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Author Topic: Repeater antenna as passive repeater?  (Read 735 times)
KX4QP
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Posts: 287




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« on: May 19, 2019, 07:38:49 AM »

I've been going around and around concerning trying to reach a repeater that's blocked by roundly a thousand feet of a mountain.  I've gotten dozens of suggestions ranging from "you need more power" to "put a Yagi on a mast and hook up your HT and you'll be fine".

One of those suggestions was to put a passive repeater on the intervening ridge, then aim a Yagi at that.  I rejected that at first, because all the land on the ridge is privately owned and fenced in (due to past history of hang gliders getting hurt flying off the mountain).  However, something else occurred to me in that regard.

As I understand it, what's been referred to as a "passive repeater" is nothing more or less than a half wave antenna, which will re-radiate (with some loss) any signal close to its resonant frequency.  The loss is fairly high, but the radiation is omnidirectional, meaning it ought to reach down into the signal shadow from the mountain.  And while I can't get up there to plant a pole with a meter of copper tube on it (or equivalent), I might not have to, because several others already have.

There are four repeaters already on that ridge (none of them connect to the group I want to access, however).  If I aim a signal at one of those repeaters, its antenna ought to re-radiate as a passive, as long as the signal I send is well separated from the receive and transmit frequency of attached repeater -- and that qualification is assured, because I'd be sending on the frequency for a different repeater.  The one I want to reach is on 146.865; one I use regularly up there is 145.470.

I already know this doesn't work with the antenna I have on my HT, but I should be able to get close to double the signal with a Yagi (3 dB over a short whip isn't a huge gain for a beam antenna).

My HT has plenty of power to key a repeater at the distance involved, if I have clear line of sight -- there's one I've worked from hilltops near home, at a distance of forty miles, which is 500 or so feet up a TV tower.  What I don't know is whether the loss on a passive will be too much to reach a repeater at thirty miles after re-radiation -- or whether an antenna with a repeater attached will even work as a passive on a different frequency.
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W9IQ
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« Reply #1 on: May 19, 2019, 07:51:09 AM »

Unfortunately what you propose will probably not work. The antennas that are already on that site are terminated by receivers on the repeaters, etc. This termination largely absorbs any in-band signal received by the repeater antenna so no re-radiation occurs.

You might, however, be fortunate enough that there is sufficient metals structures so as to cause your signal to be sufficiently scattered so as to hit the desired repeater. This may require more directed power to be effective.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
W9IQ
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Posts: 2903




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« Reply #2 on: May 19, 2019, 08:17:32 AM »

I should mention that you can build a moderately high gain yagi antenna from some copper wire and a piece of wood. It may not hold up to long term weather exposure but it is an inexpensive and quick way to test if more directed power would hit the repeater. You should easily be able to obtain a 10+ dBi gain with a day's worth of work and $20 worth of materials - plus you learn a lot from the experience.

25 feet of 8 gauge copper wire, an 8 foot piece of pine 1 x 2 and coax of a length to suit and you are in business for making a six element, wide spaced Yagi.

- Glenn W9IQ

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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
K5LXP
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« Reply #3 on: May 20, 2019, 04:38:41 AM »


My one experience with a passive repeater was when I was a kid my hamshack was on the 2nd floor but I often did projects in the basement workshop.  I could barely hear the club repeater with my HT in the basement and there was no way I was getting in.  I had a homebrew 5 element 2M yagi on a TV rotor for my hamshack and I heard about passive repeaters and thought I'd give it a shot.  I ran some coax down a heating duct, connected it to a mag mount in the basement and connected the coax from the yagi to the basement coax.  Pointed the yagi towards the repeater and what was a barely readable signal before was now full quieting, and I could easily access the repeater from the basement.  Of course I could've just connected the yagi coax directly to the radio and get all the gain in the world but it still worked very well via the mag mount link.

