Interference in FM radio reception.

[Jeff Liebermann]

On Sun, 08 Jan 2012 19:09:39 -0500, micky <NONONOmisc07@bigfoot.com>
wrote:

I have to say, this sounds like the opening scene from a murder
mystery. Only cars are big enough to start the lights.

Nope. They respond to people. I park there all the time. As I
vaguely recall, the motion sensors are located about half way up the
light poles. They take a few seconds to come on to full brightness,
and likewise, fade slowly when they turn off. Since the parking lot
lights are independently controlled, it's possible to have them come
on in sequence as one walks slowly across the lot.

The woman
parks the car, away from the entrance so other cars won't ding hers.
She walks to the store, is almost there, remembers sometihing in the
car and has to go back, and on her second trip to the store, the
parking lot lights go off, and she hears footsteps behind her. We
only see her legs and his legs, and soon they are both running.

Considering the time of day and the neighborhood, that's quite likely.
Fortunately, having the lights come on when the prospective car thief
enters the parking lot tends to provide a rather strong deterrent.

In the next scene, there are a lot of police standing around.

Possibly. The city police station is about 200 meters away.

The problem with finding sources of interference and such is the
hardware required. I used to do quite a bit of wi-fi sniffing,
searching for various sources of interference, leeches, hackers, DoS
sources, over-powered radios, and such. Same with searching for stuck
transmitters on commercial frequencies, foreign fishermen on US
frequencies, unlicensed operators, and premature LPFM stations. While
the equipment varies, it always seems to attract the attention of the
authorities. Walking through a busy shopping center parking lot, with
a fiberglass pole, topped with a small dish antenna, dragging a pile
of black boxes, with my face glued to a laptop. To the average
shopper, I was a cross between a terrorist and a visiting
intergalactic alien. No melodrama, but plenty of answering really
dumb questions. After a while, I learned to think first, and search
after. Have fun finding the interference source.

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

 

[micky]

On Sun, 08 Jan 2012 17:59:19 -0800, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Sun, 08 Jan 2012 19:09:39 -0500, micky <NONONOmisc07@bigfoot.com
wrote:

I have to say, this sounds like the opening scene from a murder
mystery. Only cars are big enough to start the lights.

Nope. They respond to people.

Dramatic license.

I park there all the time. As I
vaguely recall, the motion sensors are located about half way up the
light poles. They take a few seconds to come on to full brightness,
and likewise, fade slowly when they turn off. Since the parking lot
lights are independently controlled, it's possible to have them come
on in sequence as one walks slowly across the lot.

The woman
parks the car, away from the entrance so other cars won't ding hers.
She walks to the store, is almost there, remembers sometihing in the
car and has to go back, and on her second trip to the store, the
parking lot lights go off, and she hears footsteps behind her. We
only see her legs and his legs, and soon they are both running.

Considering the time of day and the neighborhood, that's quite likely.
Fortunately, having the lights come on when the prospective car thief
enters the parking lot tends to provide a rather strong deterrent.

If you want to sell this script, we're going to have to change some
things. If you won't cooperate, I'm not going to let you know when
the meeting is.

In the next scene, there are a lot of police standing around.

Possibly. The city police station is about 200 meters away.

The problem with finding sources of interference and such is the
hardware required. I used to do quite a bit of wi-fi sniffing,
searching for various sources of interference, leeches, hackers, DoS
sources, over-powered radios, and such. Same with searching for stuck
transmitters on commercial frequencies, foreign fishermen on US
frequencies, unlicensed operators, and premature LPFM stations. While
the equipment varies, it always seems to attract the attention of the
authorities. Walking through a busy shopping center parking lot, with
a fiberglass pole, topped with a small dish antenna, dragging a pile
of black boxes, with my face glued to a laptop. To the average
shopper, I was a cross between a terrorist and a visiting
intergalactic alien.

I'll bet!

No melodrama, but plenty of answering really
dumb questions. After a while, I learned to think first, and search
after. Have fun finding the interference source.

Thanks. I'll let you know how it goes. Though I've lost some
interest in finding the interfernce, and I'm turning my attention to
finishing the script and shopping it around.

 

[Jeff Liebermann]

On Mon, 09 Jan 2012 00:01:58 -0500, micky <NONONOmisc07@bigfoot.com>
wrote:

Dramatic license.

