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Passive Repeaters




 
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ka1tdq
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« Reply #25 on: July 26, 2018, 08:45:55 PM »

I just finished building an even bigger one! 100 feet of LDF4 coax with two UHF verticals and a Yagi pointed at the radio master site.

Yeah, it still doesnít work. I think itís a matter of critical mass that we havenít hit yet. Maybe phased arrays?

Jon
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KF7WWW
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« Reply #26 on: July 26, 2018, 09:33:09 PM »

Time to stop playing in the amateur world and go to the professional world. Cheap fast solutions arenít going to get you anywhere. You want converage inside a building. Get the city to pony up and contact EMR. If you donít want to handle it yourself. PM me. I can put you in contact with the people that can make it happen.
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Patrick J. / KD5OEI
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« Reply #27 on: July 28, 2018, 09:08:44 AM »

What you are trying, passive repeater, helps when a totally enclosed metal building is the problem and the frequencies are UHF+. On a cellphone, made the difference of the phone ringing and no one there, to the connection actually going through. The coaxial cable was nothing special but only 1 FT long. No idolatry was employed.
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ka1tdq
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« Reply #28 on: July 28, 2018, 11:11:48 AM »

That's the problem I see.  Everything on the web relating to passive repeaters is anecdotal.  I haven't found any industry or government studies on the subject, but rather someone's story saying, "It works."  This is my fourth time dealing with this issue, and not once has it worked.  Using a spectrum analyzer, I see no increase in signal strength.  Certainly if it were sound science, wouldn't MFJ have a product for it by now?  They have a knick knack for everything. 

Every time I mention that these don't work, or joke that they're voodoo technology, it's as though I'm insulting someone's religion (which is in itself a series of anecdotes). 

Jon
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Patrick J. / KD5OEI
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« Reply #29 on: August 01, 2018, 10:21:43 PM »

I believe I am lucky and nothing else. No science was used therefore I can't possibly be insulted.

The people in charge who want their serious radios to work need to cough up some $, pay someone, and use commercial guaranteed-to-work stuff that runs off 120V outlets.

I am astonished that you actually went as far as using 100' of coax. any coax.
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Radio Candelstein - Flagship Station of the NRK Radio Network.
ka1tdq
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« Reply #30 on: August 02, 2018, 12:00:56 AM »

I just performed a test, by accident yesterday.  I brought in a 9-element quad antenna that I want to experiment with for satellites, and among the tests I did was a front/back ratio test.  I put a signal generator on 437 MHz at -50db on my desk with a little UHF vertical antenna.  I then stood 10' away with my quad plugged into an Anritsu spectrum analyzer.  

Pointing my quad directly at the antenna, received signal was -82dbm and 180 degrees away was -97dbm.

Coincidentally, one of the readings from the passive repeater test that I installed was that the incoming master site signal which was -50dbm, from the yagi mounted outside. Again, this signal was supposed to passively repeat by the little UHF vertical antenna which it was connected to inside the building.

To use the numbers that I used at my bench with my homebrew satellite antenna, an end user in the building would need to point a 9-element quad 10 feet away directly at that little antenna to get a -82dbm signal.  From my measurements in the room without the passive repeater, background signal alone from the radio master site was -78dbm.

I then plugged in the passive repeater and found absolutely no difference in background room signal strength (obviously, because I didn't have a moon bounce array of beams pointed at that little UHF vertical antenna).

Jon


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Jim, W5JO
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« Reply #31 on: August 02, 2018, 09:02:33 AM »

If you are expecting to see gain through the antennas, it won't be there.  From what I read that is what you are looking for.  You will see the same signal level at the output minus the losses of the coax and connectors that you put in on the other end.
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Jim/WA2MER
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« Reply #32 on: August 02, 2018, 12:47:50 PM »

The entire premise of passive repeaters that are intended to provide indoor coverage is to reduce the effect of building losses enough so that the net signal into the building is enough to provide reliable communications. You don't need to get the same level indoors as you have outdoors, you need only get enough signal to meet your performance requirements.

For example, let's say you have a radio with a working sensitivity of -120 dBm, and you want a 10 dB margin to account for a fading environment, so your design threshold sensitivity is -110 dBm. Your building presents a 30 dB loss to the desired signal. The outdoor signal at the location of where you would install the donor antenna is -95 dBm, not strong enough to set your hair on fire but plenty strong enough for outdoor coverage with 15 dB over your design margin. However, the signal inside your -30 dB building would be only -125 dBm, so you're now below the radio's working sensitivity and you can't communicate reliably, if at all. But if you select a pair of antennas and cable such that the resulting loss through your passive system is less than 15 dB you're gold, but only right at the location of the indoor antenna. The indoor signal level will fall off rapidly due to free space loss, and losses presented by indoor obstructions like walls and such.

Passive repeaters can work, but as you can see they have very, very limited applications and generally cover small indoor spaces. They are not fantasy, but they fail because they're seldom the right choice for the application. In today's marketplace with the availability of small and relatively low cost BDAs, active devices are definitely the way to go. You just have to choose one wisely, one that will not only provide sufficient gain, but one that will work in your particular RF environment (overload and interference from unwanted signals, etc.).
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Anything worth doing is worth doing to excess.
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ka1tdq
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« Reply #33 on: August 05, 2018, 03:36:09 PM »

Exactly. You can pay your tithes, but you'll probably get more bang for your buck going to Las Vegas.

Jon
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KF7WWW
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« Reply #34 on: August 05, 2018, 08:06:10 PM »

Jon
Contact Procomm. Heís one of your Kenwood dealers.
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Steve - K4HX
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« Reply #35 on: August 06, 2018, 12:01:52 PM »

Such things have been around for the cell bands for years. An amplifier is always in the mix though to amplify the received signal and provide isolation between the input and outputs. Wilson makes some pretty good one. Should be able to do the same with your freq/requirement.
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