The upshot of this though is even with the gains involved there isn't a lot of signal to be recovered and reradiated.  You could probably crunch the numbers and figure out what the line of sight signal levels would be making various assumptions but I don't think that will be enough to get you over the hill.

Now, another point to consider is a remote base or link.  A cross-band repeater or similar in a favorable location would work like a hose.  That assumes you have access to that favorable location but a friend or relative that lives in the right spot would check the box.

Mark K5LXP
Albuquerque, NM
 
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K4JJL
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« Reply #4 on: May 20, 2019, 05:55:06 AM »

I put one of those in years ago for GA Power.  It wasn't a long distance solution, though.  It was so that they could get their VHF repeater signal underground in the coal conveyor tunnels.  One end was a high gain Yagi precisely pointed at the repeater antenna.  From there we ran 1/2" heliax down to the tunnel where it was changed to 1/2" radiax (leaky heliax w/ the shield ground off to let the signal out).  This was terminated w/ a 1/4 wavelength mag mount antenna 1/2 mile underground.  Worked great on high band.  Too lossy on higher frequencies to work.  The loss in radiax at UHF frequencies was awful.
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KX4QP
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Posts: 287




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« Reply #5 on: May 20, 2019, 03:45:48 PM »

I should mention that you can build a moderately high gain yagi antenna from some copper wire and a piece of wood. It may not hold up to long term weather exposure but it is an inexpensive and quick way to test if more directed power would hit the repeater. You should easily be able to obtain a 10+ dBi gain with a day's worth of work and $20 worth of materials - plus you learn a lot from the experience.

25 feet of 8 gauge copper wire, an 8 foot piece of pine 1 x 2 and coax of a length to suit and you are in business for making a six element, wide spaced Yagi.

- Glenn W9IQ



If/when I build one of these, I'm more likely to use PVC or ABS pipe; glue the copper into holes drilled through (except the radiator, which needs an insulating gap) and it'll hold up for years even if left up in the sun.  I might also sub 1/4" soft copper tube, as it's easier to work than 8 ga. solid wire and still fairly cheap.  Reflection preserves polarization, as I recall (meaning I need the radiator vertical).  Does scatter do the same, or randomize it?
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KC0UKR
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« Reply #6 on: May 20, 2019, 04:44:03 PM »

Am I wrong or have you still not simply even tried using a full power mobile rig and antenna from your house yet?

All of this jacking around and you will not try just the obvious thing first?
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W9IQ
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« Reply #7 on: May 20, 2019, 08:13:25 PM »

Quote
Does scatter do the same, or randomize it?

It will generally produce a random pattern.

Can you hear this repeater but are simply unable to key it up?

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
KX4QP
Member

Posts: 287




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« Reply #8 on: May 21, 2019, 04:24:23 PM »

Quote
Does scatter do the same, or randomize it?

It will generally produce a random pattern.

Can you hear this repeater but are simply unable to key it up?

- Glenn W9IQ

I've never heard it, but I haven't spent hours listening for it, either.

And no, @KC0UKR, I haven't had a chance to try a full power mobile from my home yet.  Are you volunteering?  I thought not. 
Quote
All of this jacking around and you will not try just the obvious thing first?
  It would be obvious, if I had access to such a rig.  I live an hour from the center of my club's membership.  I don't see trying to get someone to drive two hours (one each way) for a five minute test.
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KC0UKR
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Posts: 46




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« Reply #9 on: May 21, 2019, 06:48:15 PM »

I would be thrilled to help if I could,I still have no clue where you are though?

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KA5IPF
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« Reply #10 on: May 22, 2019, 05:46:43 AM »

Quote
Does scatter do the same, or randomize it?

It will generally produce a random pattern.

Can you hear this repeater but are simply unable to key it up?

- Glenn W9IQ

I've never heard it, but I haven't spent hours listening for it, either.

And no, @KC0UKR, I haven't had a chance to try a full power mobile from my home yet.  Are you volunteering?  I thought not. 
Quote
All of this jacking around and you will not try just the obvious thing first?
  It would be obvious, if I had access to such a rig.  I live an hour from the center of my club's membership.  I don't see trying to get someone to drive two hours (one each way) for a five minute test.

