P
Phil Allison
Guest
** Who is this "you" - white man ?
The tube FM receiver was made in USA ( mono, 75uS de-emphasis) and used a 12AT7 local oscillator - barely able to run at 100MHz.
..... Phil
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** Who is this "you" - white man ?
The tube FM receiver was made in USA ( mono, 75uS de-emphasis) and used a 12AT7 local oscillator - barely able to run at 100MHz.
..... Phil
I
Ian Jackson
Guest
In message <m2rf4b$1av$1@dont-email.me>, William Sommerwerck
<grizzledgeezer@comcast.net> writes
Even with the local oscillator above the station frequency, if you're
near an airport, you can get the air traffic control traffic (120MHz +/-
quite a lot) breaking through - especially if the planes are passing
more-or-less overhead. My kitchen radio gets hit when it's tuned to
97.3MHz, by out-bound flights which have just taken off from London
Heathrow, on around 118.7MHz. But, of course, it all depends on the
'front end' selectivity of the radio. However, this doesn't explain the
OP's problem - which indeed does sound as if it's simply that the same
program being carried by more than one transmitter.
--
Ian
<grizzledgeezer@comcast.net> writes
"Ian Jackson" wrote in message
news:0iUda0GN0QUUFwOM@g3ohx.demon.co.uk...
I'm pretty sure that the local oscillator nearly always runs 10.7MHz
HIGHER than the radio signal.
Precisely If it were lower, you'd greatly increase the possibility of images.
Even with the local oscillator above the station frequency, if you're
near an airport, you can get the air traffic control traffic (120MHz +/-
quite a lot) breaking through - especially if the planes are passing
more-or-less overhead. My kitchen radio gets hit when it's tuned to
97.3MHz, by out-bound flights which have just taken off from London
Heathrow, on around 118.7MHz. But, of course, it all depends on the
'front end' selectivity of the radio. However, this doesn't explain the
OP's problem - which indeed does sound as if it's simply that the same
program being carried by more than one transmitter.
--
Ian
M
Michael Black
Guest
On Wed, 29 Oct 2014, William Sommerwerck wrote:
where fewer strong signals are?
You don't want images to be below the FM broadcast band, then you end up
with TV stations 2 through 6. But above the FM broadcast band, you get a
decent stretch of aero band, amateur radio, public service, weather.
Channel 7 doesn't start until somewhere above all that.
Michael
Isn't it more precisely, that by putting the LO higher, the image falls"Ian Jackson" wrote in message news:0iUda0GN0QUUFwOM@g3ohx.demon.co.uk...
I'm pretty sure that the local oscillator nearly always runs 10.7MHz HIGHER
than the radio signal.
Precisely If it were lower, you'd greatly increase the possibility of
images.
where fewer strong signals are?
You don't want images to be below the FM broadcast band, then you end up
with TV stations 2 through 6. But above the FM broadcast band, you get a
decent stretch of aero band, amateur radio, public service, weather.
Channel 7 doesn't start until somewhere above all that.
Michael
P
Phil Allison
Guest
micky wrote:
** What make and model radio is doing this ??
Does it have a TDA7000 IC inside, by any chance ??
Those have an internal IF frequency of only 70KHz and image rejection is by purest magic.
FYI:
If this problem exists on only one radio, it must be the fault of that radio.
FYI 2
Your post is 99% incomprehensible drivel.
.... Phil
How can the same FM station appear at two different spots on the dial?
Where I live there are two FM radio stations, 88.1 which is only a few
miles away, and 88.5 which is 40 or 50 miles away.
Right now, only my expensive KLM radio plus any car radio gets the
second one well, but I've had some cheap radios that do almost as well.
I lose track of which radios those are, so I'll start tuning at 88.1 and
tune up very gradually. After a period of silence, when I get above
88.5 to what I'd estimate is 88.6 or .7 or .8 I get 88.1 again.
** What make and model radio is doing this ??
Does it have a TDA7000 IC inside, by any chance ??
Those have an internal IF frequency of only 70KHz and image rejection is by purest magic.
FYI:
If this problem exists on only one radio, it must be the fault of that radio.
