We have a system in place in the local area whereby the fire
departments monitor fire alarm signals at the fire stations in most of
the area towns. It is mandatory that all businesses as well as
commercial properties are equipped with fire alarm systems. Two of the
most common methods of communicating with these fire departments is
either by master box telegraph which sends a coded signal by operating
a wind up eccentric interrupter via municipal overhead wire, or by
radio transmitters which are connected to these fire alarm systems.

With the radio system, in the event of a fire, three short bursts of
data are sent over approximately a one second period. The location,
event, and zone information are all sent during this period. The
maximum allowable power output is one watt The signal is AM at a
frequency of 72MHZ. The terrain is hilly. Most transmitting antennas
are omni directional affairs which seem to work adequately however
there are some cases where it is necessary to use a directional
antenna.

It should also be noted that most fire departments have more than one
receiver with antennas located in different locations. Sometimes these
antennas are miles apart. Depending on topography, it is sometimes not
possible for a transmitter to hit one receiver, however it may hit the
other with a good signal. Redundancy is important but most fire
departments understand propagation somewhat and are satisfied with a
good signal at one receiving location.

We have one transmitter location which is about 5 miles from the fire
station. The terrain is somewhat hilly however not pronounced. The
fire station has two receivers with both antennas that were installed
on the roof about ten feet apart. This makes no sense to me. It seems
like they should have been put in two different locations as other
towns do it to be able to receive signals coming from other locations
which may be blocked to the other antenna.

In this instance, these two receiving antennas and the transmitter
location form a straight line. This particular fire department is
insisting on reception on both its receivers. The complaint is that
the fire department is receiving a good signal on one of its receivers
but not the other one.

We have tried moving the antenna to another part of the building,
raising it 25 feet, and replacing the RG 58U cable with RG 213.
Nothing seems to work. I've also considered using a Yagi however It
has been suggested to me that in this case perhaps the second
receiving antenna may be blocked by the first, which has created a
dead spot to this particular transmitter location.

In my opinion, this two antennas in the same location arrangement also
eliminates any advantage the fire department would realize of
receiving any signals from a blocked transmitting location. I'm also
wondering if two receiving antennas operating on the same frequency
should have been installed that close together in the first place.

Does anyone have any suggestions The fire inspector knows little
about radio and is a real pain in the ass. Thanks, Lenny.

Perhaps a polarization change would help.
Sometimes as radio signals get reflected/refracted they can swing 90degree
pol.

Perhaps try mounting the Tx or one of the Rx antennas horizontally as a
test?


P
wrote in message
...
We have a system in place in the local area whereby the fire
departments monitor fire alarm signals at the fire stations in most of
the area towns. It is mandatory that all businesses as well as
commercial properties are equipped with fire alarm systems. Two of the
most common methods of communicating with these fire departments is
either by master box telegraph which sends a coded signal by operating
a wind up eccentric interrupter via municipal overhead wire, or by
radio transmitters which are connected to these fire alarm systems.

With the radio system, in the event of a fire, three short bursts of
data are sent over approximately a one second period. The location,
event, and zone information are all sent during this period. The
maximum allowable power output is one watt The signal is AM at a
frequency of 72MHZ. The terrain is hilly. Most transmitting antennas
are omni directional affairs which seem to work adequately however
there are some cases where it is necessary to use a directional
antenna.

It should also be noted that most fire departments have more than one
receiver with antennas located in different locations. Sometimes these
antennas are miles apart. Depending on topography, it is sometimes not
possible for a transmitter to hit one receiver, however it may hit the
other with a good signal. Redundancy is important but most fire
departments understand propagation somewhat and are satisfied with a
good signal at one receiving location.

We have one transmitter location which is about 5 miles from the fire
station. The terrain is somewhat hilly however not pronounced. The
fire station has two receivers with both antennas that were installed
on the roof about ten feet apart. This makes no sense to me. It seems
like they should have been put in two different locations as other
towns do it to be able to receive signals coming from other locations
which may be blocked to the other antenna.

