Question about antenna placement and nearby trees...

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sffiremedic

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I put up an 800mhz base antenna. I am trying to pull in an 800mhz trunked system across the bay with a small hill 50 yards to my west, so I am getting a signal which I would like to improve without going up higher with the antenna.

The antenna is at the rear of my house. Directly in line of sight, in my front yard is a pine tree, about 60' from the antenna and taller than the antenna. My question is how does this tree affect the signal coming over just over the small hill? If I move the antenna to an adjacent side of the house so the tree is not "blocking" line of sight (which the small hill blocks to some degree) will my signal appreciably improve?
 

mmckenna

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I run a trunked 800MHz system, and while heavy foliage can impact coverage, it's likely not an issue for you. But, you could try moving it and see if it improves a bit.

Likely the small hill between you and the bay is part of the issue. This is "topographical" shielding, or just plain "too much dirt in the way"
But there is obviously a signal there to work with, which is good. Improving antenna gain and/or reducing feed line losses will help your radio.

So, what kind of antenna are you using?
What kind of coaxial cable and how long is it?
 

sffiremedic

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I picked up a Laird 800mhz base station antenna off C-list, actually two of them, $25 each, they are about 5’ tall. The cable is RG6 Quad that Comcast left me, new off the spool, think close to 100’ of which I can lop off about 30’ when I pick up some F connectors. The Laird has 6dbd gain and oddly enough across the bay the 800mhz signal is not any better than with the discone I took down, which led me to think about the tree.

I realize I should get LMR400 cable for the Laird. The RG6 was fine for vhf hi and low with the discone. I plan on moving the Laird to a different roof peak to avoid the tree. Will run two scanners off the discone (Pro-2006, 780xlt) and two off the Laird 800 (Pro-668 and an sdr/laptop).

One note on this Laird, the pig tail goes up into a deep well to the antenna connection, but the pigtail only tightens so far and then
spins with some resistance. Made me wonder what the connection was like on the other side, inside the fiberglass rod cover, which does not appear removable. But I am getting signals so....I would like to try the second Laird, no pigtail, not sure what tool would reach up into the well to properly to tight the coax.
 
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Ubbe

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Do you have a model number or a picture of that 800MHz antenna? Base station antennas often means cellular antenna and could be narrow banded and do not cover the frequencies you are trying to receive. It could also have been design as downtiltet that sends the radio waves downwards to get a smaller cellular coverage.

/Ubbe
 

sffiremedic

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Do you have a model number or a picture of that 800MHz antenna? Base station antennas often means cellular antenna and could be narrow banded and do not cover the frequencies you are trying to receive. It could also have been design as downtiltet that sends the radio waves downwards to get a smaller cellular coverage.

/Ubbe
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Ubbe

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A vertical omni at 8dBi, presumably at 850MHz, are much better than a discone and should receive better with the signal level you have to deal with. The bandwidth are around 10% which seems to be the normal standards for antennas.

Maybe all signals you get are coming over the top of a hill and you can't have a high gain antenna if the directional loob are extremly flat like a pancake and it goes straight into the hill and not over it. Can be tested by tilting the antenna backwards. Best are to directly connect an antenna to a portable scanner and then move antennas around in different spots and tilt them in different directions to try and find the best location for it.

I relocated my airband antenna from the chimney to a little hill in the backyard that are lower in hight. But next to a little pine tree I had much better reception and where thinking of hanging it from a branch, but then I had an equally good signal at that same hill but on top of my sat dish that are mounted to a metal pole. That was a more suited place for it and I used two of those $10 combiners that have one input for 700-2500MHz and another input for 25-700MHz and I could then use the existing sat dish coax. I measured the combiners and it was less than a 0,5dB loss and 100ft of RG6 that I use for the dish hardly attenuates anything at VHF.

/Ubbe.
 

Kaleier1

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I picked up a Laird 800mhz base station antenna off C-list, actually two of them, $25 each, they are about 5’ tall.
I have a nearby 900 Mhz system about 3 miles away from me. Couldn't pick it up at all with an indoor scanner or SDR dipole telescoping antenna. Thought the RR database was wrong on the frequencies because I could pick up another system next to it without a problem.

So I bought a 9 element 13 dBi 806-960 MHz yagi antenna here for $15.31 and free shipping. They estimated 4 weeks for delivery but I got it in 10 or 12 days. It comes with an F style connector (most comes with N type) and mounting U-bolts. I put the antenna indoors and could receive most of the frequencies but the control channel was too weak to be reliable. I then put the antenna up on the roof on my TV antenna mast pointed toward the system and it comes in solid, control channel and all. I even put a splitter inline to use the antenna with an SDR dongle which reduces the signal by 3 dB but still have a strong solid signal.
 

sffiremedic

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Damn that the epitome of Chinese"quality" :). But hey if it works, the price is right...and if it ever dies, you know the concept is proven.

I have a Larsen 12dB yogi but it is 898-960mhz. I wonder how it will work at 760mhz? Anyway I am going to climb on the roof and see.
 

WB9YBM

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non-metallic items like trees, especially at higher frequencies, can be considered "radio opaque"--yes, they'll attenuate the signal but not as bad as metal items. I've noticed this first-hand, at least to a limited extent, at 220MHz (ham band) when trees have leaves in the summer versus no leaves in the winter, particularly at the extreme range / weak signal work...
 

sffiremedic

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I have noticed at my Mom's house back east, the TV reception is great in fall after the leaves come down. Line of sight to the towers needed.
 

sffiremedic

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So I got up on the roof with my Pro-668 and the Larsen Yagi 12dB 898-960mhz , point towards the NW trunked simulcast system I had not been getting with the Laird omni 6dB mast. Immediately I pulled in talk groups from the 760mhz simulcast I had been missing! Hopefully I will still get it with a 70' run of quad RG6, but I can get LMR400 if needed, I do want to combine with the Laird mast and then split inside for two scanners, and the two conventional scanners sharing the discone I put back up on the original pole. The Laird and Larsen with be on another peak over 30' away and the Laird/Larsen will not be blocked by the pine tree.