FYI 2
Your post is 99% incomprehensible drivel.
.... Phil
How is that happening? I know about harmonics, but that doesn't apply,
does it?
P.S. This means 88.5 doesn't come in at all. I've tried stretching
out the power cord, which on the cheap radios is usually the antenna.
Sometimes that helps but on most of the radios, 88.5 won't come in at
all.
P.P.S. 88.1 is WYPR Baltimore. 88.5 is WAMU in DC. Sometimes they
play the same thing, like during the top of the hour news, Diane Rehm,
etc. although WAMU is on a 5 or 10 second delay most of the time.
Because the topic and the voices can be the same it means I can't tell
for a while if I've gotten 88.5 or just another 'instance' of 88.1.
W
William Sommerwerck
Guest
"Michael Black" wrote in message
news:alpine.LNX.2.02.1410291558180.4171@darkstar.example.org...
On Wed, 29 Oct 2014, William Sommerwerck wrote:
That would depend on band allocations and transmitter power. I'm thinking of
images from within the FM band.
Given that the FM band is 20MHz, and twice 10.7 MHz is greater than 20MHz, if
the LO is above the incoming signal, images would come from stations above
107.9MHz (outside the band). If the LO were below the incoming signal, you
could have in-band images starting at 98.9MHz.
news:alpine.LNX.2.02.1410291558180.4171@darkstar.example.org...
On Wed, 29 Oct 2014, William Sommerwerck wrote:
Precisely. If it were lower, you'd greatly increase the possibility of
images.
Isn't it more precisely, that by putting the LO higher, the image falls
where fewer strong signals are?
That would depend on band allocations and transmitter power. I'm thinking of
images from within the FM band.
Given that the FM band is 20MHz, and twice 10.7 MHz is greater than 20MHz, if
the LO is above the incoming signal, images would come from stations above
107.9MHz (outside the band). If the LO were below the incoming signal, you
could have in-band images starting at 98.9MHz.
I
Ian Jackson
Guest
In message <m2ri8g$e6a$1@dont-email.me>, William Sommerwerck
<grizzledgeezer@comcast.net> writes
No. Taking the upper band edge as 108, 108 - 2x10.7 = 86.6 (well below
the lower band edge). This is within old US TV channel 6 - and as you
tune lower, you will hit channel 5.
--
Ian
<grizzledgeezer@comcast.net> writes
"Michael Black" wrote in message
news:alpine.LNX.2.02.1410291558180.4171@darkstar.example.org...
On Wed, 29 Oct 2014, William Sommerwerck wrote:
Precisely. If it were lower, you'd greatly increase the possibility
of images.
Isn't it more precisely, that by putting the LO higher, the image
falls where fewer strong signals are?
That would depend on band allocations and transmitter power. I'm
thinking of images from within the FM band.
Given that the FM band is 20MHz, and twice 10.7 MHz is greater than
20MHz, if the LO is above the incoming signal, images would come from
stations above 107.9MHz (outside the band). If the LO were below the
incoming signal, you could have in-band images starting at 98.9MHz.
No. Taking the upper band edge as 108, 108 - 2x10.7 = 86.6 (well below
the lower band edge). This is within old US TV channel 6 - and as you
tune lower, you will hit channel 5.
--
Ian
I
Ian Jackson
Guest
In message <bc626660-d1bb-45a0-88d8-ff0d9dadfea2@googlegroups.com>, Phil
Allison <pallison49@gmail.com> writes
Then don't you get a lot of image trouble from the two TV channels below
the FM band?
I would think the benefit would be pretty marginal.
While I'm sure there are exceptions, regardless of the frequency they're
receiving, there are probably very few 'normal' radios or TV sets etc
where the LO runs below the tuned frequency.
--
Ian
Allison <pallison49@gmail.com> writes
Ian Jackson wrote:
** Not really possible since the FM band is only 20MHz wide.
For a low side local osc:
88.1-10.7 = 77.4 = lowest local osc f
77.4+20.0 = 97.4 = highest local osc f
97.4+10.7 = 108.1 = higher f than any station.
