Don't know where you can buy a passband filter. Maybe be able to find some
cavity type filters for 50 MHz, but probably only surplus. Building from
scratch
is easy but takes a network analyzer to tune.

A coax stub can be either open or shorted, your preference. Cheapest way is
to
start with an open stub slightly too long and trim it to length. If you can
borrow
a signal generator and power meter, then you can tune it that way.

It's practical to get about 25 dB of loss with a stub, better is difficult
due to losses
in the conectors, cables, etc.

Rough length of the open stub would be 1/4 wavelength at 55.25 MHz, about
1.35 meters. Accounting for coax velocity factor of 0.66, the stub would be
about
0.89 meters long. Start a maybe 5-10 CM longer than that and trim to
length.

-- Tom




"GeorgeF" wrote in message
ink.net...

1) Where can one buy a passband filter for 50-52MHz?

2) When talking about coax trimmed to length, are you talking about a coax
stub? Such as cut to 1/4 wavelength of the offending freq? If so would
be ends be shorted or let open? never worked with stubs yet....

TNX
George

"Tom" wrote in message
news:YBvjd.2272$bH2.1471@trnddc09...
Don't know where you can buy a passband filter. Maybe be able to find some
cavity type filters for 50 MHz, but probably only surplus. Building from
scratch
is easy but takes a network analyzer to tune.

A coax stub can be either open or shorted, your preference. Cheapest way
is
to
start with an open stub slightly too long and trim it to length. If you
can
borrow
a signal generator and power meter, then you can tune it that way.

It's practical to get about 25 dB of loss with a stub, better is difficult
due to losses
in the conectors, cables, etc.

You may achieve -25dB loss at CH2 video, but unfortunately you will also
have high loss at 50MHz, and a VSWR that is out of sight.
Build one and see for yourself.

Dale W4OP

Well, probably true. Don't transmit through it! The computer with the
shorted-stub
spreadsheet on it is broken, so I can't look at the loss vs. frequency. It's
a simple
Excel sheet that models the complex transmission-line equation (including
loss)
of the stub against the feedline. Hoped it wouldn't be that bad at 10%
separation,
but am flying blind until I can get access to it and run the numbers.

-- Tom



"Dale Parfitt" wrote in message
news:jZAjd.2538$bH2.1351@trnddc09...

"Tom" wrote in message
news:YBvjd.2272$bH2.1471@trnddc09...
Don't know where you can buy a passband filter. Maybe be able to find
some
cavity type filters for 50 MHz, but probably only surplus. Building from
scratch
is easy but takes a network analyzer to tune.

A coax stub can be either open or shorted, your preference. Cheapest way
is
to
start with an open stub slightly too long and trim it to length. If you
can
borrow
a signal generator and power meter, then you can tune it that way.

It's practical to get about 25 dB of loss with a stub, better is
difficult
due to losses
in the conectors, cables, etc.

You may achieve -25dB loss at CH2 video, but unfortunately you will also
have high loss at 50MHz, and a VSWR that is out of sight.
Build one and see for yourself.

Dale W4OP

"Dale Parfitt" ) writes:
"Tom" wrote in message
news:YBvjd.2272$bH2.1471@trnddc09...
Don't know where you can buy a passband filter. Maybe be able to find some
cavity type filters for 50 MHz, but probably only surplus. Building from
scratch
is easy but takes a network analyzer to tune.

A coax stub can be either open or shorted, your preference. Cheapest way
is
to
start with an open stub slightly too long and trim it to length. If you
can
borrow
a signal generator and power meter, then you can tune it that way.

It's practical to get about 25 dB of loss with a stub, better is difficult
due to losses
in the conectors, cables, etc.

You may achieve -25dB loss at CH2 video, but unfortunately you will also
have high loss at 50MHz, and a VSWR that is out of sight.
Build one and see for yourself.

Dale W4OP


So you get a crystal cut for the channel 2 carrier frequency, and find
a place to connect it in the receiver chain. This sort of thing was done
apparently in repeaters forty years ago, to keep the transmitter out of
the receiver. I do think one would have to modify the receiver because
the crystal might not be able to handle the transmitter signal.

Michael VE2BVW

OK. got access to the spreadsheet. Setting the stub+short+connector loss
to 0.25 dB, and cutting the stub for 55.25 gives about 15 dB loss at 50 MHz,
and about 30 dB loss at 55.25. This probably is good enough to either
prove or disprove the hypothesis about what is causing the problem (video
carrier overloading the RF amp), and an inexpensive way to find out.

As a long-term solution, a bandpass filter would be easier provided it had
loss low and SWR (so it could be left in-line for transmitting).

-- Tom




"Dale Parfitt" wrote in message
news:jZAjd.2538$bH2.1351@trnddc09...

"Tom" wrote in message
news:YBvjd.2272$bH2.1471@trnddc09...
Don't know where you can buy a passband filter. Maybe be able to find
some
cavity type filters for 50 MHz, but probably only surplus. Building from
scratch
is easy but takes a network analyzer to tune.

A coax stub can be either open or shorted, your preference. Cheapest way
is
to
start with an open stub slightly too long and trim it to length. If you
can
borrow
a signal generator and power meter, then you can tune it that way.

It's practical to get about 25 dB of loss with a stub, better is
difficult
due to losses
in the conectors, cables, etc.

You may achieve -25dB loss at CH2 video, but unfortunately you will also
have high loss at 50MHz, and a VSWR that is out of sight.
Build one and see for yourself.

Dale W4OP

Well, probably true. Don't transmit through it! The computer with the
shorted-stub
spreadsheet on it is broken, so I can't look at the loss vs. frequency. It's
a simple
Excel sheet that models the complex transmission-line equation (including
loss)
of the stub against the feedline. Hoped it wouldn't be that bad at 10%
separation,
but am flying blind until I can get access to it and run the numbers.

