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LukeH

Passive Repeater

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I like to hike in an area behind the mountains next to my academy/school/home. When I am back there I cannot reach the same repeaters that my friends can. Of course simplex will not work either. I was wondering...

 

What if... I took a high gain antenna, and put it on top of one of the hills between us, pointing at where my friends live. Then I would directly connect it to another antenna pointing to the other side of the hill, where I like to hike. My signals would be received by one antenna and sent to the other one to be retransmitted down the other side of the hill...

 

Is this something that could ever work? It seems possible but for some reason I have trouble believing that some inert pieces of metal on top of a mountain can magically allow me to communicate with someone on the other side of it.

 

But hey they sell those stick-on antenna enhancers for cell phones, that are little more than some scraps of foil, and people swear they work... who knows...

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Off topic, but those stick on cell phone antenna enhancers do not work in any way, aside from removing money from your wallet.

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The passive repeater (PR) works. It is all a matter of TX ERP, RX sensitivity, path loss, and PR loss. It is better with dishes and waveguides at microwave freqs. But it has been used at VHF.

 

I recommend using two yagis, and keep the cable between them short. It still may not work. But it is worth a try.

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Interesting. Do you think it might work better at 440 than 2m? That would also make a much smaller antenna to build.

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It is a trade-off. Antennas are smaller at 440, but path losses, coax and connector losses are greater. And as the gain of the antenna is increased, the beamwidth is decreased.

 

It can be done, but since I don't know the parameters of your system or needs, I cannot even begin to calculate if it will work for you.

 

Look in the "WHAT DO YOU USE" threads for my mention of using my mobile radio as a Cross-Band repeater. That might work for you. It gives me good repeater coverage while I patrol the canyons.

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If you want to give me the particulars of all the equipment I can calculate if it will work. I'll need: Tx power, Rx sens, distance between stations and repeater, gain of antennas at repeater, coaxial cable types and lengths to calculate loss. Yeah, that should do it. As with all calculation, the more accurate the information going in, the more accurate the result.

 

I've done this for microwave systems a few times. :-)

 

CA

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I don't have all the equipment yet as it is really just speculation, but here's what info I can give. I use a 5W HT on which I traded the rubber duck antenna for a 1/4 wave vertical. Since it's on an HT the antenna performance can obviously change dramatically depending on its orientation and the ground type, from between -1 to +3 dBi, so I really don't know what figure to give for HT antenna gain. My RX sens is 0.18 microvolt at 12 dB sinad on 440, and 0.16 microvolt on 2m. Let's assume for now the guys at the other end have a similar tx/rx setup.

 

The passive repeater would be located on a hilltop with direct LOS to both me and my friends, and would be about 2.5 km from them whereas I would be between 2 and 10 km from it. I don't have the antennas, but perhaps the math can be done to determine how much gain they would need to have if this were to work. I would use only a little bit of cable between them... perhaps about 3-6 feet of 9913.

 

Of course a crossband repeater would easily do what I need, and I'll probably play around with that in the near future.

 

Thanks for the replies though. It's interesting just trying to see if this might work, regardless of whether I actually get around to testing it.

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