Chinese duplexers
 

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.

Chinese duplexers
 

"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

Chinese duplexers
 

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

Chinese duplexers
 

"Jeff Liebermann" wrote in message
...
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?

Good question. Coverage was entirely satisfactory over the entire island
and several miles up the Overseas Highway. I never used anything more
exotic than a rubber duck. However, Key West is small and all the keys are
very flat.

"Sal"

Chinese duplexers
 

Jim Lux wrote:

Any reason why you're using a split of 600kHz? Why not go to a
non-standard split to make life easier. Pick two frequencies 3 MHz apart
(assuming you can get them coordinated, which is more a political than a
technical issue)

Thanks for the advice and information.

I'm not in the US. 3Mhz split is more than my entire 2m band. :-(

Geoff.


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

Chinese duplexers
 

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?).

Acutally that's the real purpose of the whole experiement. We are looking
at setting up a system of internet linked remote inputs (and possibly
low power local outputs) using Linux and SVXLINK.

Right now the final destination is an Echolink type node (SVXLINK also
acts as an Echolink server), but one of the things we wanted to experiment
with is an actual repeater.

Thanks,

Geoff.


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

Chinese duplexers
 

Jeff Liebermann wrote:

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.

That's basically our problem. The repeater we want to use was developed
with the criterea that if you parked your car, turned on your 25 watt
or higher radio with a 5/8 wave whip and was able to "kerchunk" the
repeater, the area was "covered". This coverage was mapped out around 1990.

Since then population has expanded, new housing has been built and new hams
have become licensed. 2011 critera is in order to be covered, a ham with
a watt HT has to be able to be understood.

The main repeater in question is able to reach the sea twoard the north west
to the southwest (about 35 miles), but can't even be heard 2-3 KM to the north
in spots, and has almost no reception to the southeast.

Our proposed solution is not radio links as they are a expensive, need to
be mainainted on site, etc. Internet remote receivers are very cheap, for
example, an HT an interface to the computer and an old P4 (needs built in
ethernet) makes a useable one and costs a couple of dollars a month in
electrcity. Obvously the location has to have decent internet bandwidth
with 64k bits per second spare.

Performance can be improved with a better radio and antenna, but in some
places, there is only one ham that needs to be "covered".

There may even be real money for real equipment later, but not now.

Geoff.


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

Chinese duplexers
 

Sal wrote:

Good question. Coverage was entirely satisfactory over the entire island
and several miles up the Overseas Highway. I never used anything more
exotic than a rubber duck. However, Key West is small and all the keys are
very flat.

That's our problem. Jerusalem is high (3,000 feet ASL) and loaded with hills.
There are spots in the city where there is no cell phone coverage. The cell
phone companies go nuts trying to fill the holes, but there is a lot of NIMBY
here.

Geoff.


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

Chinese duplexers
 

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.

Chinese duplexers
 

On Wed, 31 Aug 2011 05:59:04 +0000 (UTC), "Geoffrey S. Mendelson"
wrote:

Our proposed solution is not radio links as they are a expensive, need to
be mainainted on site, etc. Internet remote receivers are very cheap,
(...)

You might want to look at:
http://www.wb6ece.org
Simulcast and voting from 7 sites with GPS locked oscillators.

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