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

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

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!

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

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.

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

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!

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

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

On 10 Dec 2009 00:06:16 GMT, Ed wrote:

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 T/R switches using the stock reed relays that come with Mitrek
radios on several 420Mhz links. My guess about 1,000 cycles per day.
The average lifetime for the reeds is about 2 years. I've lost count
how many reeds I've replaced. Fortunately, Digikey has a nice
assortment of reeds. I hear the Mitrek packet boxes are about the
same, although that's not my headache. If you're going to do the
external T/R switch, think solid state.

no calculations have been done...

Do them. I manage a local site stuffed full of assorted xmitters.
I've prevented disaster more than once with some simple calculations.

http://www3.telus.net/PassiveRF/
http://www.tcstx.com/software/Intermodulation.cfm

but the new owner
"requires" isolators.

That's just the beginning. The site I run is rather loose. Mostly
hams and junk. So far, there's been no need for a major cleanup,
although I'm tempted. From memory, some other sites requi
1. Circulators *AND* cavities on all xmitters.
2. Demonstrate that spurious tx rubbish is -60dB down.
3. Heliax everywhere.
4. No dissimilar metals on the coax connectors and adapters.
5. No nickel plating on anything carrying RF. (no Radio Shack junk)
6. All modems, routers, computers, and must be in a metal box with
RFI/EMI protection.
7. Remote on/off switching (to disable the xmitter if it goes
insane).
8. Posted current licenses (FCC requirement).
9. Lightning protection everywhere.
10. Shielded and grounded data lines (CAT5).

Here's what CDF (Cal Fire) requires to share their vault:
http://webmain02.fire.ca.gov/pubs/issuance/8000/rvsapp.pdf
I've seen worse.

Ah, I found one that's worse:
http://www.elsinorepeak.com/documents.html
Ummm... don't let the new site owner see these.

Incidentally, I spent several months trying to identify the source of
an intermod mix that was wrecking one of the ham repeaters. It would
come and go with no obvious pattern, making it difficult to find. I
finally got lucky by breaking protocol and unplugging customers
equipment while listening for changes. The last desperation act was
to unplug the 117VAC to 24VDC battery charger for the diesel
generator. That was it. The problem was that it was completely
shielded in both the case and the in/out wires. It was also directly
below the antenna structure, which is a low radiation location. The
moral is "That which is most obvious correct, beyond all need of
checking, is usually the problem". Do things the *RIGHT* way.

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.

Well, intimidation does work. Make sure your respected technical
people bring along some muscle. If that doesn't work, try beer or
wine.

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

The cavity will work well enough if you don't have any other xmitters
on nearby frequencies in the building. However, as one of those
technical types, my never humble opinion is that the DR-135T is not
the best of radios and will need all the protection you can provide.

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

Plan A:
Hybrid Ring Duplexer.
http://www.repeater-builder.com/antenna/hybridring.html
It should give enough isolation so that you can run the receiver full
time without a T/R switch. The problem is that I'm not sure it will
work on a single frequency. I gotta do some RTFM first. You'll still
need to bring out the receiver input coax, but at least there's no
external T/R switch or relays. Also, put something on the receiver
input to keep from blowing it up if there's too much VSWR.

Plan B:
Build a clone of the internal DR-135T T/R antenna switch. Bring out
the TX and RX coaxes externally. Install a cavity in the antenna line
and an isolator in the TX line. Install the T/R switch near the
antenna junction.

Plan C: Use 2 radios, one for TX and one for RX.

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