I'm pretty sure that the local oscillator nearly always runs 10.7MHz
HIGHER than the radio signal.
** In the examples I have checked ( both tube and SS ), it was always
10.7MHz lower.
Then don't you get a lot of image trouble from the two TV channels below
the FM band?
Makes the LO more stable is one reason.
I would think the benefit would be pretty marginal.
While I'm sure there are exceptions, regardless of the frequency they're
receiving, there are probably very few 'normal' radios or TV sets etc
where the LO runs below the tuned frequency.
--
Ian
M
micky
Guest
On Wed, 29 Oct 2014 09:30:32 -0000, "Arfa Daily"
<arfa.daily@ntlworld.com> wrote:
Oh, yeah. P... F... closely related (just add a curved line to the F.)
Thanks.
<arfa.daily@ntlworld.com> wrote:
snip
Well, I'm calling it weak because most radios won't get it, but Wikip
says that it's 50,000 watts ERF (sp?) but 88.1 is only 15,500 watts.
(also ERF? It didnt' say.)
ERP - Effective Radiated Power ?
Oh, yeah. P... F... closely related (just add a curved line to the F.)
The 'real' transmitter output multiplied
by the 'gain' of the transmitting antenna.
Thanks.
So maybe I'm calling it weak because it
farther away, in DC, not Baltimore where I live,
There are many many factors that affect the propagation of a VHF signal over
a lower frequency one, some of which will degrade that signal, and others of
which can, under the right conditions, enhance it. VHF signal reception is a
lottery, once you are outside the designed service area of the station.
but actually, there are
places north of here, farther from DC, the Westminster, Md. area, where
88.5 comes in well and 88.1 barely comes in. A friend moved to
Finksberg and she had to change to 88.5.
But maybe the FCC makes them arrange their antennas so that in the city
of Baltimore and its populous suburbs, 88.5 doesn't overpower 88.1.
But the frequencies are different, and there's no Baltimore 88.5, so why
would 88.5's antennas have to avoid the populous part of Baltimore, or
any part?
Without seeing a published map of the station's service area, it's
impossible to say. However, something as simple as a tall building in the
direction of the transmitting site, can be enough to cast a 'radio shadow'
across a large swathe of territory on the 'downstream' side
Arfa
Michael
M
micky
Guest
On Wed, 29 Oct 2014 14:01:57 -0500, amdx <nojunk@knology.net> wrote:
Not surprising. The Hip Hop people are a bunch of trouble-makers.
From the miscellaneous drawer, that same expensive KLM radio that gets
88.5 well all the way from DC got 88.1 well too, not surprising since
it's a Baltmore station and that's where I am.
But about 6 months ago, there started to quite a bit of static (FM
static? Maybe I should listen to it again. Anyhow, it was hard to
listen to.) on the local station on the expensive radio. But all**
the other much cheaper radios continue to get the local station just
fine. So sometimes it pays to be cheap.
** I keep buying radios from the 60's and 70's at hamfests, looking for
one that will get 88.1, 88.5 and 101.1
> Today I can't even find a semi local 94.3 MHz station.
LOL
On 10/29/2014 1:11 AM, micky wrote:
On Tue, 28 Oct 2014 16:39:16 -0400, Michael Black <et472@ncf.ca> wrote:
On Tue, 28 Oct 2014, Paul Drahn wrote:
On 10/27/2014 9:32 AM, micky wrote:
How can the same FM station appear at two different spots on the dial?
To the person who complained recently that I was off topic, I'm sorry.
This is not about any repair it would be feasible to make. It's only
about electronics.
Where I live there are two FM radio stations, 88.1 which is only a few
miles away, and 88.5 which is 40 or 50 miles away.
Right now, only my expensive KLM radio plus any car radio gets the
second one well, but I've had some cheap radios that do almost as well.
I lose track of which radios those are, so I'll start tuning at 88.1 and
tune up very gradually. After a period of silence, when I get above
88.5 to what I'd estimate is 88.6 or .7 or .8 I get 88.1 again.
How is that happening? I know about harmonics, but that doesn't apply,
does it?