In this instance, these two receiving antennas and the transmitter
location form a straight line. This particular fire department is
insisting on reception on both its receivers. The complaint is that
the fire department is receiving a good signal on one of its receivers
but not the other one.

We have tried moving the antenna to another part of the building,
raising it 25 feet, and replacing the RG 58U cable with RG 213.
Nothing seems to work. I've also considered using a Yagi however It
has been suggested to me that in this case perhaps the second
receiving antenna may be blocked by the first, which has created a
dead spot to this particular transmitter location.

In my opinion, this two antennas in the same location arrangement also
eliminates any advantage the fire department would realize of
receiving any signals from a blocked transmitting location. I'm also
wondering if two receiving antennas operating on the same frequency
should have been installed that close together in the first place.

Does anyone have any suggestions The fire inspector knows little
about radio and is a real pain in the ass. Thanks, Lenny.



--- news://freenews.netfront.net/ - complaints: ---

wrote:

We have a system in place in the local area whereby the fire
departments monitor fire alarm signals at the fire stations in most of
the area towns. It is mandatory that all businesses as well as
commercial properties are equipped with fire alarm systems. Two of the
most common methods of communicating with these fire departments is
either by master box telegraph which sends a coded signal by operating
a wind up eccentric interrupter via municipal overhead wire, or by
radio transmitters which are connected to these fire alarm systems.

With the radio system, in the event of a fire, three short bursts of
data are sent over approximately a one second period. The location,
event, and zone information are all sent during this period. The
maximum allowable power output is one watt The signal is AM at a
frequency of 72MHZ. The terrain is hilly. Most transmitting antennas
are omni directional affairs which seem to work adequately however
there are some cases where it is necessary to use a directional
antenna.

It should also be noted that most fire departments have more than one
receiver with antennas located in different locations. Sometimes these
antennas are miles apart. Depending on topography, it is sometimes not
possible for a transmitter to hit one receiver, however it may hit the
other with a good signal. Redundancy is important but most fire
departments understand propagation somewhat and are satisfied with a
good signal at one receiving location.

We have one transmitter location which is about 5 miles from the fire
station. The terrain is somewhat hilly however not pronounced. The
fire station has two receivers with both antennas that were installed
on the roof about ten feet apart. This makes no sense to me. It seems
like they should have been put in two different locations as other
towns do it to be able to receive signals coming from other locations
which may be blocked to the other antenna.

In this instance, these two receiving antennas and the transmitter
location form a straight line. This particular fire department is
insisting on reception on both its receivers. The complaint is that
the fire department is receiving a good signal on one of its receivers
but not the other one.

We have tried moving the antenna to another part of the building,
raising it 25 feet, and replacing the RG 58U cable with RG 213.
Nothing seems to work. I've also considered using a Yagi however It
has been suggested to me that in this case perhaps the second
receiving antenna may be blocked by the first, which has created a
dead spot to this particular transmitter location.

In my opinion, this two antennas in the same location arrangement also
eliminates any advantage the fire department would realize of
receiving any signals from a blocked transmitting location. I'm also
wondering if two receiving antennas operating on the same frequency
should have been installed that close together in the first place.

Does anyone have any suggestions The fire inspector knows little
about radio and is a real pain in the ass. Thanks, Lenny.
I would put a signal ref on the input of the question receiver. If both
are on the same frequency with separate antennas of the same type I
assume, there is something wrong!

This also assumes that both receivers are of the same model..

It makes me think that maybe the front end of the question receiver
is weak or, passing through a narrow filter which is not tuned correctly.

Have you tried switching the feeds at the receivers to see if the
bad receiver becomes good?



--
"I'd rather have a bottle in front of me than a frontal lobotomy"

"Daily Thought:

SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
http://webpages.charter.net/jamie_5"

Jamie Inscribed thus:

wrote:

We have a system in place in the local area whereby the fire
departments monitor fire alarm signals at the fire stations in most
of the area towns. It is mandatory that all businesses as well as
commercial properties are equipped with fire alarm systems. Two of
the most common methods of communicating with these fire departments
is either by master box telegraph which sends a coded signal by
operating a wind up eccentric interrupter via municipal overhead
wire, or by radio transmitters which are connected to these fire
alarm systems.

