Coax Questions

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ra7850

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In my scenario, my antennas are located in the attic. Unfortunately I have an HOA. The highest peak of the roof to where my radios are also located in the attic is less then 50 feet. The roof doesn't appear to be an issue, meaning it doesn't appear that there isn't any metal under the shingles. It's not the bests scenario, but without a lot of grief it's what I have to deal with. My idea was to use LMR400 to a panel using bulkhead connectors then run the last 3 feet to the scanners. I usually listen to the local stuff in the 154.000 to 159.995 range, I can occasionally hear milair traffic, and the local airports. There are a few trunk systems in the area and the county is migrating to a new radio system that has yet been determined. I have the LMR400 left over from my previous residence, I'd still need to purchase connectors. I thought about using LRM240 but would require both the new cable and connectors, or buy the 50 feet of cable with the connectors preinstalled. My location is in Luzerne County, PA. The antenna I'm using is a scantenna/St2 from the old Grove Enterprises. Since I have the HOA, I'd like to use the best cable setup possible within reason.

Thanks,
Robert
 

mmckenna

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LMR-400 is decent cable, and if you can install your own connectors, that's what I'd go with.

Using a jumper of something more flexible is a good idea for making the final connection to your radio.
 

Ubbe

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A RG6 coax at 900MHz and 100ft attenuates 6dB and a RG11 5.2dB and that's just a 0,8dB differerence. At 50ft it's a 0,4dB difference and less than that at lower frequencies like 155MHz it's half of that.

RG11 are twice as thick and hard to bend and need special connectors and it seems to be used for outdoor and burial puposes and costs twice as much as RG6.

/Ubbe
 

ra7850

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A RG6 coax at 900MHz and 100ft attenuates 6dB and a RG11 5.2dB and that's just a 0,8dB differerence. At 50ft it's a 0,4dB difference and less than that at lower frequencies like 155MHz it's half of that.

RG11 are twice as thick and hard to bend and need special connectors and it seems to be used for outdoor and burial puposes and costs twice as much as RG6.

/Ubbe
The ST2 is presently using RG6.

Thanks Ubbe
 

prcguy

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I think you looked at the wrong chart, RG-11 is closer to half the loss of RG-6 at any frequency but you must compare the same low loss foam dielectric types of cables like CATV or Satellite. There is an RG-11 version with the older solid hard dielectric and copper braid which is much more lossy than CATV or Satellite types and that shows up on Internet loss calculators a lot. All the charts I see for low loss types put RG-6 near 6.5dB loss for 100ft at 1GHz and RG-11 at 3.9dB loss for the same. That is worth upgrading to RG-11 on an long run.

Connectors for RG-11 are not special or not any more special than RG-6, there is a lot of compression types identical to RG-6 but bigger. I've run literally miles of RG-11 and I have 1,000s of ft of it around here and bags of T&B Snap-N-Seal connectors. The Belden RG-11 here is soft and pliable and bends almost as easy as RG-6. Should I just make up a run and send to the OP?


A RG6 coax at 900MHz and 100ft attenuates 6dB and a RG11 5.2dB and that's just a 0,8dB differerence. At 50ft it's a 0,4dB difference and less than that at lower frequencies like 155MHz it's half of that.

RG11 are twice as thick and hard to bend and need special connectors and it seems to be used for outdoor and burial puposes and costs twice as much as RG6.

/Ubbe
 

Ubbe

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OP only needed 50ft so at 800MHz and lower it's less than 1 dB in difference according to your chart. So generally speaking RG11 isn't worth it, if you don't gonna burry it under ground and already have the tools to fit those connectors, or gets the coax with connectors fitted for free.

/Ubbe
 

ra7850

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On a side note about positioning the St2 antenna, I currently have it mounted as high as it can go to the peak of the roof centered between to trusses, pics are below. my question is, could the trusses be causing signal degradation? I could build something to mount it from that would be on the floor of the attic.with no obstructions just open space. The drawback is it wouldn't be as high as it is now.

Thanks,
Robert
 

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WB9YBM

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Do I understand correctly you're planning to use three feet of connectors? EEEEEEEEEEEEEEEEEEEEEEEEEEEEEK!!!!!!!!o_O
 

WB9YBM

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No, the plan was to run the cable from the antenna to a patch panel of sorts, than use a short cable to scanner.
that makes more sense. In fact it's similar to what I used at the communications R&D lab in Motorola. One suggestion: you might want to think about grounding the box. Even if you're already grounding at the antennas outside, it's a good back-up if you get a serious thunderstorm. Just a thought.
 

ra7850

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OK so now that the cable post has been narrowed down, does anyone have any thoughts on the second part of the post? See post #10 for the pictures.

Thanks,
Robert

On a side note about positioning the St2 antenna, I currently have it mounted as high as it can go to the peak of the roof centered between to trusses, pics are below. my question is, could the trusses be causing signal degradation? I could build something to mount it from that would be on the floor of the attic.with no obstructions just open space. The drawback is it wouldn't be as high as it is now.
 

Ubbe

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It's usually a high impedance at the tip of antenna elements and are then prone to be interfered by anything that can contain moist or particles that are RF sensitive. Best test are to stand in the attic with the antenna connected to a portable receiver and then monitor a weak signal in the band of your most interest, in analog mode on the receiver, and just test what the antenna receives when you move it around and gets close to different structures in the attic.

/Ubbe
 

ra7850

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It's usually a high impedance at the tip of antenna elements and are then prone to be interfered by anything that can contain moist or particles that are RF sensitive. Best test are to stand in the attic with the antenna connected to a portable receiver and then monitor a weak signal in the band of your most interest, in analog mode on the receiver, and just test what the antenna receives when you move it around and gets close to different structures in the attic.

/Ubbe
Thanks /Ubbe, I'll try that today.
 

IQ_imbalance

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I think i remember seeing somewhere that someone concealed a short ?VHF/UHF? vertical in a piece of PVC and stuck it on their roof as a "sewer vent".
If you're interested in HF at all look at the loop-on-ground....
 
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