I prefer poetic license:
<http://www.LearnByDestroying.com/poetry/poetry.htm>

If you're going to sell this script, it will need drama, suspense,
action, intrigue, politics, explosions, violence, a chase scene, sex,
and display the advertisers products. However, the one thing that
must never appear in the script is something that requires the viewer
to think. If there's even the slightest hint of "how does that
work?", the script won't sell. Science fiction and defective physics
are perfectly acceptable, as long as the actors all pretend that it's
real, and that nobody in the story questions the technology. To many
people, microprocessor controlled parking lot lights, triggered by
sophisticated PIR detectors, are more like magic than science.

I forgot to mention that the lights were all LED lights and VERY
bright. Something like this:
<http://www.ledsmagazine.com/news/6/1/13>
The real question is whether LED lights generate RF interference.
There's no consensus and plenty of opinions. My experience has been
that some do, and some don't. I have several consumer LED house
lights. Only one belches RFI. I haven't bothered to check which ones
are boost, buck, or both.
<http://prudentrver.typepad.com/leds/2011/03/reasons-an-led-light-might-emit-radio-frequency-interference.html>


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

 

[klem kedidelhopper]

On Jan 9, 2:50 am, Jeff Liebermann <je...@cruzio.com> wrote:

On Mon, 09 Jan 2012 00:01:58 -0500, micky <NONONOmis...@bigfoot.com
wrote:

Dramatic license.

I prefer poetic license:
http://www.LearnByDestroying.com/poetry/poetry.htm

If you're going to sell this script, it will need drama, suspense,
action, intrigue, politics, explosions, violence, a chase scene, sex,
and display the advertisers products.  However, the one thing that
must never appear in the script is something that requires the viewer
to think.  If there's even the slightest hint of "how does that
work?", the script won't sell.  Science fiction and defective physics
are perfectly acceptable, as long as the actors all pretend that it's
real, and that nobody in the story questions the technology.  To many
people, microprocessor controlled parking lot lights, triggered by
sophisticated PIR detectors, are more like magic than science.

I forgot to mention that the lights were all LED lights and VERY
bright.  Something like this:
http://www.ledsmagazine.com/news/6/1/13
The real question is whether LED lights generate RF interference.
There's no consensus and plenty of opinions.  My experience has been
that some do, and some don't.  I have several consumer LED house
lights.  Only one belches RFI.  I haven't bothered to check which ones
are boost, buck, or both.
http://prudentrver.typepad.com/leds/2011/03/reasons-an-led-light-migh...

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

I live in a small town in New Hampshire. About twenty years ago,
(before we got cable into town) I suddenly started to get numerous
calls from customers on one side of town complaining that TV channel 5
had just simply disappeared. My house was not affected and so this was
news to me. I visited one affected house and found a grey screen with
no audio. It appeared as though something was completely swamping the
entire channel. We contacted the FCC in Boston and what a waste of
time that was.
So I drove around town visiting different homes and asking if they
were also affected by this. Eventually I was able to draw a sort of
"lobe" of the pattern. The pattern was somewhat directional and the
radiating point appeared to be a communications tower set on private
property. The gentleman that owned the tower was very proud of it and
took me on a short tour of the facility. He would lease parts of this
tower to different commercial services. Among these services was a
radio data link to Massachusetts which operated on a frequency 200KHZ
below channel five's video carrier. While in the shack I noticed a
bandpass filter sitting on the shelf which was marked with his
operating frequency. I asked if that shouldn't have been in line with
the antenna and at that point the meeting became adversarial. I often
wondered if perhaps the filter was tuned incorrectly and it's
insertion into the line caused problems, so that was why he removed
it, or perhaps he was overmodulating, creating excessive sidebands
which poked into channel five. In any case I found it interesting
though that a few days after my visit the problem mysteriously
disappeared , never to return again.
When I was fifteen I built my first kit, an Eico CB radio. The
receiver was as wide as a barn door but it had an excellent
transmitter section. We lived in an apartment building in the Bronx
and most television sets of the day were built with 21MHZ IF strips.
So when I keyed that transmitter no one for blocks around was able to
watch channel two on their TV sets. I installed a low pass fiIter on
my rig and I lost track of how many high pass filters I installed for
my neighbors.
I would also think about your radio's IF frequency, although on second
thought that would not be limited to only certain channels.
I'd really like to know if you find this thing. Please keep us
informed. Lenny

 

[Jeff Liebermann]

On Wed, 11 Jan 2012 08:07:47 -0800 (PST), klem kedidelhopper
<captainvideo462009@gmail.com> wrote:

I live in a small town in New Hampshire. About twenty years ago,
(before we got cable into town) I suddenly started to get numerous
calls from customers on one side of town complaining that TV channel 5
had just simply disappeared.