-- Tom



"Dale Parfitt" wrote in message
news:jZAjd.2538$bH2.1351@trnddc09...

"Tom" wrote in message
news:YBvjd.2272$bH2.1471@trnddc09...
Don't know where you can buy a passband filter. Maybe be able to find
some
cavity type filters for 50 MHz, but probably only surplus. Building from
scratch
is easy but takes a network analyzer to tune.

A coax stub can be either open or shorted, your preference. Cheapest way
is
to
start with an open stub slightly too long and trim it to length. If you
can
borrow
a signal generator and power meter, then you can tune it that way.

It's practical to get about 25 dB of loss with a stub, better is
difficult
due to losses
in the conectors, cables, etc.

You may achieve -25dB loss at CH2 video, but unfortunately you will also
have high loss at 50MHz, and a VSWR that is out of sight.
Build one and see for yourself.

Dale W4OP

Well, probably true. Don't transmit through it! The computer with the
shorted-stub
spreadsheet on it is broken, so I can't look at the loss vs. frequency. It's
a simple
Excel sheet that models the complex transmission-line equation (including
loss)
of the stub against the feedline. Hoped it wouldn't be that bad at 10%
separation,
but am flying blind until I can get access to it and run the numbers.

-- Tom



"Dale Parfitt" wrote in message
news:jZAjd.2538$bH2.1351@trnddc09...

"Tom" wrote in message
news:YBvjd.2272$bH2.1471@trnddc09...
Don't know where you can buy a passband filter. Maybe be able to find
some
cavity type filters for 50 MHz, but probably only surplus. Building from
scratch
is easy but takes a network analyzer to tune.

A coax stub can be either open or shorted, your preference. Cheapest way
is
to
start with an open stub slightly too long and trim it to length. If you
can
borrow
a signal generator and power meter, then you can tune it that way.

It's practical to get about 25 dB of loss with a stub, better is
difficult
due to losses
in the conectors, cables, etc.

You may achieve -25dB loss at CH2 video, but unfortunately you will also
have high loss at 50MHz, and a VSWR that is out of sight.
Build one and see for yourself.

Dale W4OP

"Dale Parfitt" ) writes:
"Tom" wrote in message
news:YBvjd.2272$bH2.1471@trnddc09...
Don't know where you can buy a passband filter. Maybe be able to find some
cavity type filters for 50 MHz, but probably only surplus. Building from
scratch
is easy but takes a network analyzer to tune.

A coax stub can be either open or shorted, your preference. Cheapest way
is
to
start with an open stub slightly too long and trim it to length. If you
can
borrow
a signal generator and power meter, then you can tune it that way.

It's practical to get about 25 dB of loss with a stub, better is difficult
due to losses
in the conectors, cables, etc.

You may achieve -25dB loss at CH2 video, but unfortunately you will also
have high loss at 50MHz, and a VSWR that is out of sight.
Build one and see for yourself.

Dale W4OP


So you get a crystal cut for the channel 2 carrier frequency, and find
a place to connect it in the receiver chain. This sort of thing was done
apparently in repeaters forty years ago, to keep the transmitter out of
the receiver. I do think one would have to modify the receiver because
the crystal might not be able to handle the transmitter signal.

Michael VE2BVW

"Dale Parfitt" ) writes:
"Tom" wrote in message
news:YBvjd.2272$bH2.1471@trnddc09...
Don't know where you can buy a passband filter. Maybe be able to find some
cavity type filters for 50 MHz, but probably only surplus. Building from
scratch
is easy but takes a network analyzer to tune.

A coax stub can be either open or shorted, your preference. Cheapest way
is
to
start with an open stub slightly too long and trim it to length. If you
can
borrow
a signal generator and power meter, then you can tune it that way.

It's practical to get about 25 dB of loss with a stub, better is difficult
due to losses
in the conectors, cables, etc.

You may achieve -25dB loss at CH2 video, but unfortunately you will also
have high loss at 50MHz, and a VSWR that is out of sight.
Build one and see for yourself.

Dale W4OP


So you get a crystal cut for the channel 2 carrier frequency, and find
a place to connect it in the receiver chain. This sort of thing was done
apparently in repeaters forty years ago, to keep the transmitter out of
the receiver. I do think one would have to modify the receiver because
the crystal might not be able to handle the transmitter signal.

Michael VE2BVW

OK. got access to the spreadsheet. Setting the stub+short+connector loss
to 0.25 dB, and cutting the stub for 55.25 gives about 15 dB loss at 50 MHz,
and about 30 dB loss at 55.25. This probably is good enough to either
prove or disprove the hypothesis about what is causing the problem (video
carrier overloading the RF amp), and an inexpensive way to find out.

As a long-term solution, a bandpass filter would be easier provided it had
loss low and SWR (so it could be left in-line for transmitting).

-- Tom




"Dale Parfitt" wrote in message
news:jZAjd.2538$bH2.1351@trnddc09...

"Tom" wrote in message
news:YBvjd.2272$bH2.1471@trnddc09...
Don't know where you can buy a passband filter. Maybe be able to find
some
cavity type filters for 50 MHz, but probably only surplus. Building from
scratch
is easy but takes a network analyzer to tune.

A coax stub can be either open or shorted, your preference. Cheapest way
is
to
start with an open stub slightly too long and trim it to length. If you
can
borrow
a signal generator and power meter, then you can tune it that way.

It's practical to get about 25 dB of loss with a stub, better is
difficult
due to losses
in the conectors, cables, etc.

You may achieve -25dB loss at CH2 video, but unfortunately you will also
have high loss at 50MHz, and a VSWR that is out of sight.
Build one and see for yourself.

Dale W4OP