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Author Topic: 2M repeater tuned cavitys or 2 antennas  (Read 26035 times)
K1ZJH
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Posts: 901




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« Reply #15 on: November 15, 2011, 07:02:18 AM »

Weren't those fun days???  Grin

Our club officiers would get calls all times of the day whenever the repeater burped.

Pete
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AE6ZW
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« Reply #16 on: November 25, 2011, 09:39:36 PM »

I have helped set up repeaters once around 1999,  I found a 4 cavity  5 or 6 inch diameter  duplexer on ebay for around $400, but it did not come with phasing cable, so I made one, I made it so each connection to next cavity is electrical 1/4 wave , I used network analyzer to do it, since cavity itself has some electrical length, also cavity's coupling was too tight ( low loss, but not enough notch ), so I had to make coupling loop smaller to have more loss but looser coupling to do 600 khz separation.  after that I got about 85 dB isolation from TX to RX,  a little bit lower iso from RX to TX.
loss of filter on TX and RX path were about 3 dB  ( typical ? )     today I think something like MFJ 259B   can measure electrical length of cable, and since it work like one port network analyzer, it probably able to tune duplexer with a little patient.  I learned a lot about duplexer and cavity with this experience,
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K1ZJH
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« Reply #17 on: December 25, 2011, 08:39:16 PM »

I got started in repeaters back in the late 60s, long before it was commercially exploited or
popular.  Having a job as a transmitter engineer  at a major TV station, with a sympathetic
chief engineer who was also a ham, on a very tall mountain in Holyoke,  MA helped a bit Smiley
Some of the first users were OTs using converted 2mtr Gooney Birds and slope detection. You
couldn't buy repeaters, controllers or synthesized rigs. I was using a RCA mobile with
a dynamotor that would such a car battery dead in 3 minutes Smiley  Our  machines used Sinclair
hybird ring duplexers could reach well over 100dB isolation between ports. I think the
repeaters I was involved in are probably still using them some of those Sinclairs forty years later.
Everything was hand built, scrounged, or converted from retired FM commercial radios.

FM rpts were on the cutting edge back in those days. Today any fool with deep pockets can
pay the money and go plug and play. The magic is long gone, as are many of the pioneers who
are now silent keys.

Pete
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K7LZR
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Posts: 25




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« Reply #18 on: March 19, 2012, 10:16:50 PM »


FM rpts were on the cutting edge back in those days. Today any fool with deep pockets can
pay the money and go plug and play. The magic is long gone, as are many of the pioneers who
are now silent keys.

Pete

So true I'm afraid Sad
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NK7J
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Posts: 11




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« Reply #19 on: June 19, 2012, 02:37:10 PM »


One more suggestion is to use "retired" commercial equipment.  IMO it will outperform all of the brand new HAM repeaters for a whole lot less money.  All of my repeaters are GE Mastr II's.  The 100 watt continuous duty models can be had for around $200.  It takes a bit of knowledge to get them up and running on the ham bands, but they do not have to be modified - just retuned. 



Dick  AD4U

I agree some of the commercial stuff is the way to go, I personally have 3 Master II repeaters up, they just keep ticking. With one caveat, get the older style control racks, with the separate control cards. Back in the late 80s early 90s GE came out with the new and improved master II with the all in one control board made by IDA corp.... If you find one of those get it for free, then spend some time ditching the IDA board and installing a real controller. If you have to give more than $.01 for it run away.

As far as Antennas/Duplexers I agree with most of the comments that it is just plain easier and more cost effective to put in a good set of cans. Another point is get a good antenna, dont do what a lot of hams do when they go by a commercial shop and pick up our take downs... There is a reason we took them down, and most are cut for another freq and will not tune well at all in the ham band, the one notable exception is some of the folded dipoles that are wide band (like from 138-174mhz). Again if they are laying against the side of a shop there is a reason, sometimes you can get lucky though and pick up one that you can rebuild cheaply.
Also dont go buy a diamond antenna and expect it to last more than a few months to a year up on a mountain.
Have fun. If you need a set of good cans let me know, I have 5 sets sitting out in the shop that I would part with.
73
Jack NK7J   
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AF6D
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« Reply #20 on: July 01, 2012, 05:15:47 AM »

This is an older thread but timely for me.

I am moving my 2 meter machine from my home at 6,400 feet in the mountains to Heap's Peak. Heap's Peak is DIRTY. I am told that the only way to get a decent system is split antennas and a duplexer. 3 cavities on RX and 3 cavities on TX. Because of 74kW FM transmitter next to my tower the TX antenna would be up top and the RX antenna would be below. I don't know the spacing that is required but both antennas are DB224e's.

Respectfully, could you tell me what is so difficult in this? I must be missing something. As far as a balanced system turn the TX power down?

Heap's is gonna be a sonna-mo-beach but besides covering all of So. Calif. on the metropolitan side it covers all of the desert as well. Advice on this particular site are welcomed. I plan on using a WaCom WP-642 BpBr. I currently have the repeater on a Sinclair Res-Lok but the cable harness doesn't use a T at the end. Besides, I think the 8" cavities will be better suited on such a noisy site. I am one mile away listening to another repeater and my 5 watt HT can barely be heard. I don't want that! I'll stay here and give up 1/2 of the desert if I have to.

Can you tell me what I need to do to make split antennas and a duplexer work? I also have a two cavity Chip Angle with a 17dB preamp. Does it go in front of the duplexer or behind? It's 1MHz window would put a cleaner signal into the duplexers.

@Steve, I haven't heard you on HF in awhile.

Bob - AF6D
147.705 ( - ) 167.9

Everything's possible but getting a repeater to function well using split antennas instead of a duplexer is pretty hard and takes experience and experimentation.

It almost always creates an "unbalanced" system, since one antenna will be higher than the other.  To get enough spacing on 2m to make this work, one antenna would normally be about 100 feet higher than the other.  If that's the TX antenna, the repeater will get out a lot farther than it can hear; if it's the RX antenna on top, it will hear better than it gets out.

One way this can work pretty well is "split site," where the separation is quite far (can be a mile or more) and the RX signal is linked back to the TX site via a higher frequency ham band link, or via telephone, or via the internet.  That almost always results in an "unbalanced" system, but at least it works, and you don't run into desensitization and noise issues.

A duplexer's a lot easier and only requires one antenna and one transmission line.  When one considers how much good antennas and coax cost, that savings could be invested in a duplexer to have a better system for not much more money -- in some cases, maybe even less money.
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K1ZJH
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Posts: 901




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« Reply #21 on: July 01, 2012, 06:27:16 AM »

If you are running seperate antennas and a split duplexer, chances are you won't run
into an unbalance in the receive and transmitter coverage patterns.  That usually
happens at sites where the receiver and transmitter antennas have to be separated
by several feet to obtain reasonable isolation.

The size of the duplexer cavities, and the number of cavities doesn't mean squat.
The best duplexers I ever used were hybrid ring Sinclairs, dating back to the late
1960s or so... four cavities, but they could develop a notch that was over 110 dB
down! Some newer duplexer designs are BP-BR, which offer better out of band rejection.
We had to run with separate antennas and a split duplexer for years on Mt. Tom
due to a problematic 153 MHz Telco IMTS system that shared the site.  One comment,
if the site is dirty, and if there is garbage on the repeater input, no amount of filtering
will get rid of on channel garbage.

Pete
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AF6D
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Posts: 215


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« Reply #22 on: July 01, 2012, 02:30:35 PM »

I can I tell if there is garbage on the input when there is garbage all around? My Chip Angle should kill much of the noise right off the bat. Splitting the antennas and duplexer should cover the cavities, right?
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