Many such TV's had AFC (automagic frequency control). Give it a
strong nearby carrier, and it will lock on the carrier instead of the
TV signal carrier.

So I drove around town visiting different homes and asking if they
were also affected by this. Eventually I was able to draw a sort of
"lobe" of the pattern.

Nicely done. That sounds like quite a bit of work.

Among these services was a
radio data link to Massachusetts which operated on a frequency 200KHZ
below channel five's video carrier.

It had to be more than 200Khz. Channel 5 video is at 77.25MHz. The
75MHz "telemetry and radio control" band is roughly from 75 to 76MHz.
It would need to be more like 2MHz below the CH5 carrier. Still, for
a 6MHz wide TV signal, that's quite close if running high power.
However, as I recall (and am too lazy to lookup), the highest power
allowed at 75MHz is something like 1 watt. I don't think it was a
filter, but rather far too much power.

While in the shack I noticed a
bandpass filter sitting on the shelf which was marked with his
operating frequency. I asked if that shouldn't have been in line with
the antenna and at that point the meeting became adversarial.

Nice detective work. I once gave a visiting FCC inspector an
"unofficial" tour of our mountain top radio site. I explained
everything and answered many questions. In gratitude, he sent about
100 "failure to post licenses" and other administrivia violations, not
to the service company, but directly to the customers. That didn't
cost much in fines, but as a result, we lost a few customers. I don't
give tours any more.

I often
wondered if perhaps the filter was tuned incorrectly and it's
insertion into the line caused problems, so that was why he removed
it, or perhaps he was overmodulating, creating excessive sidebands
which poked into channel five.

My guess is that he was running too much power trying to span the
distance between NH and Boston. Adding the filter probably increased
the loss to the point where the link failed. My guess is that it was
taken off the air when the site owner discovered what was happening.

When I was fifteen I built my first kit, an Eico CB radio. The
receiver was as wide as a barn door but it had an excellent
transmitter section. We lived in an apartment building in the Bronx
and most television sets of the day were built with 21MHZ IF strips.
So when I keyed that transmitter no one for blocks around was able to
watch channel two on their TV sets. I installed a low pass fiIter on
my rig and I lost track of how many high pass filters I installed for
my neighbors.

Ummm... you have it somewhat wrong. The hi pass filter goes on the 27
MHz xmitter, in order to remove any spurious rubbish from the transmit
signal at 21.4MHz. A low pass filter would NOT work on the TV set as
the frequency range is 54 to 800MHz and a low pass filter would block
all of it. However, a 21MHz notch filter on the antenna would work
wonders.

Incidentally, I helped an older friend build the same EICO CB radio.
The tunable receiver was horrible, but at the time, I didn't know
quality when I saw it.
<http://www.radiomuseum.org/r/eico_770770.html>

I would also think about your radio's IF frequency, although on second
thought that would not be limited to only certain channels.
I'd really like to know if you find this thing. Please keep us
informed. Lenny

Unless the front end is broadband and crude, the IF rejection of
modern receivers is quite good.

For 2.4GHz, the last device that used an IF frequency was the ancient
Lucent chipset and possible the early IBM wireless oddities. Literally
everything for the last 10 years or so has been direct conversion,
with no IF frequency. Google for "802.11 direct conversion receiver"
for hundreds of examples. IF feedthrough is unlikely if there's no
IF.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Jeff Liebermann]

On Wed, 11 Jan 2012 09:18:11 -0800, Jeff Liebermann <jeffl@cruzio.com>
wrote:

Ummm... you have it somewhat wrong. The hi pass filter goes on the 27
MHz xmitter, in order to remove any spurious rubbish from the transmit
signal at 21.4MHz. A low pass filter would NOT work on the TV set as
the frequency range is 54 to 800MHz and a low pass filter would block
all of it. However, a 21MHz notch filter on the antenna would work
wonders.

Argh. That's all wrong. I somehow merged the 21.4IF feedthru problem
with the CB harmonic filter. The lo-pass filter should be on the CB
xmitter, to reduce the 2nd harmonic that trashed Channel 2. The 54MHz
high pass filter goes on TV, to keep the CB radio from generating
harmonics in the tuner section.