P.S. This means 88.5 doesn't come in at all. I've tried stretching
out the power cord, which on the cheap radios is usually the antenna.
Sometimes that helps but on most of the radios, 88.5 won't come in at
all.
P.P.S. 88.1 is WYPR Baltimore. 88.5 is WAMU in DC. Sometimes they
play the same thing, like during the top of the hour news, Diane Rehm,
etc. although WAMU is on a 5 or 10 second delay most of the time.
Because the topic and the voices can be the same it means I can't tell
for a while if I've gotten 88.5 or just another 'instance' of 88.1.
If you have the AFC on, the station will pop up at different dial locations
depending on which direction you are tuning. At least my old portable does.
I think I've noticed this too.
But the AFC wasn't on, because that would have made it almost impossible
to get a weak station like 88.5.
Well, I'm calling it weak because most radios won't get it, but Wikip
says that it's 50,000 watts ERF (sp?) but 88.1 is only 15,500 watts.
(also ERF? It didnt' say.) So maybe I'm calling it weak because it
farther away, in DC, not Baltimore where I live, but actually, there are
places north of here, farther from DC, the Westminster, Md. area, where
88.5 comes in well and 88.1 barely comes in. A friend moved to
Finksberg and she had to change to 88.5.
But maybe the FCC makes them arrange their antennas so that in the city
of Baltimore and its populous suburbs, 88.5 doesn't overpower 88.1.
But the frequencies are different, and there's no Baltimore 88.5, so why
would 88.5's antennas have to avoid the populous part of Baltimore, or
any part?
I had a local situation at 94.5MHz interfering with 94.3MHz. The
94.3MHz station is an out of town station and signal strength is weaker.
The interference was on all my radios. I called the Radio station
engineer and he suggested the engineer from the out of town station
probably put me up to making the call, this was not true. From the
conversation, I think he had got a lot of calls about the interference,
but he assured my the station was in compliance with FCC Reg's. It was
Hip Hop vs O'Reilly back then. It went on that way for years until the
station changed from Hip Hop to some other format, then the interference
went away.
Not surprising. The Hip Hop people are a bunch of trouble-makers.
From the miscellaneous drawer, that same expensive KLM radio that gets
88.5 well all the way from DC got 88.1 well too, not surprising since
it's a Baltmore station and that's where I am.
But about 6 months ago, there started to quite a bit of static (FM
static? Maybe I should listen to it again. Anyhow, it was hard to
listen to.) on the local station on the expensive radio. But all**
the other much cheaper radios continue to get the local station just
fine. So sometimes it pays to be cheap.
** I keep buying radios from the 60's and 70's at hamfests, looking for
one that will get 88.1, 88.5 and 101.1
> Today I can't even find a semi local 94.3 MHz station.
LOL
Mikek
M
micky
Guest
On Wed, 29 Oct 2014 22:09:28 -0400, micky <NONONOmisc07@bigfoot.com>
wrote:
Not 101.1. 90.1, C-Span radio, which I guess I've lost interest in.
It's boring as all get out during the committee hearings, and the 7AM
program used to be great, but it's been discovered by the wackos.
Weekends, especailly evenings and nights, can be great. BookTV very
good. It or they had a long series about every president and another
series about every first lady, and their playing of the LBJ tapes was
enlightening (I'd wondered for decades if he really was pro-civil
rights or if his votes as senator were the real LBJ. It was the
first.)
wrote:
** I keep buying radios from the 60's and 70's at hamfests, looking for
one that will get 88.1, 88.5 and 101.1
Not 101.1. 90.1, C-Span radio, which I guess I've lost interest in.
It's boring as all get out during the committee hearings, and the 7AM
program used to be great, but it's been discovered by the wackos.
Weekends, especailly evenings and nights, can be great. BookTV very
good. It or they had a long series about every president and another
series about every first lady, and their playing of the LBJ tapes was
enlightening (I'd wondered for decades if he really was pro-civil
rights or if his votes as senator were the real LBJ. It was the
first.)
J
josephkk
Guest
On Wed, 29 Oct 2014 12:28:16 -0700, "William Sommerwerck"
<grizzledgeezer@comcast.net> wrote:
Nonsense, it would just change their location. Right into the VHF low TV
broadcast band (at least in the US).
