Chinese duplexers
 

I was looking at cheap HT's last night on eBay and I found several vendors
selling duplexers for repeater use. They sell for about $60 each.

They are 6 cavity (three transmit, three receive) and the closest they can
go on VHF is 3.5mHz.

Doing a web search I find they are not very good (what did you expect?)
but with a good front end they will work ok.

My problem is not only one of money (don't tell me to not waste my money
and buy a good, one, I can't afford it), but my 2m band is only 144-146
mHz, and the repeater portion is really just 145-146. I'm also limited
to 20w output.

So my question is anyone familar with them? Is it possible to take one
and convert it to a 6 cavity input filter? For example, I could put the
input on one side my yard and the output on the other, about 30 feet apart.

For example, if the input of the repeater was 145.600, could I have them
both tuned to 145.600 and connect the input of the receiver to one
set of cavities, the antenna to the other and leave the antenna connection
untouched, effectively placing them in series?

Thanks in advance,

Geoff.






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

Chinese duplexers
 

Geoffrey S. Mendelson wrote:
So my question is anyone familar with them? Is it possible to take one
and convert it to a 6 cavity input filter? For example, I could put the
input on one side my yard and the output on the other, about 30 feet apart.

No. There are two sides, one of them for the high frequency and the
other for the low frequency. The filter response is such that it passes
on one frequency and notches on the other.

Chinese duplexers
 

Rob wrote:

No. There are two sides, one of them for the high frequency and the
other for the low frequency. The filter response is such that it passes
on one frequency and notches on the other.

Ok thanks. Note that they are tunable anywhere in the 136-17? range.

Assuming the pass side is set to pass 145.600 (the input) and the notch
side is set to notch out 145.000 (the output) and they are connected in
series, would that work?

Geoff.


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

Chinese duplexers
 

Geoffrey S. Mendelson wrote:
Rob wrote:

No. There are two sides, one of them for the high frequency and the
other for the low frequency. The filter response is such that it passes
on one frequency and notches on the other.

Ok thanks. Note that they are tunable anywhere in the 136-17? range.

Assuming the pass side is set to pass 145.600 (the input) and the notch
side is set to notch out 145.000 (the output) and they are connected in
series, would that work?

It is not a pass side and a notch side. Both sides are pass/notch.

But on one side the pass freq is above the notch freq, and on the
other side the pass freq is below the notch freq.

On the Chinese duplexers you have found, the Q is probably not high
enough to tune the pass and notch to frequencies 600 kHz apart.

Chinese duplexers
 

Rob wrote:

On the Chinese duplexers you have found, the Q is probably not high
enough to tune the pass and notch to frequencies 600 kHz apart.

Ok, thanks.

Geoff.

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

Chinese duplexers
 

On 30 Aug 2011 13:01:01 GMT, Rob wrote:
Geoffrey S. Mendelson wrote:
Rob wrote:

No. There are two sides, one of them for the high frequency and the
other for the low frequency. The filter response is such that it passes
on one frequency and notches on the other.

Ok thanks. Note that they are tunable anywhere in the 136-17? range.

Assuming the pass side is set to pass 145.600 (the input) and the notch
side is set to notch out 145.000 (the output) and they are connected in
series, would that work?

It is not a pass side and a notch side. Both sides are pass/notch.

But on one side the pass freq is above the notch freq, and on the
other side the pass freq is below the notch freq.

On the Chinese duplexers you have found, the Q is probably not high
enough to tune the pass and notch to frequencies 600 kHz apart.

We still don't have a clear description of what the OP is trying to
accomplish.

Chinese duplexers
 

Allodoxaphobia wrote:

On 30 Aug 2011 13:01:01 GMT, Rob wrote:
Geoffrey S. Mendelson wrote:
Rob wrote:

No. There are two sides, one of them for the high frequency and the
other for the low frequency. The filter response is such that it passes
on one frequency and notches on the other.

Ok thanks. Note that they are tunable anywhere in the 136-17? range.