Maybe ask the club if they have a loaner, most do or at least have a member willing to loan a radio to a newbie. Quit kevtchin' and start doing.
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KX4QP
Member

Posts: 287




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« Reply #11 on: May 22, 2019, 04:29:10 PM »

I would be thrilled to help if I could,I still have no clue where you are though?



Pretty sure the FCC will show my address to anyone who enters my call, and Google Maps shows my house with my partner's car parked outside (must have taken the "satellite" photo while I was at work).

I'm in north central North Carolina, on the borderline between Sauratown and Poplar Flats (my mailing address is in King, but I'm outside that town limit).  If you find Sauratown Mountain on a repeater map, that's the one that's directly between me and the repeater in Fancy Gap, VA that connects to my club.  My grid location is EM96ui, near the southwest corner of that square.

My club is centered in Thomasville, about an hour's drive south.  There isn't a club (that I've found) near here, say in Pilot Mountain or Mount Airy or Danbury or Walnut Cove.  The next closer one (in Winston-Salem) meets after my bedtime on Monday nights; the one I attend meets on Saturday mornings, once a month.  One member provides a "club shack" with rigs, antennae, refreshments, and cameraderie -- once again, open only late enough to seriously compromise my sleep schedule.  I could reasonably check in on the club net, however, if I could reach one of their repeaters.  Not having an hour drive to get to bed after staying up too late is a huge advantage.

And no, I have no interest in trying to organize a new club; I did that once with model rockets back in the 1990s, and once was enough.  I'd join a local one if someone organizes it, however.
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KX4QP
Member

Posts: 287




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« Reply #12 on: May 22, 2019, 04:33:37 PM »

Maybe ask the club if they have a loaner, most do or at least have a member willing to loan a radio to a newbie. Quit kevtchin' and start doing.

I do plan to get a 65W mobile to install in my car, when the budget permits.  Tax refund went on completing another (already ongoing) project, and the budget's been tight for a couple months between.  Should be able to get that (bought and installed) no later than end of July.
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KC0UKR
Member

Posts: 46




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« Reply #13 on: May 23, 2019, 05:38:29 AM »

Sorry I guess I don't know what I was thinking asking for your location,I assure you this will not happen again.

Ignored,Troll.

I would be thrilled to help if I could,I still have no clue where you are though?



Pretty sure the FCC will show my address to anyone who enters my call, and Google Maps shows my house with my partner's car parked outside (must have taken the "satellite" photo while I was at work).

I'm in north central North Carolina, on the borderline between Sauratown and Poplar Flats (my mailing address is in King, but I'm outside that town limit).  If you find Sauratown Mountain on a repeater map, that's the one that's directly between me and the repeater in Fancy Gap, VA that connects to my club.  My grid location is EM96ui, near the southwest corner of that square.

My club is centered in Thomasville, about an hour's drive south.  There isn't a club (that I've found) near here, say in Pilot Mountain or Mount Airy or Danbury or Walnut Cove.  The next closer one (in Winston-Salem) meets after my bedtime on Monday nights; the one I attend meets on Saturday mornings, once a month.  One member provides a "club shack" with rigs, antennae, refreshments, and cameraderie -- once again, open only late enough to seriously compromise my sleep schedule.  I could reasonably check in on the club net, however, if I could reach one of their repeaters.  Not having an hour drive to get to bed after staying up too late is a huge advantage.

And no, I have no interest in trying to organize a new club; I did that once with model rockets back in the 1990s, and once was enough.  I'd join a local one if someone organizes it, however.
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KX4QP
Member

Posts: 287




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« Reply #14 on: May 23, 2019, 03:26:06 PM »

Okay, would someone who isn't on a high horse like to explain how giving everything about my location except a street address makes me a troll?  Or, alternately, how can I tell which three members of eHam not to ignore myself...
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