With the radio system, in the event of a fire, three short bursts of
data are sent over approximately a one second period. The location,
event, and zone information are all sent during this period. The
maximum allowable power output is one watt The signal is AM at a
frequency of 72MHZ. The terrain is hilly. Most transmitting antennas
are omni directional affairs which seem to work adequately however
there are some cases where it is necessary to use a directional
antenna.

It should also be noted that most fire departments have more than one
receiver with antennas located in different locations. Sometimes
these antennas are miles apart. Depending on topography, it is
sometimes not possible for a transmitter to hit one receiver, however
it may hit the other with a good signal. Redundancy is important but
most fire departments understand propagation somewhat and are
satisfied with a good signal at one receiving location.

We have one transmitter location which is about 5 miles from the fire
station. The terrain is somewhat hilly however not pronounced. The
fire station has two receivers with both antennas that were installed
on the roof about ten feet apart. This makes no sense to me. It seems
like they should have been put in two different locations as other
towns do it to be able to receive signals coming from other locations
which may be blocked to the other antenna.

In this instance, these two receiving antennas and the transmitter
location form a straight line. This particular fire department is
insisting on reception on both its receivers. The complaint is that
the fire department is receiving a good signal on one of its
receivers but not the other one.

We have tried moving the antenna to another part of the building,
raising it 25 feet, and replacing the RG 58U cable with RG 213.
Nothing seems to work. I've also considered using a Yagi however It
has been suggested to me that in this case perhaps the second
receiving antenna may be blocked by the first, which has created a
dead spot to this particular transmitter location.

In my opinion, this two antennas in the same location arrangement
also eliminates any advantage the fire department would realize of
receiving any signals from a blocked transmitting location. I'm also
wondering if two receiving antennas operating on the same frequency
should have been installed that close together in the first place.

Does anyone have any suggestions The fire inspector knows little
about radio and is a real pain in the ass. Thanks, Lenny.
I would put a signal ref on the input of the question receiver. If
both are on the same frequency with separate antennas of the same type
I assume, there is something wrong!

This also assumes that both receivers are of the same model..

It makes me think that maybe the front end of the question receiver
is weak or, passing through a narrow filter which is not tuned
correctly.

Have you tried switching the feeds at the receivers to see if the
bad receiver becomes good?


Switching feeds would be the common sense thing to do first ! One
receiver could have a bad front end.

--
Best Regards:
Baron.

" wrote:

We have a system in place in the local area whereby the fire
departments monitor fire alarm signals at the fire stations in most of
the area towns. It is mandatory that all businesses as well as
commercial properties are equipped with fire alarm systems. Two of the
most common methods of communicating with these fire departments is
either by master box telegraph which sends a coded signal by operating
a wind up eccentric interrupter via municipal overhead wire, or by
radio transmitters which are connected to these fire alarm systems.

With the radio system, in the event of a fire, three short bursts of
data are sent over approximately a one second period. The location,
event, and zone information are all sent during this period. The
maximum allowable power output is one watt The signal is AM at a
frequency of 72MHZ. The terrain is hilly. Most transmitting antennas
are omni directional affairs which seem to work adequately however
there are some cases where it is necessary to use a directional
antenna.

It should also be noted that most fire departments have more than one
receiver with antennas located in different locations.


Receiver voting: it allows the selection of the strongest received
signal from multiple sites.

http://www.google.com/search?hl=en&safe=off&client=firefox-a&rls=org.mozilla:en-USfficial&hs=l7E&num=100&newwindow=1&ei=PgBdS7jd Do6H8Qbv3OT3BA&sa=X&oi=spell&resnum=0&ct=result&cd =1&ved=0CAYQBSgA&q=receiver+voting&spell=1


Sometimes these
antennas are miles apart. Depending on topography, it is sometimes not
possible for a transmitter to hit one receiver, however it may hit the
other with a good signal. Redundancy is important but most fire
departments understand propagation somewhat and are satisfied with a
good signal at one receiving location.