?-)
<grizzledgeezer@comcast.net> wrote:
"Ian Jackson" wrote in message news:0iUda0GN0QUUFwOM@g3ohx.demon.co.uk...
I'm pretty sure that the local oscillator nearly always runs 10.7MHz
HIGHER than the radio signal.
Precisely If it were lower, you'd greatly increase the possibility of images.
Nonsense, it would just change their location. Right into the VHF low TV
broadcast band (at least in the US).
?-)
P
Phil Allison
Guest
Ian Jackson wrote:
** A man who prefers his ignorant opinions to facts is a complete fool:
The 6AQ8 along with the 12AT7 were the most common tubes used for LOs in FM tuners from the early 1950s onwards.
http://www.r-type.org/exhib/aav0008.htm
They were invariably used as low side oscillators.
Were not several TV channels tucked right under the FM band back then ?
All FM tuners have "image rejection" and benefit from "capture effect".
The former ranges from -40dB to -80dB while the latter ranges from 1 to 3dB.
So any image signal would be at least 100 to 10,000 times weaker than a good signal on the FM band - and it took only a 40% amplitude difference to make the stronger signal *completely* swamp the FM discriminator.
..... Phil
You don't change the mechanism for the interference, but because the two
TV channel allocations are where they are, if either was used in your
area you would certainly increase the possibility of interference from
them. However, as I've said, I think it's unusual for the LO to be on
the low side (probably for exactly this reason).
** A man who prefers his ignorant opinions to facts is a complete fool:
The 6AQ8 along with the 12AT7 were the most common tubes used for LOs in FM tuners from the early 1950s onwards.
http://www.r-type.org/exhib/aav0008.htm
They were invariably used as low side oscillators.
Were not several TV channels tucked right under the FM band back then ?
All FM tuners have "image rejection" and benefit from "capture effect".
The former ranges from -40dB to -80dB while the latter ranges from 1 to 3dB.
So any image signal would be at least 100 to 10,000 times weaker than a good signal on the FM band - and it took only a 40% amplitude difference to make the stronger signal *completely* swamp the FM discriminator.
..... Phil
I
Ian Jackson
Guest
In message <7ei35ads3e3n7bhuoqm1og396pe9pvslp4@4ax.com>, josephkk
<joseph_barrett@sbcglobal.net> writes
TV channel allocations are where they are, if either was used in your
area you would certainly increase the possibility of interference from
them. However, as I've said, I think it's unusual for the LO to be on
the low side (probably for exactly this reason).
--
Ian
<joseph_barrett@sbcglobal.net> writes
You don't change the mechanism for the interference, but because the twoOn Wed, 29 Oct 2014 12:28:16 -0700, "William Sommerwerck"
grizzledgeezer@comcast.net> wrote:
"Ian Jackson" wrote in message news:0iUda0GN0QUUFwOM@g3ohx.demon.co.uk...
I'm pretty sure that the local oscillator nearly always runs 10.7MHz
HIGHER than the radio signal.
Precisely If it were lower, you'd greatly increase the possibility of images.
Nonsense, it would just change their location. Right into the VHF low TV
broadcast band (at least in the US).
?-)
TV channel allocations are where they are, if either was used in your
area you would certainly increase the possibility of interference from
them. However, as I've said, I think it's unusual for the LO to be on
the low side (probably for exactly this reason).
--
Ian
M
Michael A. Terrell
Guest
amdx wrote:
Adjacent channel interference like that is caused by the IF bandwidth
and the skirt. The IF transformers aren't brick wall, the amplitude
drops away slowly outside the desired bandwidth. That allows a local
station to be strong enough to cause problems. AFC can make it worse, by
pulling the L.O. towards the stronger station.
--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
I had a local situation at 94.5MHz interfering with 94.3MHz. The
94.3MHz station is an out of town station and signal strength is weaker.
