installing isolator on a transceiver
 

We have 2M packet node transceivers at a new government radio site. The
new site owner requires isolators be installed on all transmitters. As you
might surmise, it doesn't seem possible to do so on a simplex one RF port
radio such an Alinco DR-135.

Anyone out there with some realistic suggestions on how we might manage
to do this?

Ed K7AAT

installing isolator on a transceiver
 

Ed wrote:
We have 2M packet node transceivers at a new government radio site. The
new site owner requires isolators be installed on all transmitters. As you
might surmise, it doesn't seem possible to do so on a simplex one RF port
radio such an Alinco DR-135.

Anyone out there with some realistic suggestions on how we might manage
to do this?

Ed K7AAT

Maybe just an RF isolator in the AC line?

MTV

installing isolator on a transceiver
 

On 9 dic, 22:07, Ed wrote:
* We have 2M packet node transceivers at a new government radio site. * The
new site owner requires isolators be installed on all transmitters. *As you
might surmise, it doesn't seem possible to do so on a simplex one RF port
radio such an Alinco DR-135.

* Anyone out there with some realistic suggestions on how we might manage
to do this?

* Ed * K7AAT

Hello Ed,

Is this because of intermodulation products due to the non-linear
behavior of the PA? If the site owner is technical, you might discuss
a band pass filter as this also reduces undesired mixing of other
signals in your equipment's PA.

Best regards,

Wim
PA3DJS
www.tetech.nl
Don't forget to remove abc in case of PM.

installing isolator on a transceiver
 

On 09 Dec 2009 21:07:18 GMT, Ed wrote:



We have 2M packet node transceivers at a new government radio site. The
new site owner requires isolators be installed on all transmitters. As you
might surmise, it doesn't seem possible to do so on a simplex one RF port
radio such an Alinco DR-135.

Anyone out there with some realistic suggestions on how we might manage
to do this?

Ed K7AAT

Are you confusing an isolator with a duplexer?

73's
Richard Clark, KB7QHC

installing isolator on a transceiver
 

In article ,
Ed wrote:

We have 2M packet node transceivers at a new government radio site. The
new site owner requires isolators be installed on all transmitters. As you
might surmise, it doesn't seem possible to do so on a simplex one RF port
radio such an Alinco DR-135.

Anyone out there with some realistic suggestions on how we might manage
to do this?

You could probably do this with an isolator, a pair of SPDT coaxial
relays, and some modifications to the PTT circuitry between the rig
and the TNC.

You'd install the SPDT relays between the radio and the antenna.
Between the "normally closed" switchable ports, install a coaxial
number. Between the "normally open" ports, connect the isolator.

Take the PTT signal coming out of the TNC, and feed it to a bit of
circuitry (possibly analog, possibly discrete digital, possibly a
little 8-pin PIC micro). The effect of this circuitry would be detect
PTT from the TNC, drive a signal to the relays to switch them "on",
delay about 10 milliseconds (long enough for the relays to switch, and
stop bouncing), and then feed PTT to the radio. When PTT from the TNC
is deasserted, drop PTT to the radio immediately, wait around 10
milliseconds, and then turn off the relays.

--
Dave Platt AE6EO
Friends of 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!

installing isolator on a transceiver
 

On 09 Dec 2009 21:07:18 GMT, Ed wrote:

We have 2M packet node transceivers at a new government radio site. The
new site owner requires isolators be installed on all transmitters. As you
might surmise, it doesn't seem possible to do so on a simplex one RF port
radio such an Alinco DR-135.

The isolator has to go between the PA stage, after the low pass
filter, but before the T/R switch. That will require some surgery
inside the radio to bring out two coax cables to the external
isolator.

I'm rather surprised that a government site would allow a DR-135T
radio. While the DR-135T is perfectly suitable for a stand alone
packet radio application, such radios don't do very well in an high RF
polluted environment.

Has anyone done an intermod calculation for all the radios in the
building?

Anyone out there with some realistic suggestions on how we might manage
to do this?
Ed K7AAT

See above. If the site manager is fairly liberal, you might be able
to convince him that a simple bandpass cavity will suffice. It should
work because your packet box is running simplex. Even if he demands
an isolator, you still should have some manner of cavity BPF in the
line. I don't mean a little tiny soda can size cavity, but rather
something larger, with skirts that are way down. See cavity on the
left:
http://www.LearnByDestroying.com/k6bj/K6BJ%20Repeater/slides/2m%20rx%20cavity.html

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

installing isolator on a transceiver
 

In article ,
MTV wrote:

Maybe just an RF isolator in the AC line?