Assuming the pass side is set to pass 145.600 (the input) and the notch
side is set to notch out 145.000 (the output) and they are connected in
series, would that work?

It is not a pass side and a notch side. Both sides are pass/notch.

But on one side the pass freq is above the notch freq, and on the
other side the pass freq is below the notch freq.

On the Chinese duplexers you have found, the Q is probably not high
enough to tune the pass and notch to frequencies 600 kHz apart.

We still don't have a clear description of what the OP is trying to
accomplish.

He is wondering if something can be modified. He wants a half-duplex
radio with a 600 kHz split, on a common antenna. The duplexer he is
looking at has a 5 MHz offset. He wants to know if it can be
re-configured for ham with a much smaller offset.

http://www.repeater-builder.com/rbtip/2mduplexer.html

Chinese duplexers
 

Allodoxaphobia wrote:

We still don't have a clear description of what the OP is trying to
accomplish.

Take two radios, two j-poles and a lot of coax and make a repeater.
Obviously I will need some sort of controller in between but that's
irrelevant.

I want to place one J-pole (or similar antenna) at one corner of my garden,
and another at the other one (10 meters apart).

One will be used to receive a signal, the other to relay it. They both
will be somewhere on the 144-146mHz band, with the output being a few watts
with a max of 20.

Besides the distance, I was looking for a cheap way of not having
the transmitted signal block the receiver. The duplexer in question
is rated at 75dB isolation with a 3.5mHz split, I can only have .6 mHz.

What I was wondering is that since at a .6mHz split, the isolation will
be a lot less, can I somehow combine the two sides to make a better
filter?

Thanks,

Geoff.

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

Chinese duplexers
 

On Tue, 30 Aug 2011 11:44:03 +0000 (UTC), "Geoffrey S. Mendelson"
wrote:

I was looking at cheap HT's last night on eBay and I found several vendors
selling duplexers for repeater use. They sell for about $60 each.

They are 6 cavity (three transmit, three receive) and the closest they can
go on VHF is 3.5mHz.

Doing a web search I find they are not very good (what did you expect?)
but with a good front end they will work ok.

My problem is not only one of money (don't tell me to not waste my money
and buy a good, one, I can't afford it), but my 2m band is only 144-146
mHz, and the repeater portion is really just 145-146. I'm also limited
to 20w output.

So my question is anyone familar with them? Is it possible to take one
and convert it to a 6 cavity input filter? For example, I could put the
input on one side my yard and the output on the other, about 30 feet apart.

There are calculators that will predict the isolation. At 20 watts
(+43dBm), with a broadband synthesizer noise level at about -30dBm,
and an RX sensitivity of about -106dBm, you'll need at least 76dB of
TX-RX isolation. The little cavities have too wide a notch (i.e. low
Q) and will attentuate the RX signal and smoke the TX signal at 0.6Mhz
spacing. Seperating the antennas won't solve that problem. If you
try to get sufficient isolation using vertically isolated antennas,
you might get sufficient isolation, but the Q of the notch filters
will still kill the signal both ways.

Vertical antenna isolation:
http://awapps.commscope.com/products/bsa/_calculators/qvisolation.asp
Horizontal antenna isolation:
http://awapps.commscope.com/products/bsa/_calculators/qhisolation.asp

For example, if the input of the repeater was 145.600, could I have them
both tuned to 145.600 and connect the input of the receiver to one
set of cavities, the antenna to the other and leave the antenna connection
untouched, effectively placing them in series?

Nope. Not enough Q (too wide a notch).
Bigger cavities = higher Q.
More cavities = deeper notch and therefore more isolation.

Quiz: The Q of given cavity is 1000. If I critically couple 2 such
cavities in series, what is the resultant Q? 10 such cavities? etc?

Answer: 1000 in all cases. The 3dB bandwidth does not change when
tuned circuits are critically coupled.

Read the specs on the eBay web page. For example:
http://www.ebay.com/itm/110460354111
"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.


