Jeff Liebermann wrote:

There are calculators that will predict the isolation.
......
"Minimum Tx and Rx frequency difference: VHF 3.5Mhz"
That's not going to work with 0.6MHz spacing on the 2m ham band.

This is what a proper (Phelps-Dodge) 2m duplexer looks like:
http://www.LearnByDestroying.com/k6bj/K6BJ%20Repeater/slides/2m%20duplexer2.html
Note the much large size cavities.

Thanks, that's exactly what I needed to know.

Geoff.


--
Geoffrey S. Mendelson N3OWJ/4X1GM
Making your enemy reliant on software you support is the best revenge.

"Geoffrey S. Mendelson" wrote in message
...


snip


Geoff.


If your intent is to experiment with the cheap duplexer, what I have to
offer is irrelevant. However, if you aim to build a repeater, consider
getting your isolation over distance (much greater than 10m). Put the
transmitter and receiver a few km apart and link them using another band
authorized in your area (440?).

I encountered this in Key West Florida some years ago. Worked fine there.

"Sal"

Sal wrote:

"Geoffrey S. Mendelson" wrote in message
...


snip


Geoff.


If your intent is to experiment with the cheap duplexer, what I have to
offer is irrelevant. However, if you aim to build a repeater, consider
getting your isolation over distance (much greater than 10m). Put the
transmitter and receiver a few km apart and link them using another band
authorized in your area (440?).

I encountered this in Key West Florida some years ago. Worked fine there.

It is done here on 10m, where the duplex offset is only 100 kHz and
a duplexer is physically very large.

However, what I hear from the repeater team is that one is in fact
building and maintaining 2 repeaters, doubling the chance of any faults
and problems. Setting up the 10m repeater was much more work than
everyone envisioned, and many had experience on 70cm etc.

"Rob" wrote in message
...
Sal wrote:

"Geoffrey S. Mendelson" wrote in message
...


snip


Geoff.


If your intent is to experiment with the cheap duplexer, what I have to
offer is irrelevant. However, if you aim to build a repeater, consider
getting your isolation over distance (much greater than 10m). Put the
transmitter and receiver a few km apart and link them using another band
authorized in your area (440?).

I encountered this in Key West Florida some years ago. Worked fine
there.

It is done here on 10m, where the duplex offset is only 100 kHz and
a duplexer is physically very large.

However, what I hear from the repeater team is that one is in fact
building and maintaining 2 repeaters, doubling the chance of any faults
and problems. Setting up the 10m repeater was much more work than
everyone envisioned, and many had experience on 70cm etc.

Yup. Two repeaters. But avoiding "cans" just might be a blessing.

My local club has a repeater using new electronics but an old duplexer.
I hate periodically re-tweaking the duplexer but
I'm the only one with the spec-an/tracking generator, so I'm it.

The repeater maintenance budget will handle a new duplexer soon.
Hallelujah!

Sal

On 8/30/2011 1:26 PM, Rob wrote:
wrote:

"Geoffrey S. wrote in message
...


snip


Geoff.


If your intent is to experiment with the cheap duplexer, what I have to
offer is irrelevant. However, if you aim to build a repeater, consider
getting your isolation over distance (much greater than 10m). Put the
transmitter and receiver a few km apart and link them using another band
authorized in your area (440?).

I encountered this in Key West Florida some years ago. Worked fine there.

It is done here on 10m, where the duplex offset is only 100 kHz and
a duplexer is physically very large.

However, what I hear from the repeater team is that one is in fact
building and maintaining 2 repeaters, doubling the chance of any faults
and problems. Setting up the 10m repeater was much more work than
everyone envisioned, and many had experience on 70cm etc.


What about VoIP using 802.11 as the link. These days, that might be
easier than trying to cobble up a 440 remote link.

Jim Lux wrote:
On 8/30/2011 1:26 PM, Rob wrote:
wrote:

"Geoffrey S. wrote in message
...


snip


Geoff.


If your intent is to experiment with the cheap duplexer, what I have to
offer is irrelevant. However, if you aim to build a repeater, consider
getting your isolation over distance (much greater than 10m). Put the
transmitter and receiver a few km apart and link them using another band
authorized in your area (440?).

I encountered this in Key West Florida some years ago. Worked fine there.

It is done here on 10m, where the duplex offset is only 100 kHz and
a duplexer is physically very large.

However, what I hear from the repeater team is that one is in fact
building and maintaining 2 repeaters, doubling the chance of any faults
and problems. Setting up the 10m repeater was much more work than
everyone envisioned, and many had experience on 70cm etc.