The interference was on all my radios. I called the Radio station
engineer and he suggested the engineer from the out of town station
probably put me up to making the call, this was not true. From the
conversation, I think he had got a lot of calls about the interference,
but he assured my the station was in compliance with FCC Reg's. It was
Hip Hop vs O'Reilly back then. It went on that way for years until the
station changed from Hip Hop to some other format, then the interference
went away.
Today I can't even find a semi local 94.3 MHz station.
Adjacent channel interference like that is caused by the IF bandwidth
and the skirt. The IF transformers aren't brick wall, the amplitude
drops away slowly outside the desired bandwidth. That allows a local
station to be strong enough to cause problems. AFC can make it worse, by
pulling the L.O. towards the stronger station.
--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
I
Ian Jackson
Guest
In message <035d039d-5d91-45ad-98db-bf81a53d2d88@googlegroups.com>, Phil
Allison <pallison49@gmail.com> writes
The fact that some what might now be considered 'highly desirable
collectibles' had low-side LOs doesn't mean it became a standard.
Not the present FM band. However, in the USA FM started life between 42
to 50MHz* but this was essentially experimental. After the war, it was
allocated the present band (87.8â107.9 MHz).
*Now the analogue TV IF range - which otherwise would have been Channel
1 - and hence TV starts at Channel 2.
through on 97.3MHz (at least on my kitchen radio)!
--
Ian
Allison <pallison49@gmail.com> writes
Ian Jackson wrote:
You don't change the mechanism for the interference, but because the two
TV channel allocations are where they are, if either was used in your
area you would certainly increase the possibility of interference from
them. However, as I've said, I think it's unusual for the LO to be on
the low side (probably for exactly this reason).
** A man who prefers his ignorant opinions to facts is a complete fool:
The 6AQ8 along with the 12AT7 were the most common tubes used for LOs
in FM tuners from the early 1950s onwards.
http://www.r-type.org/exhib/aav0008.htm
They were invariably used as low side oscillators.
The fact that some what might now be considered 'highly desirable
collectibles' had low-side LOs doesn't mean it became a standard.
Were not several TV channels tucked right under the FM band back then ?
Not the present FM band. However, in the USA FM started life between 42
to 50MHz* but this was essentially experimental. After the war, it was
allocated the present band (87.8â107.9 MHz).
*Now the analogue TV IF range - which otherwise would have been Channel
1 - and hence TV starts at Channel 2.
But that doesn't stop London Heathrow ATC (AM, of course) breakingAll FM tuners have "image rejection" and benefit from "capture effect".
The former ranges from -40dB to -80dB while the latter ranges from 1 to 3dB.
So any image signal would be at least 100 to 10,000 times weaker than a
good signal on the FM band - and it took only a 40% amplitude
difference to make the stronger signal *completely* swamp the FM
discriminator.
through on 97.3MHz (at least on my kitchen radio)!
--
Ian
W
William Sommerwerck
Guest
"micky" wrote in message news:fq435a9mkm4cv1lni8578gpekgtl93pn4r@4ax.com...
I assume you mean KLH. KLM is an airline.
Sammy Davis Jr once did a print ad for KLH in which he said "I used to think
KLH was an airline".
From the miscellaneous drawer, that same expensive KLM radio
that gets 88.5 well all the way from DC got 88.1 well too, not
surprising since it's a Baltmore station and that's where I am.
I assume you mean KLH. KLM is an airline.
Sammy Davis Jr once did a print ad for KLH in which he said "I used to think
KLH was an airline".
W
William Sommerwerck
Guest
"Phil Allison" wrote in message
news:1e547992-e524-4256-ae8a-ce0d67815bc8@googlegroups.com...
William Sommerwerck wrote:
Did you actually read what I wrote? The second sentence says that.
In the third sentence, I said "If the LO were //below// the incoming
signal..."
Do the math: 88.1 minus 10.7 plus 21.4 equals... what? 98.8?
I wasn't the one who brought up the point about having the LO below the
incoming frequency.
news:1e547992-e524-4256-ae8a-ce0d67815bc8@googlegroups.com...
William Sommerwerck wrote:
Given that the FM band is 20MHz, and twice 10.7 MHz is greater than 20MHz,
if
the LO is above the incoming signal, images would come from stations above
107.9MHz (outside the band).