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

Chinese duplexers
 

On Tue, 30 Aug 2011 15:29:03 +0000 (UTC), "Geoffrey S. Mendelson"
wrote:

Allodoxaphobia wrote:

We still don't have a clear description of what the OP is trying to
accomplish.

Take two radios, two j-poles and a lot of coax and make a repeater.

Retch.

I want to place one J-pole (or similar antenna) at one corner of my garden,
and another at the other one (10 meters apart).

Plugging into:
http://awapps.commscope.com/products/bsa/_calculators/qhisolation.asp
I get about 30dB isolation (assuming 2dBi antenna gains).
The synthesizer noise belching from your xmitter is maybe -60dB down
from the +43dBm xmit carrier. That puts the noise level at -17dBm at
the receive antenna. Your receiver sensitivity is probably -106dBm,
which means you need about 90dB of isolation. The antenna spacing
will provide 30dB of that. You cavities are suppose to provide the
remaining 60dB of isolation. That's not going to happen with tiny
mobile duplexer cavities.

Hint1: You'll be close with vertical antenna isolation.
Hint2: Some radios have quite a bit of synthesizer noise, much of
which will be on your repeater receive frequency. This is why some
repeaters still use crystal oscillators instead of synthesizers.

One will be used to receive a signal, the other to relay it. They both
will be somewhere on the 144-146mHz band, with the output being a few watts
with a max of 20.

Somewhere? Duplexers are usually bench tuned to some specific
frequency. It's not a trivial exercise and requires some expenditures
in time and equipment. You can't easily move in frequency.

Besides the distance, I was looking for a cheap way of not having
the transmitted signal block the receiver. The duplexer in question
is rated at 75dB isolation with a 3.5mHz split, I can only have .6 mHz.

What I was wondering is that since at a .6mHz split, the isolation will
be a lot less, can I somehow combine the two sides to make a better
filter?

You can't improve things by simply adding more cavities. All you'll
do is add more loss:
Bigger cavities = higher Q and therefore closer frequency spacing.
More cavities = deeper notch and therefore more isolation.

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

Chinese duplexers
 

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.

Chinese duplexers
 

Jeff Liebermann wrote:
Take two radios, two j-poles and a lot of coax and make a repeater.

Retch.


Why? Don't you make experimental stuff? I did not say it was a permanent
repeater, it's actually a test bed for some repeater/internet linking
systems we are trying out.

Budget is zero, but I can swing a roll of rg-6 and maybe a $60 duplexer
if I don't buy anything else (radio/computer related) that month.

Plugging into:
http://awapps.commscope.com/products/bsa/_calculators/qhisolation.asp
I get about 30dB isolation (assuming 2dBi antenna gains).
The synthesizer noise belching from your xmitter is maybe -60dB down
from the +43dBm xmit carrier. That puts the noise level at -17dBm at
the receive antenna. Your receiver sensitivity is probably -106dBm,
which means you need about 90dB of isolation. The antenna spacing
will provide 30dB of that. You cavities are suppose to provide the
remaining 60dB of isolation. That's not going to happen with tiny
mobile duplexer cavities.

OK, thanks.


Hint1: You'll be close with vertical antenna isolation.

Explain, do you mean just the distance if they are both vertical, or
the distance AND one is vertical and the other horizontal?

Hint2: Some radios have quite a bit of synthesizer noise, much of
which will be on your repeater receive frequency. This is why some
repeaters still use crystal oscillators instead of synthesizers.

Also almost irrelevant. The radios wll be what I have, HTX-202s or what
I can scrounge (TBD). I'd love to get my hands on 2 channel Maxtracs
or similar radios out of taxis, but the people sitting on piles of them are
much more interesting in refurbishing and enhancing them than selling them
cheaply or giving them away.

I'd be very happy with ones that receive only or have blown finals that I
can get 2w or so out of.


One will be used to receive a signal, the other to relay it. They both
will be somewhere on the 144-146mHz band, with the output being a few watts
with a max of 20.

Somewhere? Duplexers are usually bench tuned to some specific
frequency. It's not a trivial exercise and requires some expenditures
in time and equipment. You can't easily move in frequency.