We have one transmitter location which is about 5 miles from the fire
station. The terrain is somewhat hilly however not pronounced. The
fire station has two receivers with both antennas that were installed
on the roof about ten feet apart. This makes no sense to me. It seems
like they should have been put in two different locations as other
towns do it to be able to receive signals coming from other locations
which may be blocked to the other antenna.

In this instance, these two receiving antennas and the transmitter
location form a straight line. This particular fire department is
insisting on reception on both its receivers. The complaint is that
the fire department is receiving a good signal on one of its receivers
but not the other one.

We have tried moving the antenna to another part of the building,
raising it 25 feet, and replacing the RG 58U cable with RG 213.
Nothing seems to work. I've also considered using a Yagi however It
has been suggested to me that in this case perhaps the second
receiving antenna may be blocked by the first, which has created a
dead spot to this particular transmitter location.

In my opinion, this two antennas in the same location arrangement also
eliminates any advantage the fire department would realize of
receiving any signals from a blocked transmitting location. I'm also
wondering if two receiving antennas operating on the same frequency
should have been installed that close together in the first place.


Two antenna used for receiving shouldn't affect each other. Do you
have a TV field strength meter available? You should be able to compare
the signals from both antennas. A 50 to 74 ohm adapter will give a
better match, but the resistive type will introduce a 6 dB loss. One can
be made from one of the six hole ferrite beads. Wind the wire through
all six holes, and a tap at the fifth turn. The tap is 50 ohms, and the
sixth turn is 72 ohms.


Does anyone have any suggestions The fire inspector knows little
about radio and is a real pain in the ass. Thanks, Lenny.


Is there a local ham radio club? You might find a member who builds
and maintains a repeater system who could help.


--
Greed is the root of all eBay.

"Michael A. Terrell"

Two antenna used for receiving shouldn't affect each other. Do you
have a TV field strength meter available? You should be able to compare
the signals from both antennas.



** What signals ?

Certainly NOT very brief, very weak data bursts on 72 MHz narrowband AM.

Only if there is a VHF channel 4 TV transmitter in the vicinity, could the
meter be of any use.


..... Phil

On Jan 24, 6:56*pm, "Phil Allison" wrote:
"Michael A. Terrell"



Two antenna used for receiving shouldn't affect each other. *Do you
have a TV field strength meter available? *You should be able to compare
the signals from both antennas.

** What signals ?

Certainly *NOT very brief, very weak data bursts on 72 MHz narrowband AM.

Only if there is a VHF channel 4 TV transmitter in the vicinity, could the
meter be of any use.

.... *Phil

FYI since the Digital TV analog shutdown last summer, there are no
channel 4s and 8 channel 5s in the country. Low band VHF is no longer
coveted real estate.

G²

wrote:

On Jan 24, 6:56 pm, "Phil Allison" wrote:
"Michael A. Terrell"



Two antenna used for receiving shouldn't affect each other. Do you
have a TV field strength meter available? You should be able to compare
the signals from both antennas.

** What signals ?

Certainly NOT very brief, very weak data bursts on 72 MHz narrowband AM.

Only if there is a VHF channel 4 TV transmitter in the vicinity, could the
meter be of any use.

.... Phil

FYI since the Digital TV analog shutdown last summer, there are no
channel 4s and 8 channel 5s in the country. Low band VHF is no longer
coveted real estate.


There are other signals, like FM broadcast that will be picked up by
the antennas that can be measured with a TV FSM. All you are looking
for is something to compare the two antenna systems.


--
Greed is the root of all eBay.

wrote in message
...
On Jan 24, 6:56 pm, "Phil Allison"
wrote:
"Michael A. Terrell"



Two antenna used for receiving shouldn't affect each
other. Do you
have a TV field strength meter available? You should
be able to compare
the signals from both antennas.

** What signals ?

Certainly NOT very brief, very weak data bursts on 72
MHz narrowband AM.

Only if there is a VHF channel 4 TV transmitter in the
vicinity, could the
meter be of any use.

