 22:28:14 -0500, "Michael A. Terrell"
wrote:

Whatever. I heard it from some Delco engineers who designed their
car radios in the '70s, and saw it on plenty of car radio antenna cables
in the '60s & '70s.

Sigh. I never bothered to look. I just found a stainless car whip
antenna with coax cable attached. The number on the cable is:
5PT3-30C LCN


Sounds like it's from one of many un-named Chinese factories that
churn out crap that almost works. Also, the RG (Radio Guide) standard
was done way with years ago, so even if the cable met the RG/62 specs,
it could have a different marking.


Google couldn't find anything. Both ends are soldered so I can't
inspect the guts. The OD is 5.0mm, which is at one end of the range
of RG-62a/u jacket diameters of 5.1 to 6.2mm. I would measure the
PF/ft, but my destroyed my LCR meter is busted. It probably is
RG-62/u but I'm still not convinced.

The Delco engineers explanation was that a whip
antenna for AM was used as a voltage probe, and 93 ohm coax had the
lowest loss available.

Well, let's see. The cable is 4.5ft long.
ohms pf/ft pF
RG-62/u 93 13 58.5
RG-59/u 75 17 76.5
RG-58/u 50 30 135.
Yeah, I can see the reason. The input tuning stage would never tune
with that much capacitance.

That made it easier to match to the tuned RF
input.

Well, it could be matched to almost anything. However, the low coax
capacitance would give the trimmer in the radio a much wider tuning
range.

It was also cheap cable with a polypropylene tube to hold the
braid and surround the zigzag center conductor. Compare that to a low
loss teflon which can cost several dollars a foot.

They didn't PTFE when Bill Lear invented the first "Motorola" car
radio.
http://en.wikipedia.org/wiki/Bill_Lear


So? I never said it did. I was comparing the quality. They
continued to use the same RG/62 coax, even when alternatives became
available.


Also, at 1MHz, the difference in cable losses between various
dielectrics is zilch at 4.5 ft. They could have used aluminum foil
wrapped garden hose, with a coat hanger as center conductor, and
gotten the same cable loss.


Who would use crap like that, when a ready made cable was available
COTS? Who would want to screw with trying to route that through a
fender, and under the dash? That is the worst straw man I've ever seen.

BTW, I have seen cheap replacement car radio antennas made with RG-58
and they were crap on FM. Of course they were only $3 each by the case
of 25 and a lot of half assed installers used them. The shop had a pile
of craptennas that were removed to install what belonged on the various
cars & trucks we serviced. They would have filled a 55 gallon drum.


The first car radios used an antenna under the running board. There
were many changes over the decades.


--
The movie 'Deliverance' isn't a documentary!

Meat Plow wrote:
On Tue, 01 Dec 2009 23:15:32 -0800, Jeff Liebermann
wrote:

On Tue, 01 Dec 2009 14:12:18 -0800, David Brodbeck
wrote:

Michael A. Terrell wrote:
RG/62, 93 ohm coax. The same as what IBM used for their early
computer networks.
I've got some 93 ohm coax lying around from when I used some to make a
matching section. Never knew what the original application was for it.
Very interesting.
RG-62/u was used for Arcnet networking,
http://en.wikipedia.org/wiki/Arcnet
and IBM 3270 terminal systems:
http://en.wikipedia.org/wiki/3270

Ahh, I love the smell of LANtastic over RG62A/U and TCNS in the
morning.

Do you happen to have any of the TCNS 100Mbit adapters?

Michael

Jeff Liebermann wrote:
snip

What's a TCNS?

Thomas-Conrad Network -- I am particularly interested in
the 100Mbps version and in finding NICs for it (I have
an old ad-insertion system that outputs on 100Mbit TCNS
and I actually am considering doing 100Mbit over RG69
which was previously laid underground for CATV distribution.

Michael

Jeff Liebermann wrote:
Incidentally, many police departments used AM frequencies at the top
of the AM broadcast band for dispatch up to the early 1970's. In Smog
Angeles, listening to the police on a tweaked AM car radio was common.

My grandparents have a Philco console set from the 1930s that has that
police band marked on the dial.

mm wrote:
A good accessory. When I'm driving I like to set my alarm clock to
wake me up every 15 minutes.

Yeah, that was my reaction at first, too. Later I found it was actually
quite useful when taking short "safety naps" at rest stops. A 15 minute
nap does wonders when I'm feeling not so alert in the afternoon.
'Course nowadays I just use the alarm clock feature of my cell phone.

David Brodbeck wrote:

Jeff Liebermann wrote:
Incidentally, many police departments used AM frequencies at the top
of the AM broadcast band for dispatch up to the early 1970's. In Smog
Angeles, listening to the police on a tweaked AM car radio was common.

My grandparents have a Philco console set from the 1930s that has that
police band marked on the dial.

Yes, but it was one way communications from the police station to the
police cars, and was right above the AM BCB. They used 'Police Call
boxes' to contact the dispatcher. They were telephones in locked metal
boxes that ran directly to the dispatcher's office.


--
Offworld checks no longer accepted!