seperation in lie of a duplexer at 222 mhz band
 

haing gotten many of the peices of a 222 band repater and wanting to
put it on the air how much sepertion is required to avoid a paying the
price of a duplexer at 22 band

any assiatnce welcome

seperation in lie of a duplexer at 222 mhz band
 

On 21 May 2006 14:17:19 -0700, "an old friend"
wrote:

haing gotten many of the peices of a 222 band repater and wanting to
put it on the air how much sepertion is required to avoid a paying the
price of a duplexer at 22 band

any assiatnce welcome

Depending on the transmitter and receiver type, good ones will require
around 75 to 85 db of isolation at least.

30 feet of vertical seperation of antennas will give around 60 db of
isolation.
60 feet of vertical isolation may give around 70 db of isolation.
After that it starts to flatten out.

600 feet of horizontal seperation will give around 60 db of isolation.
It will take doubling the distance for an additional each 6 db of
isolation

73
Gary K4FMX

seperation in lie of a duplexer at 222 mhz band
 

In article .com,
an old friend wrote:

haing gotten many of the peices of a 222 band repater and wanting to
put it on the air how much sepertion is required to avoid a paying the
price of a duplexer at 22 band

That depends to some extent on the design of your receiver. Different
designs have different RF-signal thresholds at which front-end
desensitization will become a problem. A receiver with a
broadly-tuned front end (e.g. some converted Motorola radios, most
mobile ham rigs) is likely to be more prone to desense than a
dedicated single-frequency receiver board having several stages of
narrowly-tuned helical resonator in the RF chain.

It'll also depend on how clean your transmitter is. Broadband noise
and spurs from the transmitter can cause problems for the receiver by
"swamping" the desired signal with noise, independent of whatever
desensitization the main transmit signal causes to the receiver
front-end.

My old copy of ARRL's "FM and Repeaters" book (copyright 1972)
suggests that approximately 58 dB of attenuation is required for a 600
kHz transmit/receive offset. They don't give a suggested figure for
the wider 1.6 MHz offset used on the 222 band.

According to the graphs in this book, achieving 58 dB of attenuation,
on the 222 band, requires approximately 20 feet of vertical separation
between antennas, or approximately 100 feet of horizontal separation,
assuming unity-gain antennas (e.g. halfwave dipoles). You'd need
greater horizontal separation when using antennas with gain over a
halfwave. You might be able to get by with less vertical separation
if using gain antennas, depending on the actual pattern, feedline
radiation, local reflections, and so forth.

You might want to Google around for articles which show a method for
homebrewing a duplexer, using a length of surplus large-diameter
hardline coaxial cable as the resonator. These have apparently been
used for several years on the 6-meter band, and I recently saw a
Heliax notch/pass resonator which was made for a local 2-meter
repeater (it adds one additional section of receive
filtering/isolation to a repeater which uses a single antenna and a
commercially-built two-transmit-can, two-receive-can duplexer). The Q
of such Heliax-based resonators is lower than that of conventional
cans, and the insertion losses are higher.

If you don't want to install a full-fledged duplexer and use a single
antenna, you might try something like a pair of 222 antennas with 20
foot or more of vertical separation, plus one band-reject (or
band-pass band-reject) Heliax resonator on each one.

http://www.dallas.net/~jvpoll/dup6m/dup6m.html would be one place to
start looking.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

seperation in lie of a duplexer at 222 mhz band
 

Dave Platt wrote:
In article .com,
an old friend wrote:

haing gotten many of the peices of a 222 band repater and wanting to
put it on the air how much sepertion is required to avoid a paying the
price of a duplexer at 22 band
cut for brevity
My old copy of ARRL's "FM and Repeaters" book (copyright 1972)
suggests that approximately 58 dB of attenuation is required for a 600
kHz transmit/receive offset. They don't give a suggested figure for
the wider 1.6 MHz offset used on the 222 band.