.... Phil

FYI since the Digital TV analog shutdown last summer,
there are no
channel 4s and 8 channel 5s in the country. Low band VHF
is no longer
coveted real estate.

G²

Actually, Chicago has a digital signal on channel
4.(WOCK-CD). See:

http://en.wikipedia.org/wiki/WOCK-CD

David

On Jan 25, 6:28*am, "David" wrote:
wrote in message

...





On Jan 24, 6:56 pm, "Phil Allison"
wrote:
"Michael A. Terrell"

Two antenna used for receiving shouldn't affect each
other. *Do you
have a TV field strength meter available? *You should
be able to compare
the signals from both antennas.

** What signals ?

Certainly *NOT very brief, very weak data bursts on 72
MHz narrowband AM.

Only if there is a VHF channel 4 TV transmitter in the
vicinity, could the
meter be of any use.

.... *Phil

FYI since the Digital TV analog shutdown last summer,
there are no
channel 4s and 8 channel 5s in the country. Low band VHF
is no longer
coveted real estate.

G

Actually, Chicago has a digital signal on channel
4.(WOCK-CD). See:

http://en.wikipedia.org/wiki/WOCK-CD

David

When I made that statement I looked through this list

http://www.dtv.gov/stationlist.htm

I thought this list was part of the FCC. In any event they don't list
WOCK which appears to be a comparatively low power station. Suffice it
to say they are very few low band VHF stations operating in the US.

G²

wrote in message
...
On Jan 25, 6:28 am, "David" wrote:
wrote in message
snip
FYI since the Digital TV analog shutdown last summer,
there are no
channel 4s and 8 channel 5s in the country. Low band
VHF
is no longer
coveted real estate.

G

Actually, Chicago has a digital signal on channel
4.(WOCK-CD). See:

http://en.wikipedia.org/wiki/WOCK-CD

David

When I made that statement I looked through this list

http://www.dtv.gov/stationlist.htm

I thought this list was part of the FCC. In any event they
don't list
WOCK which appears to be a comparatively low power
station. Suffice it
to say they are very few low band VHF stations operating
in the US.

G²

I am 36 miles west from their transmitting site and also not
in the main lobe. I only noticed they were on the air when I
was wondering where some interference on my master antenna
was originating. I use a combination band stop - band pass
filter to insert an analog channel 4 into my antenna
distribution system which is used throughout the house to
serve several TV sets with ATSC tuners or digital
converters. I use analog channel 4 to send whatever is tuned
by a receiver connected to a pay TV service and controlled
by RF remotes. This arrangement has worked very well until
WOCK increased their power to 3KW. For digital on that
channel this is really not low power. Before the transition,
the local CBS station was on channel 3 for several years
with 4.4KW ERP. Retuning the filters more accurately
eliminated the problem and I really was not interested in
Korean programming anyhow. I suppose I could have moved the
analog channel somewhere else, but that would be a lot of
work.

David

On Sun, 24 Jan 2010 10:54:09 -0800 (PST),
" wrote:

The
fire station has two receivers with both antennas that were installed
on the roof about ten feet apart. This makes no sense to me.

Diversity receiver. It's much the same as with the common wireless
router that has two antennas. One antenna is considered the main
antenna, the other the auxillary antenna. The receiver sits on the
main antenna until it hears something. If the error rate is high on
what it's hearing, it switches to the aux antenna.

The idea is to eliminate frequency selective fading. That's where the
direct path and a reflected path both converge on an antenna, but due
to the differences in path length, may cancel or distort the received
signal. It's only necessary to move 1/2 wavelength in order to
eliminate this effect, which is what the aux antenna does.

There are pleny of other methods of accomplishing the same thing. For
example, redundant receivers, both listening to the same channel, and
comparing results are possible. Same with two receivers on different
RF frequencies, in order to accomidate congestion.

It seems
like they should have been put in two different locations as other
towns do it to be able to receive signals coming from other locations
which may be blocked to the other antenna.