What about VoIP using 802.11 as the link. These days, that might be
easier than trying to cobble up a 440 remote link.

At first they used (or planned using) an FM link on 23cm, then they
switched to digital voice over 802.11a (6cm), then to 802.11g on 13cm,
and I think they now use a wired internet connection.

On 8/30/2011 5:13 PM, Jim Lux wrote:

What about VoIP using 802.11 as the link. These days, that might be
easier than trying to cobble up a 440 remote link.

Joy!

I am going to sit back and see how this suggestion evolves.

tom
K0TAR

tom wrote:

I am going to sit back and see how this suggestion evolves.

Look at SVXLINK. It's an open source package that runs on Linux (and possibly
BSD) that does exactly that.

It includes support for remote receivers (with a voting option), remote
transmitters, and an echolink server.

We plan to use it with hard wired internet links, but who knows, an 802.11
link could work. Unlike the US we are restricted to 100mW EIRP, so no
gain antennas, etc, to make things work better.

Geoff.


--
Geoffrey S. Mendelson N3OWJ/4X1GM
Making your enemy reliant on software you support is the best revenge.

Geoffrey S. Mendelson wrote:
We plan to use it with hard wired internet links, but who knows, an 802.11
link could work. Unlike the US we are restricted to 100mW EIRP, so no
gain antennas, etc, to make things work better.

Do you have a transmit ban on 802.11 channels in 4X too?

We as hams in the Netherlands are no longer allowed to transmit above
2400 MHz except to an amateur satellite.

On Tue, 30 Aug 2011 13:04:48 -0700, "Sal" wrote:

If your intent is to experiment with the cheap duplexer, what I have to
offer is irrelevant. However, if you aim to build a repeater, consider
getting your isolation over distance (much greater than 10m). Put the
transmitter and receiver a few km apart and link them using another band
authorized in your area (440?).

I encountered this in Key West Florida some years ago. Worked fine there.

How fine is fine?

That last time I did that (about 30 years ago), on a commercial
system, there was a huge difference in transmit and receive footprint.
Some locations could hear but not talk. Others were the other way
around. Either way, the customers were not thrilled. We went back to
one antenna per radio.

We then repeated the same mistake with a common receive antenna at the
very top of the tower, followed by an RF amp, and then an 8 way
splitter. Attach 8 receivers and you only need one RX antenna.
Unfortunately, the amplifier was too easily overloaded, and the
splitter did not provide sufficient isolation to prevent the local
oscillator leakage from creating new receiver spurs. I later added
cavities and isolators to solve that problem, which increased the cost
sufficiently that 8 TX/RX antennas would have been cheaper. (Except
for the tower space rental, but we owned the building and towers).
Also, with a single RX antenna on 8 radios, it makes a great single
point of failure for lightning hits. It was easy to tell if the RF
Amp had taken a hit. The office would simultaneously get dozens of
irate service outage calls (These were community repeaters with up to
15 customers per repeater). I would never want to be the top antenna
on a tower, no matter what the range benefits.

9 repeater in one rack. Notice the lack of duplexers.
http://802.11junk.com/jeffl/pics/Old%20Repeaters/slides/Santiago-01.html

Here's the corresponding transmit antenna intermod generator:
http://802.11junk.com/jeffl/pics/Old%20Repeaters/slides/LoopMtn02.html
The receive antenna is behind me, on top of another telephone pole.

Yet another great idea was to physically separate the transmitter and
receiver buildings on a mountain top. That was Verdugo Pk in the San
Fernando Valley. Sorry, no photos handy. This had some real
advantages, especially at low band (30-50Mhz). The problem was that
with all the transmitters jammed into one building, with little
physical isolation among the antennas, there's was considerable
intermod caused by the various TX mixes. Since the original
justification for this great idea was to solve the intermod problem,
this was also loser.

Much as I don't like duplexers, isolators, cavities, lightning
arrestors, fat coax, and omni antennas, the combination is the
solution that seems to work the best. All the other great ideas are
far worse, more expensive, or deficient in some manner.

http://802.11junk.com/jeffl/pics/Old%20Repeaters/

Guess what's happening with this antenna problem?
http://802.11junk.com/jeffl/pics/Old%20Repeaters/slides/LoopMtn03.html
Incidentally, that's where I was cleaning up the mess and almost
picked up what I thought was a piece of black coax. It was a snake.

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