That would be solving an entirely different problem.

At many sites, it's necessary to install an isolator/circulator
between each transmitter and antenna. This prevents strong RF signals
from *other* transmitters at the site from coming back down the
feedline into your energized transmitter, intermodulating with your
own signal in the transmitter's finals, and bleeding nasty intermod
products back out up into your antenna.

This is a bit tricky to do if your radio doesn't have separate
"transmit out" and "receive in" ports. If you stick an isolator
between a single-poort transceiver and its antenna, the receiver won't
hear the incoming signal very well at all.. most of the received
signal power will be circulated away into the circulator's dummy load.

You either need to open up the transceiver and separate out the TX and
RX ports, or figure some way to bypass the circulator (e.g. a pair of
relays) when receiving.

--
Dave Platt AE6EO
Friends of 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!

installing isolator on a transceiver
 

We have 2M packet node transceivers at a new government radio site.
The
new site owner requires isolators be installed on all transmitters.
As you might surmise, it doesn't seem possible to do so on a simplex
one RF port radio such an Alinco DR-135.

Anyone out there with some realistic suggestions on how we might
manage
to do this?

Ed K7AAT



Thanks to those who have responded already. I was hoping for some
elegant solution I had not thought of, but so far nothing has come to
light. Also I was hoping there would be some way to implement this
wihthout relays.... but maybe not.

Regarding the comment about breaking out the Rx line to a separate
output... that might be possible but its solid state switching and would
be somewhat tricky to implement right after this solid state PA module
output.

One reason I hate the thought of adding antenna relays to switch the Rx
around the isolator is that this is a busy packet node and I don't like
the reliability issues a couple of added relays might add to a presently
solid state switched radio.. . although I could do this if forced to.

We have operated at this site since before the new vault was built and
all present customers simply moved over to it so to answer the question
posed, no ... no calculations have been done... but the new owner
"requires" isolators. The best solution for this situaion might be to
gather a few respected technical persons who this non-technical site
owner is familiar with and perhaps convince him this isn't necessary.

OR.. we could easily add a pass cavity of two and hope that this
would passify him.

We will see.

I'm still open to another other new or inovative solutions.

Thanks.

Ed K7AAT

installing isolator on a transceiver
 

Dave Platt wrote:
In article ,
MTV wrote:

Maybe just an RF isolator in the AC line?

That would be solving an entirely different problem.

At many sites, it's necessary to install an isolator/circulator
between each transmitter and antenna. This prevents strong RF signals
from *other* transmitters at the site from coming back down the
feedline into your energized transmitter, intermodulating with your
own signal in the transmitter's finals, and bleeding nasty intermod
products back out up into your antenna.

This is a bit tricky to do if your radio doesn't have separate
"transmit out" and "receive in" ports. If you stick an isolator
between a single-poort transceiver and its antenna, the receiver won't
hear the incoming signal very well at all.. most of the received
signal power will be circulated away into the circulator's dummy load.

You either need to open up the transceiver and separate out the TX and
RX ports, or figure some way to bypass the circulator (e.g. a pair of
relays) when receiving.


Thanks for the info
MTV

installing isolator on a transceiver
 

Thanks to those who have responded already. I was hoping for some
elegant solution I had not thought of, but so far nothing has come to
light. Also I was hoping there would be some way to implement this
wihthout relays.... but maybe not.

Regarding the comment about breaking out the Rx line to a separate
output... that might be possible but its solid state switching and would
be somewhat tricky to implement right after this solid state PA module
output.

One reason I hate the thought of adding antenna relays to switch the Rx
around the isolator is that this is a busy packet node and I don't like
the reliability issues a couple of added relays might add to a presently
solid state switched radio.. . although I could do this if forced to.

Another option is to buy a second radio, and use it for the receive
channel. Your existing transceiver would be used solely as a
transmitter, and could thus be hard-wired to an isolator.

You'd need to run the receiver on a different antenna, or have some
form of switchable protection circuit to keep it from having its
brains blown out by the transmitter.

--
Dave Platt AE6EO
Friends of 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!