I know, but I don't have a "pair" yet. I'm not even sure there are any
available or a test one. So why be specific when I don't have that information
yet, and why wait for it to ask a technical question, which will have
the same answer no matter which frequencies I use?

You can't improve things by simply adding more cavities. All you'll
do is add more loss:
Bigger cavities = higher Q and therefore closer frequency spacing.
More cavities = deeper notch and therefore more isolation.

And that's the answer I need.

Thanks,

Geoff.

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

Chinese duplexers
 

On 8/30/2011 6:01 AM, Rob wrote:
Geoffrey S. wrote:
Rob wrote:

No. There are two sides, one of them for the high frequency and the
other for the low frequency. The filter response is such that it passes
on one frequency and notches on the other.

Ok thanks. Note that they are tunable anywhere in the 136-17? range.

Assuming the pass side is set to pass 145.600 (the input) and the notch
side is set to notch out 145.000 (the output) and they are connected in
series, would that work?

It is not a pass side and a notch side. Both sides are pass/notch.

But on one side the pass freq is above the notch freq, and on the
other side the pass freq is below the notch freq.

On the Chinese duplexers you have found, the Q is probably not high
enough to tune the pass and notch to frequencies 600 kHz apart.

one might be able to cascade two of them, but Rob's point about Q is
well taken.

It depends on whether the problem is the "depth of rejection" or the
"steepness of skirt". A single resonant unit has a narrow spike on top
of gentle shoulders. Say one section has Q of 1000 (i.e. the 3dB
bandwidth is 100kHz for 100MHz center frequency), but the rejection at 1
MHz away is only 20dB. I could cascade 3 sections, tuned exactly the
same, and I'd have 9dB loss at 100kHz, and 60dB rejection at 1 MHz away.
The 3dB bandwidth might be around 30kHz, or, you could stagger the
tuning slightly to get a little broader flat top, but keep the 60dB
(i.e. moving the center frequency of one cavity by 10kHz won't change
the attenuation at 101 MHz)

The design challenge is that you need to suppress the transmit signal
(at, say, 50W, +47dBm) low enough so that the front end of the receiver
can handle it without blocking (say, you want it down around -50dBm).
With our not so hot cavities described above, you'd need to stack up 5
sections at 20dB per section to get the 100dB suppression. Well, that's
not so great, because you probably now have a bunch of additional loss
in the receive path, AND you've got a real tuning chore on your hands to
make sure that all of them are tuned appropriately to get the required
bandwidth.

Enter the idea of a notch. Let's say our example is 101 MHz Tx and 100
MHz Rx. Rather than rely on the "far away" response of a resonator to
suppress the transmit, I can put a 101 MHz notch filter on the input to
my receiver. If I can get 30dB/section rejection, then 3 or 4 sections
will knock the Tx power down low enough to not block the receiver's
front end.

But wait, there's more... that Tx isn't a narrow spike. It has phase
noise sidebands that go out fairly far. Unfortunately, the run of the
mill transmitter might only suppress "off channel spurious and noise"
by, say, -50dBc (and a rig designed to operate half duplex is probably
worse). That means that your 50W (+47dBm) transmitter is putting out
-3dBm *at the receive frequency*, so no amount of filtering on the
receive path will help. Again, enter the notch filter.. you put a 100
MHz notch on the output of the transmitter.

Now.. as Rob points out, the Q might be kind of low. If the Q is, say,
100, then that 100MHz filter is 1MHz wide, and by the time you cascade
enough to get the BW down, the loss will be huge.


As you can see, this whole duplexer/diplexer/multicoupler design thing
can get pretty complex, and there's not usually a simple cookbook answer.

Chinese duplexers
 

On 8/30/2011 8:29 AM, Geoffrey S. Mendelson wrote:
Allodoxaphobia wrote:

We still don't have a clear description of what the OP is trying to
accomplish.

Take two radios, two j-poles and a lot of coax and make a repeater.
Obviously I will need some sort of controller in between but that's
irrelevant.

