Author Topic: "Nacho" Antenna  (Read 2337 times)

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SigInt

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"Nacho" Antenna
« on: March 25, 2012, 09:02:45 PM »
This post is in reference to a conversation that PLA and myself had about Passive Repeaters and how to resolve a problem he has seeing around a mountain.

He mentioned it and I started spouting my mouth off about it should work and in theory it should...

Until you want to use it to transmit.

My brain had wandered back to the Bill Cheek days of scanning radio and I remember a discussion about how a passiver repeaters worked. I had actually made one work once with a disk type kids sled. I had mounted it on a tree and used it as a reflector of sorts. I was actually able to pick up some frequencies that I was otherwise unable to reach as I found that the sweet spot was very tiny.

PLA and I had talked about taking a couple of high gain antennas and I started some research on it an could not find anything that supported what I was talking about and the reason why was I had not considered the fact that PLA would like to transmit on it.

I brought the question to a group of very knowledgable hams that included a gentleman that built many devices for the military and another very qualified FCC commercially licensed engineer as to if a passive repeater would work and the what t would take to make it work. The conversation was very interesting and I wish that I could have recorded it but I was on the road at the time. The best part or the worst part depending if you were me at the time came after I had when into the cubical farm and I had to turn the HT off.

THe FCC guru said it would not work but I could not hear everything so the next time I got a chance I emailed him about what he was saying when I had to turn off the HT and the following came from him...

Quote
ANT to ANT with low power? Give it up
.
Now, if you had a KW down in a hole with 15 dB gain antennas pointed at each other, you would have an ERP gain of 1,024,000 watts.(1kw x2x2x2x2x2= 32kwERP and the RX antenna has 32kw x2x2x2x2x2=1024 KW ERP). Sounds like a lot, but it is the separation that kills you. Of the 1 KW you might have a lot of gain, but 32 x 0 is still 0. So there is still little of the 1KW getting to your antenna, most, 99.9999 is lost. If you where a few feet apart, that would be different. But if you had a high gain pointing to another high gain on a hill, then coupled to another high gain pointed 50 miles to another high gain antenna, maybe it would work "one way". You would need the KW on the way back. It is all a numbers game. Figure the ERP out, then the signal you will introduce into another antenna, then out that antenna to the next one. You add up all the losses and gains and you have what you have. It all depends on how close the antennas (and therefore loss) are. (And you do know you can not put out more than 50 watts on UHF, right? :))

Now I am not sure where he wants to shoot to, but from Nacho you can not hit any repeaters up here in Tucson, not any down in town well even from top of Mule, maybe a little into Lemmon with power, but not all that well.

We hop from Lemmon to Sonoita to Mule. If you were on Mule, and you pointed up there and pointed the other one to Lemmon, you might get a few 100 microvolts  into the first ant, and out the other antenna. But park your car on Mule and run 1/1000 of a watt and see how it works. Almost all your power is lost getting to the first antenna, there is no power to feed the 2nd antenna, without an amp.

What he would need is a repeater, and that is very doable. I have made many for customers in the past. It hears you and retransmits to the input to the 100 mile away repeater, using 20 or more watts. and it hears the far away RPT and like wise transmits down in the "hole" to you. I linked Mule to Keystone years ago. Very doable, and very costly.

Microwave can do it in the gigs with very large (over kill) antennas and a reflector that at your frequency would be huge. A 50' x 50' reflector at 23 Ghz would be 2500 1/2 waves wide! At 146 that 50x50 reflector would need to be 1.5 miles tall and 1.5 miles wide for the same gain. As you can see, you can do on microwave what you can not do on VHF, or even UHF. You should see what the Russians built! an over the horizon radar that was huge, and had millions and millions of watts ran to it.

I think you start to see the problem... With a KW or more you can get on 220 and communicate with data burst using  falling meteorites from the ionized tails. You can also do this on 10 meters, I sure to do it for 400 mile skip. I had a KW and a 40 foot long 8 element "Super Lazier 500" cut to 10 meters


Long story short is that in order to get that transmitted signal around the corner you will need ONE big receiving antenna to act as a signal multiplier.

From PLA's point of view it looks like he probably has the situation resolved for now using  a crossband repeater.

A couple of other resolutions popped up and one of them came from the president of the Club here in the Tucson metro area. He suggested making  a simplex leg from the Bisbee "Nacho" area  and as long as the site (PLAs QTH) can support a static external class IP address. With this static address the controller here in the Tucson area will pump the voice to PLA's QTH (a small amount of data - probably around 35Kbits to maintain a decent sounding voice at the NACHO side and in to the repeater network here in Tucson. Then anytime someone uses the repeater here it will end up in NACHOLAND.

Yes this will require another radio and depending on the the requirements and terrain you would put in an antenna that would give the coverage and range that would be desired for the area.

The cool thing is (if you care) it is expected that when this next repeater goes in the actual coverage will be over 20,000 square miles of Southern Arizona, south of Picacho Peak as far west as Sells (on a good day) about 100 miles into Mexico and then coverage into the Benson area and PERHAPS NACHOLAND and Bisbee. The great thing about this network is it has a very reliable ECHOLINK setup that will allow access to the rest of the world.

This would mean that very likely that PLA could reach all of the Tucson Metro area and south with an HT while not using DTMF and the world using DTMF.

The other option would be to set up a SYSOP ECHOLINK/Radio arrangement and bridge his (PLA's) connection via the IP. This dos not require a static IP address all of the same variables apply though.

PLA send me a PM and I have been asked to invite you to the repeaters the Guru owns in the area that serve where you live. I will give you the technicalities.
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spacecase0

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Re: "Nacho" Antenna
« Reply #1 on: March 25, 2012, 10:23:28 PM »
I bounce signals off of trees all the time,
that seems less efficient than the passive repeater,
but a group of trees is bigger...
now I want to run tests

you only need about 0.2 microvolts at the repeater antenna (maybe more if it is an older system),
so it is not like you can't loose most of it,
the quoted math did not seem to point that out.

SigInt

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Re: "Nacho" Antenna
« Reply #2 on: March 25, 2012, 11:36:51 PM »
There is a buttload of mining in AZ and out here they have billboard sized passive repeaters above the mine to get RF in and out of the mine. You can also do some pool shots off of some of the mountains. His point was based on XMIT efficiency.

As far as RCV goes I have used all kinds of things, cars refrigerators, people, A concrete pad (steel reenforcement).

I wonder how efficient water is as a reflector. I am guessing water is the reflector in the case of trees.

I guess We have a pretty good place out here to do that testing with as there is a fairly flat piece of ground with very little in front of it except for an area that has a "grove?" of pecan trees. It would be interesting to see the energy reflected back from the trees when compared to the same energy not reflected, energy sent directly and and the energy reflected using a piece of sheet metal as a baseline of some sort.

Do you have a scope? The radios I would love to use for the test are Spread Spectrum as they would tend to ignore the differences in the noise flore from day to day. But they have no meters :(
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Earth Abides
The Road
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Hamsexy

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Re: "Nacho" Antenna
« Reply #3 on: March 26, 2012, 04:55:45 AM »
There is a buttload of mining in AZ and out here they have billboard sized passive repeaters above the mine to get RF in and out of the mine. You can also do some pool shots off of some of the mountains.

You might enjoy reading about KQ6XA.  She has done a lot of deep cave radio comms and developed her own antennas among a lot of other things.