Remind me not to post anything before my morning coffee fix.

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

 

[klem kedidelhopper]

On Jan 11, 12:18 pm, Jeff Liebermann <je...@cruzio.com> wrote:

On Wed, 11 Jan 2012 08:07:47 -0800 (PST), klem kedidelhopper

captainvideo462...@gmail.com> wrote:
I live in a small town in New Hampshire. About twenty years ago,
(before we got cable into town) I suddenly started to get numerous
calls from customers on one side of town complaining that TV channel 5
had just simply disappeared.

Many such TV's had AFC (automagic frequency control).  Give it a
strong nearby carrier, and it will lock on the carrier instead of the
TV signal carrier.

So I drove around town visiting different homes and asking if they
were also affected by this. Eventually I was able to draw a sort of
"lobe" of the pattern.

Nicely done.  That sounds like quite a bit of work.

Among these services was a
radio data link to Massachusetts which operated on a frequency 200KHZ
below channel five's video carrier.

It had to be more than 200Khz.  Channel 5 video is at 77.25MHz.  The
75MHz "telemetry and radio control" band is roughly from 75 to 76MHz.
It would need to be more like 2MHz below the CH5 carrier.  Still, for
a 6MHz wide TV signal, that's quite close if running high power.
However, as I recall (and am too lazy to lookup), the highest power
allowed at 75MHz is something like 1 watt.  I don't think it was a
filter, but rather far too much power.

While in the shack I noticed a
bandpass filter sitting on the shelf which was marked with his
operating frequency. I asked if that shouldn't have been in line with
the antenna and at that point the meeting became adversarial.

Nice detective work.  I once gave a visiting FCC inspector an
"unofficial" tour of our mountain top radio site.  I explained
everything and answered many questions.  In gratitude, he sent about
100 "failure to post licenses" and other administrivia violations, not
to the service company, but directly to the customers.  That didn't
cost much in fines, but as a result, we lost a few customers.  I don't
give tours any more.

I often
wondered if perhaps the filter was tuned incorrectly and it's
insertion into the line caused problems, so that was why he removed
it, or perhaps he was overmodulating, creating excessive sidebands
which poked into channel five.

My guess is that he was running too much power trying to span the
distance between NH and Boston.  Adding the filter probably increased
the loss to the point where the link failed.  My guess is that it was
taken off the air when the site owner discovered what was happening.

When I was fifteen I  built my first kit, an Eico CB radio. The
receiver was as wide as a barn door but it had an excellent
transmitter section. We lived in an apartment building in the Bronx
and most television sets of the day were built with 21MHZ IF strips.
So when I keyed that transmitter no one for blocks around was able to
watch channel two on their TV sets. I installed a low pass fiIter on
my rig and I lost track of how many high pass filters I installed for
my neighbors.

Ummm... you have it somewhat wrong.  The hi pass filter goes on the 27
MHz xmitter, in order to remove any spurious rubbish from the transmit
signal at 21.4MHz.  A low pass filter would NOT work on the TV set as
the frequency range is 54 to 800MHz and a low pass filter would block
all of it.  However, a 21MHz notch filter on the antenna would work
wonders.

Incidentally, I helped an older friend build the same EICO CB radio.
The tunable receiver was horrible, but at the time, I didn't know
quality when I saw it.
http://www.radiomuseum.org/r/eico_770770.html

I would also think about your radio's IF frequency, although on second
thought that would not be limited to only certain channels.
I'd really like to know if you find this thing. Please keep us
informed. Lenny

Unless the front end is broadband and crude, the IF rejection of
modern receivers is quite good.