I want to place one J-pole (or similar antenna) at one corner of my garden,
and another at the other one (10 meters apart).


This will actually help a bit

The free space attenuation for 10 meters at 144MHz is
32.4+20*log10(0.01)+20*log10(144) 32.4-40 +43.2 = about 36dB.

If your Tx is 20W (+33dBm), then the receiver is going to see about
-3dBm at the Tx frequency. If you want to get the Tx signal down to
around -40dBm or so, you only need 30-40 dB of attenuation at the Tx freq

Then there's the Tx phase noise to worry about. Figure it's 60dB down,
so +33-60-36 = about -63dBm.. probably enough to completely mask any
received signals (what's your sensitivity.. -130dBM?) so you need a
notch with 70dB rejection on the output of your Tx.

You're 600kHz away, implying you need a Q better than a few hundred.
If you just tune up some of those cans for that, and the Q is too low,
then you'll be attenuating your transmitter.


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)

One will be used to receive a signal, the other to relay it. They both
will be somewhere on the 144-146mHz band, with the output being a few watts
with a max of 20.

Besides the distance, I was looking for a cheap way of not having
the transmitted signal block the receiver. The duplexer in question
is rated at 75dB isolation with a 3.5mHz split, I can only have .6 mHz.

What I was wondering is that since at a .6mHz split, the isolation will
be a lot less, can I somehow combine the two sides to make a better
filter?

Thanks,

Geoff.

Chinese duplexers
 

On Tue, 30 Aug 2011 16:29:03 +0000 (UTC), "Geoffrey S. Mendelson"
wrote:

Jeff Liebermann wrote:
Take two radios, two j-poles and a lot of coax and make a repeater.

Retch.

Why? Don't you make experimental stuff?

I don't like J-pole antennas. I've also built too many repeaters in
the past to know that they can't just be thrown together from
available parts. One of my friends learned that expensive lesson with
his 2m repeater. He started with two ham transceivers, went to two
Maxtrac radios, and finally to a GE MSTR II. Duplexers went from 4
cavity junk, to a 6 cavity monster.

I did not say it was a permanent
repeater, it's actually a test bed for some repeater/internet linking
systems we are trying out.

Sounds interesting. Plan on everything costing at least 4 times
what's predicted, and for things to take perhaps 4 times as long.
Unplanned repairs and "tweaks" should double the required time.

Budget is zero, but I can swing a roll of rg-6 and maybe a $60 duplexer
if I don't buy anything else (radio/computer related) that month.

Initial budget can be zero. Just plan on a replacement budget equal
to the price of a proper repeater.

How's this for an expensive mistake?
http://802.11junk.com/jeffl/K6BJ-MSF5000/
I've burned about $800 on this mess and it's still not on the air.
Wanna guess what went wrong? (Hint: it involves the internal
duplexer).

http://awapps.commscope.com/products/bsa/_calculators/qhisolation.asp

Hint1: You'll be close with vertical antenna isolation.

Explain, do you mean just the distance if they are both vertical, or
the distance AND one is vertical and the other horizontal?

Assuming vertically polarized monopole antennas, vertical isolation is
from tip of one antenna to the tip of the other antenna. Horizontal
isolation is just the horizontal spacing. If they're seperated both
vertically and horizontally, then there's a problem. You only need to
be offset horizontally slightly, for the antennas to couple. I ran
into this problem when I tried to put two vertically seperated
antennas on opposite sides of a tower. The isolation was better then
they were directly in line with each other, on the same side of the
tower. Incidentally, mounting one antenna upside down offers
additional distance and improved isolation.

Hint2: Some radios have quite a bit of synthesizer noise, much of
which will be on your repeater receive frequency. This is why some
repeaters still use crystal oscillators instead of synthesizers.

Also almost irrelevant. The radios wll be what I have, HTX-202s or what
I can scrounge (TBD).

Retch 2.0. Radio Shock HTX-202 handhelds tend to stick on the air
with low battery voltage. The receivers are also easily overloaded.
We have the remaining few HTX-202 radios used for APRS WX packet. I
would love to replace them, but nobody (including me) want's to spend
the time.