If the LO were below the incoming signal, you could have in-band images
starting at 98.9MHz.
** Nonsense.
Long as a particular band has less width than double the IF frequency,
no in-band images will occur.
Did you actually read what I wrote? The second sentence says that.
In the third sentence, I said "If the LO were //below// the incoming
signal..."
Do the math: 88.1 minus 10.7 plus 21.4 equals... what? 98.8?
I wasn't the one who brought up the point about having the LO below the
incoming frequency.
W
William Sommerwerck
Guest
"Phil Allison" wrote in message
news:035d039d-5d91-45ad-98db-bf81a53d2d88@googlegroups.com...
Fascinating. I never knew this.
news:035d039d-5d91-45ad-98db-bf81a53d2d88@googlegroups.com...
The 6AQ8 along with the 12AT7 were the most common tubes used for LOs
in FM tuners from the early 1950s onwards.
http://www.r-type.org/exhib/aav0008.htm
They were invariably used as low-side oscillators.
Fascinating. I never knew this.
A
amdx
Guest
On 10/29/2014 9:09 PM, micky wrote:
station at 94.3 playing O'Reilly while their programing had Limbaugh on.
Tried my truck radio today, I got 94.3MHz, JOY FM a religious
station. Covers the AL./FL. line near Dothan. Poor signal though.
Mikek
The station is part of a group, and their 94.5 was interfering with aOn Wed, 29 Oct 2014 14:01:57 -0500, amdx <nojunk@knology.net> wrote:
On 10/29/2014 1:11 AM, micky wrote:
On Tue, 28 Oct 2014 16:39:16 -0400, Michael Black <et472@ncf.ca> wrote:
On Tue, 28 Oct 2014, Paul Drahn wrote:
On 10/27/2014 9:32 AM, micky wrote:
How can the same FM station appear at two different spots on the dial?
To the person who complained recently that I was off topic, I'm sorry.
This is not about any repair it would be feasible to make. It's only
about electronics.
Where I live there are two FM radio stations, 88.1 which is only a few
miles away, and 88.5 which is 40 or 50 miles away.
Right now, only my expensive KLM radio plus any car radio gets the
second one well, but I've had some cheap radios that do almost as well.
I lose track of which radios those are, so I'll start tuning at 88.1 and
tune up very gradually. After a period of silence, when I get above
88.5 to what I'd estimate is 88.6 or .7 or .8 I get 88.1 again.
How is that happening? I know about harmonics, but that doesn't apply,
does it?
P.S. This means 88.5 doesn't come in at all. I've tried stretching
out the power cord, which on the cheap radios is usually the antenna.
Sometimes that helps but on most of the radios, 88.5 won't come in at
all.
P.P.S. 88.1 is WYPR Baltimore. 88.5 is WAMU in DC. Sometimes they
play the same thing, like during the top of the hour news, Diane Rehm,
etc. although WAMU is on a 5 or 10 second delay most of the time.
Because the topic and the voices can be the same it means I can't tell
for a while if I've gotten 88.5 or just another 'instance' of 88.1.
If you have the AFC on, the station will pop up at different dial locations
depending on which direction you are tuning. At least my old portable does.
I think I've noticed this too.
But the AFC wasn't on, because that would have made it almost impossible
to get a weak station like 88.5.
Well, I'm calling it weak because most radios won't get it, but Wikip
says that it's 50,000 watts ERF (sp?) but 88.1 is only 15,500 watts.
(also ERF? It didnt' say.) So maybe I'm calling it weak because it
farther away, in DC, not Baltimore where I live, but actually, there are
places north of here, farther from DC, the Westminster, Md. area, where
88.5 comes in well and 88.1 barely comes in. A friend moved to
Finksberg and she had to change to 88.5.
But maybe the FCC makes them arrange their antennas so that in the city
of Baltimore and its populous suburbs, 88.5 doesn't overpower 88.1.
But the frequencies are different, and there's no Baltimore 88.5, so why
would 88.5's antennas have to avoid the populous part of Baltimore, or
any part?