See receiver voting systems. These are common in municipal
communications systems, where it is difficult to hear a handheld radio
at all points of the city. Mutliple receivers are used as you
describe. The hard part is deciding which receiver should be heard by
the dispatcher, which is what the voting system does.

In this instance, these two receiving antennas and the transmitter
location form a straight line. This particular fire department is
insisting on reception on both its receivers. The complaint is that
the fire department is receiving a good signal on one of its receivers
but not the other one.

Are you sure that there are two receivers and not one receiver and an
antenna switch? Some makers and model numbers would be useful. At
72Mhz, two closely spaced antennas should hear roughly the same thing.
If one doesn't, it's broken somewhere. What's not clear is whether
the signal is weak or just not there.

We have tried moving the antenna to another part of the building,
raising it 25 feet, and replacing the RG 58U cable with RG 213.
Nothing seems to work. I've also considered using a Yagi however

A 72Mhz Yagi is rather large and expensive.

It
has been suggested to me that in this case perhaps the second
receiving antenna may be blocked by the first, which has created a
dead spot to this particular transmitter location.

It's possible, but not likely. How far apart are the fire departments
two antennas spaced? Are they perhaps on opposite sides of a tower or
pole?

With careful construction, it's possible to create a cardioid pattern
with two omni antennas and a phaseing harness, but the beast is so
critical in construction, that it's unlikely to have been constructed
by accident. Similarly, if one antenna were acting as a reflector for
the other, the maximum gain or loss would be about 3dB, which should
not be noticable.

In my opinion, this two antennas in the same location arrangement also
eliminates any advantage the fire department would realize of
receiving any signals from a blocked transmitting location.

I doubt it but it's possible. If the antennas are side mounted on a
tower, the tower will do some blocking. Spacing of the antennas away
from the tower also have a big effect. There's a section in the ARRL
antenna handbook and other publications showing the effects to an
omnidirectional pattern caused by various antenna to tower spacing.

A photograph of the fire dept antenna structure would be helpful.

I'm also
wondering if two receiving antennas operating on the same frequency
should have been installed that close together in the first place.

It's not a problem.

Does anyone have any suggestions The fire inspector knows little
about radio and is a real pain in the ass. Thanks, Lenny.

Replace the sick receiver with a cheap scanner receiver and see if it
hears your transmissions. If it does, fix the receiver.

--
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 Jan 26, 2:41*pm, Jeff Liebermann wrote:
On Sun, 24 Jan 2010 10:54:09 -0800 (PST),

" wrote:
The
fire station has two receivers with both antennas that were installed
on the roof about ten feet apart. This makes no sense to me.

Diversity receiver. *It's much the same as with the common wireless
router that has two antennas. *One antenna is considered the main
antenna, the other the auxillary antenna. *The receiver sits on the
main antenna until it hears something. *If the error rate is high on
what it's hearing, it switches to the aux antenna. *

The idea is to eliminate frequency selective fading. *That's where the
direct path and a reflected path both converge on an antenna, but due
to the differences in path length, may cancel or distort the received
signal. *It's only necessary to move 1/2 wavelength in order to
eliminate this effect, which is what the aux antenna does.

There are pleny of other methods of accomplishing the same thing. *For
example, redundant receivers, both listening to the same channel, and
comparing results are possible. *Same with two receivers on different
RF frequencies, in order to accomidate congestion.

It seems
like they should have been put in two different locations as other
towns do it to be able to receive signals coming from other locations
which may be blocked to the other antenna.

See receiver voting systems. *These are common in municipal
communications systems, where it is difficult to hear a handheld radio
at all points of the city. *Mutliple receivers are used as you
describe. *The hard part is deciding which receiver should be heard by
the dispatcher, which is what the voting system does.

In this instance, these two receiving antennas and the transmitter
location form a straight line. This particular fire department is
insisting on reception on both its receivers. The complaint is that
the fire department is receiving a good signal on one of its receivers
but not the other one.