I'd love to get my hands on 2 channel Maxtracs
or similar radios out of taxis, but the people sitting on piles of them are
much more interesting in refurbishing and enhancing them than selling them
cheaply or giving them away.

Patience. On Jan 1, 2013, everything in the US is suppose to go
narrow band. There should be tons of cheap radios available on eBay
and from public safety outlets.

I'd be very happy with ones that receive only or have blown finals that I
can get 2w or so out of.

Make sure you get the ones with the 16 pin accessory connector. Many
of the Maxtrac's on eBay are actually cobbled together Radius or M120
radios, with odd boards and strange firmware. Caveat emptor.

I know, but I don't have a "pair" yet. I'm not even sure there are any
available or a test one. So why be specific when I don't have that information
yet, and why wait for it to ask a technical question, which will have
the same answer no matter which frequencies I use?

Careful. Some repeater frequencies are a problem. For example,
146.760 is on the 41st harmonic of the common 3.579545MHz clock osc
frequency. No problem at the repeater, but it will drive the users
nuts.

If co-located with other radios, be sure to do an intermodulation
study.
http://www3.telus.net/PassiveRF/
We found out too late that a mix of some of our transmit frequencies
lands on one of our inputs.

You can't improve things by simply adding more cavities. All you'll
do is add more loss:
Bigger cavities = higher Q and therefore closer frequency spacing.
More cavities = deeper notch and therefore more isolation.

And that's the answer I need.

You might find it easier to build a UHF repeater. With 5MHz spacing,
the cheap mobile duplexers will work with low power (25w) radios.

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

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)

Don't forget that in Region 1, the 2M band is only 2 MHz wide, the
bottom 500 kHz is dedicated to SSB and the top 200 kHz is for satellite.

Chinese duplexers
 

On 8/30/2011 11:14 AM, Rob wrote:
Jim 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)

Don't forget that in Region 1, the 2M band is only 2 MHz wide, the
bottom 500 kHz is dedicated to SSB and the top 200 kHz is for satellite.

Sure, that does make it harder. The OP is in region 2, though, where
there's 4 MHz theoretically available)

flame protective suit on And of course, a lot of the band plans are
basically gentlemen's agreements and have no force of law. As long as
you don't interfere with someone (challenging in some geographical
locations), you can pretty much do what you want.flame suit off

I wouldn't want to put input or output on 144.2, for instance.

But looking at the ARRL band plan, you could put your input up at
147.6-147.99 and put your output at 145.5-145.8 (Misc and experimental,
per ARRL).. not quite 3 MHz, but close, and a whole lot better than 600kHz.

Here in the Los Angeles area, either TASMA or the anti-TASMA folks would
probably round up people to have you tarred, feathered and run out of
town on a rail, no matter what you do. In any case, things move so
slowly that unless you were hideously inconsiderate and egregiously
interfering, you could probably run for a year or more before it would
get too nasty.

There is a 147.585/144.930 pair labeled for "portable repeater" in the
TASMA plan (max 72 hrs/month).. that's 2.5 MHz apart (to make filtering
easier). They also say 144.310-144.375 is for simplex unchannelized,
but I've not heard much on the air there..for an experiment, it would
probably work.

Chinese duplexers
 

"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"

Chinese duplexers
 

Jim Lux wrote:
On 8/30/2011 11:14 AM, Rob wrote:
Jim 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)

Don't forget that in Region 1, the 2M band is only 2 MHz wide, the
bottom 500 kHz is dedicated to SSB and the top 200 kHz is for satellite.

Sure, that does make it harder. The OP is in region 2, though, where
there's 4 MHz theoretically available)

I think he is in Region 1. He posts with 2 callsigns, one is a 4X1
(Israel) and mentions:

but my 2m band is only 144-146
mHz, and the repeater portion is really just 145-146.

flame protective suit on And of course, a lot of the band plans are
basically gentlemen's agreements and have no force of law. As long as
you don't interfere with someone (challenging in some geographical
locations), you can pretty much do what you want.flame suit off

Sure, but to get a permit for unattended operation, at least over here,
you'll need to abide to the band plans.