I have a nearby 900 Mhz system about 3 miles away from me. Couldn't pick it up at all with an indoor scanner or SDR dipole telescoping antenna. Thought the RR database was wrong on the frequencies because I could pick up another system next to it without a problem.

So I bought a 9 element 13 dBi 806-960 MHz yagi antenna here for $15.31 and free shipping. They estimated 4 weeks for delivery but I got it in 10 or 12 days. It comes with an F style connector (most comes with N type) and mounting U-bolts. I put the antenna indoors and could receive most of the frequencies but the control channel was too weak to be reliable. I then put the antenna up on the roof on my TV antenna mast pointed toward the system and it comes in solid, control channel and all. I even put a splitter inline to use the antenna with an SDR dongle which reduces the signal by 3 dB but still have a strong solid signal.
 

WB9YBM

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I have noticed at my Mom's house back east, the TV reception is great in fall after the leaves come down. Line of sight to the towers needed.
That reminds me of a few folks I heard about back in the analog TV days that put up a tower for TV reception--they lived half way between Milwaukee, Wisc. & Chicago, IL and would either turn their TV beam to whatever city they wanted to see and--because of the height of the tower--do TV DXing across Lake Michigan...
 

gnuuser

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you are using rg6 which is a 75 ohm impedance cable ( this would be fine if you co-phased two antennas) but with just a single antenna you want at least rg8x low loss cable.
800 mhz signal travels faster than lower frequencies but can be easily attenuated by the surrounding topology. (primarily if the earth is iron rich as it will absorb radio waves) and quite often dense vegetation can reflect it away.
depending on the atmospheric conditions you can bounce a signal but remember with each bounce it will get weaker.
 

krokus

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So I got up on the roof with my Pro-668 and the Larsen Yagi 12dB 898-960mhz , point towards the NW trunked simulcast system I had not been getting with the Laird omni 6dB mast. Immediately I pulled in talk groups from the 760mhz simulcast I had been missing! Hopefully I will still get it with a 70' run of quad RG6, but I can get LMR400 if needed, I do want to combine with the Laird mast and then split inside for two scanners, and the two conventional scanners sharing the discone I put back up on the original pole. The Laird and Larsen with be on another peak over 30' away and the Laird/Larsen will not be blocked by the pine tree.
I would rethink the combining of the Yagi with other antennas. Run the Yagi to the scanner for the distant system, then maybe combine the others, and use a good distribution setup. (Not a splitter.)
 

gmclam

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I am wondering if there is only one tower you can pick this signal up from. Sometimes you get better reception from a tower further away.

When comes right down to it, the issue is getting as much signal strenth at your radio's antenna input as reasonably possible. Look at the spec for the cable you're using at the desired frequency and cable length. Keep the cable as short as reasonably possible. A tree in the way will attenuate the signal, which could put it over the edge of being able to receive it.

A directional antenna will give you "free gain" of the signal. It could mean having a dedicated antenna for this one system. Also note some scanner models have better receiver sensitivity than others. If you don't have a problem with interfering signals, more sensitivity will help.

I see you want to split the signal between multiple radios. The best way to do that is with a multi-coupler. They amplify the signal to make up for the loss of splitting. But they amplify everything. I have a dual filter at the input of my multi-coupler to remove AM & FM broadcast signals (they are stronger than you think). You might consider a band-pass filter that only lets through what you're trying to monitor.

To answer your original question, you are probably better to point the antenna directly at the tower, even if a tree is in the way. I'd rather receive through a tree than a hill. Raising the antenna, if if removes the tree from being in the way is good; but that means you'll need longer coax. The loss of signal through more coax may be greater than the improvement of raising or moving the antenna.
 
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sffiremedic

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I am only considering combining the 800 Yagi with the 800 omnidirectional mast. Why is this a bad thing?

The discone is on another part of the roof 35' away.


I would rethink the combining of the Yagi with other antennas. Run the Yagi to the scanner for the distant system, then maybe combine the others, and use a good distribution setup. (Not a splitter.)
 

sffiremedic

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you are using rg6 which is a 75 ohm impedance cable ( this would be fine if you co-phased two antennas) but with just a single antenna you want at least rg8x low loss cable.
800 mhz signal travels faster than lower frequencies but can be easily attenuated by the surrounding topology. (primarily if the earth is iron rich as it will absorb radio waves) and quite often dense vegetation can reflect it away.
depending on the atmospheric conditions you can bounce a signal but remember with each bounce it will get weaker.
I feel we are beating a dead horse with the 75 ohm RG6 debate. People say it does not matter on receive only, others say it does but is negligible under 100'. I have used 9913 once and needed it for that application, but Bill Cheek used to recommend RG6 for most applications.
Also all RG6 is not created equal although all are 75 ohm. Basically if it works, it works. If I have to upgrade cable I will, but may not need to.
I will update.

This IS a budget setup. Simpler/cheaper is better if it meets its goals.
 

jim202

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One thing you haven't mentioned is what type of pine tree your dealing with. Down here in the south we have mostly the long needle pine trees. The issue with them is that the length of the needles is close to the wave length at the 700 trunking frequencies. As such they are a real pain and absorb a good amount of the signal. They also cause problems with the cellular signal. So around here you will find the towers for these signal spaced much closer than in other parts of the country.
 
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