Are you sure that there are two receivers and not one receiver and an
antenna switch? *Some makers and model numbers would be useful. *At
72Mhz, two closely spaced antennas should hear roughly the same thing.
If one doesn't, it's broken somewhere. *What's not clear is whether
the signal is weak or just not there. *

We have tried moving the antenna to another part of the building,
raising it 25 feet, and replacing the RG 58U cable with RG 213.
Nothing seems to work. I've also considered using a Yagi however

A 72Mhz Yagi is rather large and expensive.

It
has been suggested to me that in this case perhaps the second
receiving antenna may be blocked by the first, which has created a
dead spot to this particular transmitter location.

It's possible, but not likely. *How far apart are the fire departments
two antennas spaced? *Are they perhaps on opposite sides of a tower or
pole?

With careful construction, it's possible to create a cardioid pattern
with two omni antennas and a phaseing harness, but the beast is so
critical in construction, that it's unlikely to have been constructed
by accident. *Similarly, if one antenna were acting as a reflector for
the other, the maximum gain or loss would be about 3dB, which should
not be noticable.

In my opinion, this two antennas in the same location arrangement also
eliminates any advantage the fire department would realize of
receiving any signals from a blocked transmitting location.

I doubt it but it's possible. *If the antennas are side mounted on a
tower, the tower will do some blocking. *Spacing of the antennas away
from the tower also have a big effect. *There's a section in the ARRL
antenna handbook and other publications showing the effects to an
omnidirectional pattern caused by various antenna to tower spacing.

A photograph of the fire dept antenna structure would be helpful. *

I'm also
wondering if two receiving antennas operating on the same frequency
should have been installed that close together in the first place.

It's not a problem.

Does anyone have any suggestions *The fire inspector knows little
about radio and is a real pain in the ass. Thanks, Lenny.

Replace the sick receiver with a cheap scanner receiver and see if it
hears your transmissions. *If it does, fix the receiver.

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

I'm told that the other receiver does pick up signals from other
transmitters using simple omni directional antennas in the same
general area as ours. The fire dept will not let us tamper with their
equipment so confirming a weak front end is not possible. Its an
almost impossible situation. While I might be able to place a scanner
down in the FD office and try to hear the signal, however it won't be
off the suspect receiving antenna. And even if I can hear a signal if
it doesn't come in on their receiver, it still is not going to make
them happy. We may have to get the receiver contractor involved. But
who's going to pay for that? How do I get these jobs anyway? Lenny

On Fri, 29 Jan 2010 07:06:56 -0800 (PST),
" wrote:

I'm told that the other receiver does pick up signals from other
transmitters using simple omni directional antennas in the same
general area as ours. The fire dept will not let us tamper with their
equipment so confirming a weak front end is not possible. Its an
almost impossible situation.

How does this prevent you from taking a photograph of the antenna
structure in order to answer my questions? Yes, the fire department
will not let you touch the hardware. However, you can identify the
probable cause by substitution (i.e. scanner and 3rd antenna) which
will surely attract the attention of their radio service contractor or
department.

While I might be able to place a scanner
down in the FD office and try to hear the signal, however it won't be
off the suspect receiving antenna.

That's fine. You can then say. It works with my equipment. It
doesn't work with your equipment. Your equipment is broken.

And even if I can hear a signal if
it doesn't come in on their receiver, it still is not going to make
them happy.

This is a technical newsgroup, not a political. We can identify and
solve technical problems. However, if you have a credibility problem
with the fire department, I suggest you obtain the assistance of
either a technically qualified communications engineer or tech. If
that is insufficient to make the fire department "happy", perhaps a
local politician might inspire cooperation.

We may have to get the receiver contractor involved.

Hint: The more people involved in YOUR problem, the more complicated
it will become. Find one person in your area that is familiar with
the equipment and let them do the necessary testing. If you call out
the troops, there will be plenty of activity and noise, but little
useful in the way of a solution.

But
who's going to pay for that?

You are. It's *YOUR* problem. As far as the fire department is
concerned, at this time, they're equipment works just fine. They can
also demonstrate it with tests from other users.

How do I get these jobs anyway? Lenny

Karma failure. Good deeds often help.


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