(in fact in my country, Netherlands, it is even worse: the repeater
frequencies are not coordinated by the ham community itself, but by
the equivalent of the FCC. they work strictly by a set of rules
originally drafted by the amateur societies, in the days the bands
were still overcrowded. arbitrary figures were put in those rules
regarding things like minimal desirable distance between repeaters,
maximum height of antennas, maximum EIRP power, that were originally
just there to regulate the inflow of new repeater projects a bit, so
everyone would have a fair chance of running a repeater. if you were
a few km too close, had an antenna a bit high, or similar, it usually
wasn't a problem. but one day an amateur who got refused a license
went to court claiming that others had gotten a license while not being
within the rules, and as a reaction the authority now strictly follows
the rules and refuses every application that does not fully conform to
all the rules. of course, operating on one of the reserved repeater
channels is one of the rules.)

Chinese duplexers
 

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.

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

Chinese duplexers
 

Geoffrey S. Mendelson wrote:

Allodoxaphobia wrote:

We still don't have a clear description of what the OP is trying to
accomplish.

Take two radios, two j-poles and a lot of coax and make a repeater.
Obviously I will need some sort of controller in between but that's
irrelevant.

I want to place one J-pole (or similar antenna) at one corner of my garden,
and another at the other one (10 meters apart).

One will be used to receive a signal, the other to relay it. They both
will be somewhere on the 144-146mHz band, with the output being a few watts
with a max of 20.

Besides the distance, I was looking for a cheap way of not having
the transmitted signal block the receiver. The duplexer in question
is rated at 75dB isolation with a 3.5mHz split, I can only have .6 mHz.

What I was wondering is that since at a .6mHz split, the isolation will
be a lot less, can I somehow combine the two sides to make a better
filter?

Thanks,

Geoff.


If you have two antennas you don't need a duplexer. Just notch the
transmit from the receive antenna.

Chinese duplexers
 

On 31 Aug 2011 12:41:25 GMT, dave wrote:

Geoffrey S. Mendelson wrote:

Allodoxaphobia wrote:

We still don't have a clear description of what the OP is trying to
accomplish.

Take two radios, two j-poles and a lot of coax and make a repeater.
Obviously I will need some sort of controller in between but that's
irrelevant.

I want to place one J-pole (or similar antenna) at one corner of my garden,
and another at the other one (10 meters apart).

One will be used to receive a signal, the other to relay it. They both
will be somewhere on the 144-146mHz band, with the output being a few watts
with a max of 20.

Besides the distance, I was looking for a cheap way of not having
the transmitted signal block the receiver. The duplexer in question
is rated at 75dB isolation with a 3.5mHz split, I can only have .6 mHz.

What I was wondering is that since at a .6mHz split, the isolation will
be a lot less, can I somehow combine the two sides to make a better
filter?

Thanks,

Geoff.


If you have two antennas you don't need a duplexer. Just notch the
transmit from the receive antenna.
I think that is what he is asking. Can he takes his duplexer and use
it as an extra sharp notch filter for his receiver. One "side" is
already set up for that purpose. He is asking if the "side"
originally intended for the transmitter can be used to further filter
the receiver.

Chinese duplexers
 

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

Chinese duplexers
 

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.

Chinese duplexers
 

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.

Chinese duplexers
 

Rob wrote:

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.

There is a limit of 100mW EIRP for 2400-2450 mHz for terrestrial use,
with a limit of 100W EIRP to satellites in the 2400-2402 mHz part of the
band. This is from a document on the Ministry of Communicatons website,
dated 1999. It has been unchanged except for the addition of 7.100-7.200 mHz
so they never bothered to update it.

The difference between a 100mW limit and an outright ban in practice is
very little IMHO.

For example, you can turn off encryption and use a WiFi device as a packet
radio, or you can call CQ on your cordless phone. :-(

Geoff.

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