For 2.4GHz, the last device that used an IF frequency was the ancient
Lucent chipset and possible the early IBM wireless oddities. Literally
everything for the last 10 years or so has been direct conversion,
with no IF frequency.  Google for "802.11 direct conversion receiver"
for hundreds of examples.  IF feedthrough is unlikely if there's no
IF.
--
Jeff Liebermann     je...@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Thanks for your comments Jeff. You're correct about the filters. I had
them reversed. And the Radio museum page is close. I think the 770
was four or five channels of crystal control transmit. My rig was
the 760 and I built two of them. Initially it had only one crystal for
transmit. I had to cut a small window out of the back near the crystal
socket so that I could change crystals. It was a pain and truly kind
of short sighted on Eico's part. They also offered (I think the model
was a 775) with a vibrator power supply. I eventually installed 23
crystals and a switch in a box underneath the radio to accommodate all
channels. I also bought the special transformer, vibrator and other
necessary components to convert my rig for mobile use. Ultimately the
vibrator proved to be much too noisy and I replaced it with a blocking
oscillator circuit built around a 400HZ power transformer. Probably
wasn't very efficient but It It worked well, it was QUIET and it just
happened to put out the 275V B+ that the radio required. I have great
memories of bombing around The Bronx in 1966 with my CB and 102 inch
whip antenna in my 1953 Desoto. Incidentally I went on to work for
Eico as a QC technician a few years later for a short period too.
Lenny

 

[klem kedidelhopper]

On Jan 11, 12:18 pm, Jeff Liebermann <je...@cruzio.com> wrote:

On Wed, 11 Jan 2012 08:07:47 -0800 (PST), klem kedidelhopper

captainvideo462...@gmail.com> wrote:
I live in a small town in New Hampshire. About twenty years ago,
(before we got cable into town) I suddenly started to get numerous
calls from customers on one side of town complaining that TV channel 5
had just simply disappeared.

Many such TV's had AFC (automagic frequency control).  Give it a
strong nearby carrier, and it will lock on the carrier instead of the
TV signal carrier.

So I drove around town visiting different homes and asking if they
were also affected by this. Eventually I was able to draw a sort of
"lobe" of the pattern.

Nicely done.  That sounds like quite a bit of work.

Among these services was a
radio data link to Massachusetts which operated on a frequency 200KHZ
below channel five's video carrier.

It had to be more than 200Khz.  Channel 5 video is at 77.25MHz.  The
75MHz "telemetry and radio control" band is roughly from 75 to 76MHz.
It would need to be more like 2MHz below the CH5 carrier.  Still, for
a 6MHz wide TV signal, that's quite close if running high power.
However, as I recall (and am too lazy to lookup), the highest power
allowed at 75MHz is something like 1 watt.  I don't think it was a
filter, but rather far too much power.

While in the shack I noticed a
bandpass filter sitting on the shelf which was marked with his
operating frequency. I asked if that shouldn't have been in line with
the antenna and at that point the meeting became adversarial.

Nice detective work.  I once gave a visiting FCC inspector an
"unofficial" tour of our mountain top radio site.  I explained
everything and answered many questions.  In gratitude, he sent about
100 "failure to post licenses" and other administrivia violations, not
to the service company, but directly to the customers.  That didn't
cost much in fines, but as a result, we lost a few customers.  I don't
give tours any more.

I often
wondered if perhaps the filter was tuned incorrectly and it's
insertion into the line caused problems, so that was why he removed
it, or perhaps he was overmodulating, creating excessive sidebands
which poked into channel five.

My guess is that he was running too much power trying to span the
distance between NH and Boston.  Adding the filter probably increased
the loss to the point where the link failed.  My guess is that it was
taken off the air when the site owner discovered what was happening.

When I was fifteen I  built my first kit, an Eico CB radio. The
receiver was as wide as a barn door but it had an excellent
transmitter section. We lived in an apartment building in the Bronx
and most television sets of the day were built with 21MHZ IF strips.
So when I keyed that transmitter no one for blocks around was able to
watch channel two on their TV sets. I installed a low pass fiIter on
my rig and I lost track of how many high pass filters I installed for
my neighbors.

Ummm... you have it somewhat wrong.  The hi pass filter goes on the 27
MHz xmitter, in order to remove any spurious rubbish from the transmit
signal at 21.4MHz.  A low pass filter would NOT work on the TV set as
the frequency range is 54 to 800MHz and a low pass filter would block
all of it.  However, a 21MHz notch filter on the antenna would work
wonders.

Incidentally, I helped an older friend build the same EICO CB radio.
The tunable receiver was horrible, but at the time, I didn't know
quality when I saw it.
http://www.radiomuseum.org/r/eico_770770.html

I would also think about your radio's IF frequency, although on second
thought that would not be limited to only certain channels.
I'd really like to know if you find this thing. Please keep us
informed. Lenny

Unless the front end is broadband and crude, the IF rejection of
modern receivers is quite good.