I had a local situation at 94.5MHz interfering with 94.3MHz. The
94.3MHz station is an out of town station and signal strength is weaker.
The interference was on all my radios. I called the Radio station
engineer and he suggested the engineer from the out of town station
probably put me up to making the call, this was not true. From the
conversation, I think he had got a lot of calls about the interference,
but he assured my the station was in compliance with FCC Reg's. It was
Hip Hop vs O'Reilly back then. It went on that way for years until the
station changed from Hip Hop to some other format, then the interference
went away.
Not surprising. The Hip Hop people are a bunch of trouble-makers.
station at 94.3 playing O'Reilly while their programing had Limbaugh on.
From the miscellaneous drawer, that same expensive KLM radio that gets
88.5 well all the way from DC got 88.1 well too, not surprising since
it's a Baltmore station and that's where I am.
But about 6 months ago, there started to quite a bit of static (FM
static? Maybe I should listen to it again. Anyhow, it was hard to
listen to.) on the local station on the expensive radio. But all**
the other much cheaper radios continue to get the local station just
fine. So sometimes it pays to be cheap.
** I keep buying radios from the 60's and 70's at hamfests, looking for
one that will get 88.1, 88.5 and 101.1
Today I can't even find a semi local 94.3 MHz station.
LOL
Tried my truck radio today, I got 94.3MHz, JOY FM a religious
station. Covers the AL./FL. line near Dothan. Poor signal though.
Mikek
D
David Platt
Guest
I had a local situation at 94.5MHz interfering with 94.3MHz. The
94.3MHz station is an out of town station and signal strength is weaker.
The interference was on all my radios. I called the Radio station
engineer and he suggested the engineer from the out of town station
probably put me up to making the call, this was not true. From the
conversation, I think he had got a lot of calls about the interference,
but he assured my the station was in compliance with FCC Reg's. It was
Hip Hop vs O'Reilly back then. It went on that way for years until the
station changed from Hip Hop to some other format, then the interference
went away.
The station engineer might have been telling the strict truth... it
would have taken a spectrum analyzer or modulation meter to be sure.
Commercial FM is generally allowed a +/- 75 kHz carrier deviation.
Due to the way FM works, and due to the fact that the station is
transmitting a stereo subcarrier (centered on 38 kHz, with its own
sidebands going out as much as 15 kHz on either side), the FM
station's actual RF "footprint" can easily have significant energy 120
kHz on either side of its nominal carrier frequency. That's more than
half-way out to the "alternate" channel center, 200 kHz away. If the
station tends to run "loud" (highly compressed audio, cranked all the
way up) then the "wide footprint" is likely to be present much or most
of the time.
Things can be even worse these days, since many stations are also
transmitting in-band/on-channel digital subcarriers which go out even
further.
A lot of FM radios/receivers have fairly "broad" intermediate-
frequency filters... e.g. one or two crystal filters with 220 kHz or
even 250 kHz bandwidth. Such broad receptivity lets almost all of the
"desired" station's signal in... and that's good for low-distortion
stereo reception since you get the whole stereo subcarrier.
Unfortunately, if there's a strong signal on the "alternate" channel
(200 kHz away), that signal's outer sidebands will end up getting
through the filter, and will probably affect the stereo subcarrier and
increase distortion or "break through" into audibility. If you're
trying to tune in a weak, distant signal that's on an "adjacent"
channel to a strong local (100 kHz away) the problem is even worse.
There are ways to work around this:
- Use an FM tuner which has a narrower IF bandwidth. Better tuners
often have a wide/narrow switch setting, with the narrow setting
using different (or more) crystal filters with reduced bandwidth -
200, 180, 150, or even 110 kHz.
The narrower filters can eliminate a lot of adjacent- and
alternate-channel bleedover. The price is higher distortion
(especially in stereo) since the outer FM sidebands of the desired
station are also eliminated by the narrower filters.
- Use a directional FM antenna, and aim it in the direction which
gives the best results. This may be "aimed towards the desired
station" (increasing its relative strength), or "aimed at an angle
away from the undesired station" (to put the interfering station in
a "null" in the antenna's reception pattern).