According to the graphs in this book, achieving 58 dB of attenuation,
on the 222 band, requires approximately 20 feet of vertical separation
between antennas, or approximately 100 feet of horizontal separation,
assuming unity-gain antennas (e.g. halfwave dipoles). You'd need
greater horizontal separation when using antennas with gain over a
halfwave. You might be able to get by with less vertical separation
if using gain antennas, depending on the actual pattern, feedline
radiation, local reflections, and so forth.
ty for that given the proposed is a pair of disused grain silos 80 feet
a part I was thinking horizontal sepertion (frankly had not considered
vertical at all or i would have made that

You might want to Google around for articles which show a method for
homebrewing a duplexer, using a length of surplus large-diameter
hardline coaxial cable as the resonator. These have apparently been
used for several years on the 6-meter band, and I recently saw a
Heliax notch/pass resonator which was made for a local 2-meter
repeater (it adds one additional section of receive
filtering/isolation to a repeater which uses a single antenna and a
commercially-built two-transmit-can, two-receive-can duplexer). The Q
of such Heliax-based resonators is lower than that of conventional
cans, and the insertion losses are higher.

If you don't want to install a full-fledged duplexer and use a single
antenna, you might try something like a pair of 222 antennas with 20
foot or more of vertical separation, plus one band-reject (or
band-pass band-reject) Heliax resonator on each one.

http://www.dallas.net/~jvpoll/dup6m/dup6m.html would be one place to
start looking.
I had read something of that but have never been any good at cuting
stuff right (i end up with lots of scrap

i have just hearing folks with with radio that have some 22 band (a
kenwood tribander has been popular round here) and no reapters localy
that use it I am planing on trying to put together a decent repater
that work at least out then goping after I ge it u and let be know at
that point it exists maybe some folks that could help with hombrewing a
duplexer will step up to improve the system

ty for the info

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

seperation in lie of a duplexer at 222 mhz band
 

I see that English isn`t your mother tongue then !!!.......or are you just
kidding??.... ;-)

Lee......G6ZSG.....

"an_old_friend" wrote in message
oups.com...

Dave Platt wrote:
In article .com,
an old friend wrote:

haing gotten many of the peices of a 222 band repater and wanting to
put it on the air how much sepertion is required to avoid a paying the
price of a duplexer at 22 band
cut for brevity
My old copy of ARRL's "FM and Repeaters" book (copyright 1972)
suggests that approximately 58 dB of attenuation is required for a 600
kHz transmit/receive offset. They don't give a suggested figure for
the wider 1.6 MHz offset used on the 222 band.

According to the graphs in this book, achieving 58 dB of attenuation,
on the 222 band, requires approximately 20 feet of vertical separation
between antennas, or approximately 100 feet of horizontal separation,
assuming unity-gain antennas (e.g. halfwave dipoles). You'd need
greater horizontal separation when using antennas with gain over a
halfwave. You might be able to get by with less vertical separation
if using gain antennas, depending on the actual pattern, feedline
radiation, local reflections, and so forth.
ty for that given the proposed is a pair of disused grain silos 80 feet
a part I was thinking horizontal sepertion (frankly had not considered
vertical at all or i would have made that

You might want to Google around for articles which show a method for
homebrewing a duplexer, using a length of surplus large-diameter
hardline coaxial cable as the resonator. These have apparently been
used for several years on the 6-meter band, and I recently saw a
Heliax notch/pass resonator which was made for a local 2-meter
repeater (it adds one additional section of receive
filtering/isolation to a repeater which uses a single antenna and a
commercially-built two-transmit-can, two-receive-can duplexer). The Q
of such Heliax-based resonators is lower than that of conventional
cans, and the insertion losses are higher.

If you don't want to install a full-fledged duplexer and use a single
antenna, you might try something like a pair of 222 antennas with 20
foot or more of vertical separation, plus one band-reject (or
band-pass band-reject) Heliax resonator on each one.

http://www.dallas.net/~jvpoll/dup6m/dup6m.html would be one place to
start looking.
I had read something of that but have never been any good at cuting
stuff right (i end up with lots of scrap

i have just hearing folks with with radio that have some 22 band (a
kenwood tribander has been popular round here) and no reapters localy
that use it I am planing on trying to put together a decent repater
that work at least out then goping after I ge it u and let be know at
that point it exists maybe some folks that could help with hombrewing a
duplexer will step up to improve the system

ty for the info

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

seperation in lie of a duplexer at 222 mhz band
 

There is a local repeater system here that was put together by an
impoverished college student many years ago. He didn't have much
money for duplexers, but he did have the gift of persuasion. He was
able to talk his way on to 4 towers scattered about town. He has
transmitters and receivers for 6m, 2m, 1.25m, and 75cm spread over the
four towers, all cross-linked. No tower has a transmitter and a
receiver on the same band. Each tower is 15 to 20 miles from the next
tower.