For 2.4GHz, the last device that used an IF frequency was the ancient
Lucent chipset and possible the early IBM wireless oddities. Literally
everything for the last 10 years or so has been direct conversion,
with no IF frequency.  Google for "802.11 direct conversion receiver"
for hundreds of examples.  IF feedthrough is unlikely if there's no
IF.
--
Jeff Liebermann     je...@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Thanks for your comments Jeff. You're correct about the filters. I had
them reversed. And the Radio museum page is close. I think the 770
was four or five channels of crystal control transmit. My rig was
the 760 and I built two of them. Initially it had only one crystal for
transmit. I had to cut a small window out of the back near the crystal
socket so that I could change crystals. It was a pain and truly kind
of short sighted on Eico's part. They also offered (I think the model
was a 775) with a vibrator power supply. I eventually installed 23
crystals and a switch in a box underneath the radio to accommodate all
channels. I also bought the special transformer, vibrator and other
necessary components to convert my rig for mobile use. Ultimately the
vibrator proved to be much too noisy and I replaced it with a blocking
oscillator circuit built around a 400HZ power transformer. Probably
wasn't very efficient but It It worked well, it was QUIET and it just
happened to put out the 275V B+ that the radio required. I have great
memories of bombing around The Bronx in 1966 with my CB and 102 inch
whip antenna in my 1953 Desoto. Incidentally I went on to work for
Eico as a QC technician a few years later for a short period too.
Lenny

 

[josephkk]

On Wed, 11 Jan 2012 10:27:50 -0800, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Wed, 11 Jan 2012 09:18:11 -0800, Jeff Liebermann <jeffl@cruzio.com
wrote:

Ummm... you have it somewhat wrong. The hi pass filter goes on the 27
MHz xmitter, in order to remove any spurious rubbish from the transmit
signal at 21.4MHz. A low pass filter would NOT work on the TV set as
the frequency range is 54 to 800MHz and a low pass filter would block
all of it. However, a 21MHz notch filter on the antenna would work
wonders.

Argh. That's all wrong. I somehow merged the 21.4IF feedthru problem
with the CB harmonic filter. The lo-pass filter should be on the CB
xmitter, to reduce the 2nd harmonic that trashed Channel 2. The 54MHz
high pass filter goes on TV, to keep the CB radio from generating
harmonics in the tuner section.

Remind me not to post anything before my morning coffee fix.

Y0u had me worried there.

?-)

 

[klem kedidelhopper]

On Jan 13, 9:20 pm, josephkk <joseph_barr...@sbcglobal.net> wrote:

On Wed, 11 Jan 2012 10:27:50 -0800, Jeff Liebermann <je...@cruzio.com
wrote:



On Wed, 11 Jan 2012 09:18:11 -0800, Jeff Liebermann <je...@cruzio.com
wrote:

Ummm... you have it somewhat wrong.  The hi pass filter goes on the 27
MHz xmitter, in order to remove any spurious rubbish from the transmit
signal at 21.4MHz.  A low pass filter would NOT work on the TV set as
the frequency range is 54 to 800MHz and a low pass filter would block
all of it.  However, a 21MHz notch filter on the antenna would work
wonders.

Argh.  That's all wrong.  I somehow merged the 21.4IF feedthru problem
with the CB harmonic filter.  The lo-pass filter should be on the CB
xmitter, to reduce the 2nd harmonic that trashed Channel 2.  The 54MHz
high pass filter goes on TV, to keep the CB radio from generating
harmonics in the tuner section.

Remind me not to post anything before my morning coffee fix.

Y0u had me worried there.

?-)
Sometimes I worry myself. I thought they were right the first time but

I guess I am a bit foggy sometimes. Save some coffee for me too, OK?
Lenny

 

[Jeff Liebermann]

On Fri, 13 Jan 2012 18:20:40 -0800, josephkk
<joseph_barrett@sbcglobal.net> wrote:

Remind me not to post anything before my morning coffee fix.

Y0u had me worried there.
?-)

The effect is psychological. One sip of coffee has the same effect as
drinking the whole cup. Whatever the mechanism, I find it difficult
to think clearly before my morning fix. Never mind that I'm also
reading email, replying to email, talking on the phone, planning my
day, dealing with paperwork, yacking on the ham radio, cleaning house,
reading a magazine, watching TV, and assembling lunch at the same
time. Simultaneously doing 10 things badly, takes less time than
sequentially doing each correctly.

To error is human, and I sometimes need to reassure myself that I'm
still human.

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