Ed

On 21 May 2006 14:17:19 -0700, "an old friend"
wrote:

haing gotten many of the peices of a 222 band repater and wanting to
put it on the air how much sepertion is required to avoid a paying the
price of a duplexer at 22 band

any assiatnce welcome

seperation in lie of a duplexer at 222 mhz band
 

On Mon, 29 May 2006 23:15:07 -0500, Ed Bailen wrote:

There is a local repeater system here that was put together by an
impoverished college student many years ago. He didn't have much
money for duplexers, but he did have the gift of persuasion. He was
able to talk his way on to 4 towers scattered about town. He has
transmitters and receivers for 6m, 2m, 1.25m, and 75cm spread over the
four towers, all cross-linked. No tower has a transmitter and a
receiver on the same band. Each tower is 15 to 20 miles from the next
tower.

Ed

On 21 May 2006 14:17:19 -0700, "an old friend"
wrote:

haing gotten many of the peices of a 222 band repater and wanting to
put it on the air how much sepertion is required to avoid a paying the
price of a duplexer at 22 band


This does add the complexity of requiring multiple receivers, links,
sites and a voter to get even coverage, but if the equipment is
available, it works, or can work very well and you do not have the
ticklish process of setting up a series of band pass/band stop cans
which is usually three on transmit and three on receive.

I have forgotten the specific distance required for
separation/isolation, but it's considerable and I believe it's close
to a mile, maybe more. I'm sure some one on here can come up with the
specifics.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

any assiatnce welcome

seperation in lie of a duplexer at 222 mhz band
 

Dave has some good info too, but here's some background.

Transmitters ALL have noise coming out that decreases as you move away from
the carrier. We call this sideband noise. This noise can cover up your
received signal if it is high enough (which is not difficult) on the receive
frequency. A duplexer or cavity set can (if needed) have a notch at the
_RX_ frequency to reduce this noise. Cavities like this are called
"pass-reject" cavities because they have a band-pass characteristic for the
transmitter frequency and a notch which can also be tuned to the receiver
frequency to reduce this noise more than the simple cavity skirts can.

Transmitters can have spurs and if you have that, you have a similar problem
because it is just a single frequency which could cover a received signal
and you must reduce. However, chances of having a spur on your receiver
frequency is rare (though synthesizers can cause quite a few near the
carrier, so you want to stay away from a synthesized radio if possible, for
a repeater, for that reason)

While we talk of "receiver overload, blocking, desense" receivers have one
characteristic which is not obvious to most. Since ALL oscillators have
this sideband noise mentioned above, the local oscillator IN the receiver
also has some. When a strong carrier enters the receiver (your own
transmitter), _it_ becomes another local oscillator in the mixer and can mix
with the sideband noise of the intentional LO. This mixes some part of the
sideband noise of the LO onto the desired frequency. This is one of the
mechanisims for receiver desense and one reason to reduce the amount of TX
power getting to the receiver. With synthesixed receivers, it CAN be the
dominant cause for desense. This is because the VCOs needed for
synthesizers typically can have quite high sideband noise. Since a typical
radio is not designed for repeater operation, it's design will not try to
optimize for sideband noise.

On 2M you can probably hear this effect with just about any two 2M ham rigs.
Talk to someone on the local repeater, but not too close to the repeater
(I'd say at least 5 miles away) and drive close to each other. At some
point he repeater will get noisy and if you have a good ear, you can hear
that this noise is different than the normal, weak signal noise. When the
other station de-keys, the repeater will quiet with it's normal gusto.

73, Steve, K9DCI