need advise
- Thread starter HOLEBILLY
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For a 75ft run at 800 Mhz...
Lmr 400 should be the minimum.
You really need to be running hardline at that length.
You can get remnants off of ebay occasionally.
Anything less than LMR, and you will lose the gain you get by using a yagi.
Conversely, you could run RG-6U to a mast-mounted pre-amp, and then do
the run of RG6U Quad Shield.
6 of one..
Lmr 400 should be the minimum.
You really need to be running hardline at that length.
You can get remnants off of ebay occasionally.
Anything less than LMR, and you will lose the gain you get by using a yagi.
Conversely, you could run RG-6U to a mast-mounted pre-amp, and then do
the run of RG6U Quad Shield.
6 of one..
mast mount amp
what would be an ok mast mount amp. I have only seen them over $150. Where can I get one.
what would be an ok mast mount amp. I have only seen them over $150. Where can I get one.
trainman111
Member
Where I ordered my LMR-400 from was www.therfc.com. I think the coax was .79 a foot. They were very helpful and explained everything about assembling the connectors for me. I would definately recommend them.
jonny290
Member
This is only partially correct.
You "lose gain" by losing signal in the coax, but at 75 feet, you're going to pick up signals that you won't even hear at 30 feet, and they'll be more than powerful enough to bust through the 6db of loss you have or whatever. Your radio horizon is much larger at 75 feet elevation. Otherwise we'd all just be soldering quarter wave whips to the antenna terminals of our radios.
In addition, advising "LMR400 at the least, more likely hardline" is kind of scary to casual users. I see it a lot, and it's not really accurate. You know as well as I do that about 2% of scanner listeners are of a caliber at which they require hardline, and if they do, they're not posting on radioreference asking what type of coax to feed their antenna.
OP, you will be satisfied with this setup by running any .405" coaxial cable; RG-8 at the minimum, and LMR400 and Belden 9913 is better.
wildbillx said:
I use an 18db gain single port Electroline commercial cable drop amp. Ebay for ~ $20
RG-6 Quad Shield provides the power up to it. It sits in a weatherproof Hoffman box
on the mast, just below the yagi.
Short jumper from antenna to amp in box.
Two longer cables to the shack. One to provide power up to the box, the other for signal down to the Spectra.
It's a good setup for me to receive a system that's particularly difficult to hear because
of distance and downtilt.
My next project will be using some hardline remnants for a couple of 800 systems.
zguy1243
Member
75 feet of Rg8 at 800Mhz frequencies will be a disaster, unless the stuff hes trying to listen is fairly strong. Is the antenna at 75 feet above the ground or do you just need a 75 foot run to get the coax where you need it? I would Run LMR600. There is a company on ebay now selling it for .89 cents a foot new. Then run some kind of a preamp down by the radio. The LMR600 will be a life saver compared to RG8 at 800mhz at those kind of runs.
zguy1243 said:
Hardly a disaster...
At 850 MHz, LMR400 shows a loss of 2.8 db for 75', and RG8 is 5 db for 75'. So, the difference in loss between RG8 and LMR400 in that installation would be around 2.2 db - certainly not optimal, but I'd hardly call it a disaster. Get the best you can afford, and is available to you. RG6, btw, is 6.7 db for 75', a difference of almot 4 db.
Let's put something into a better perspective... 2 db sounds like a lot, and when you're losing watts in a transmitter line, it can amount to a lot of power. But let's look at the typical scanner receiver with .25 microvolt sensitivity. That 2 db is the difference between .25 and .31 microvolts. You could measure the difference, but in practice, you'd probably barely notice it if you were trying.
zz0468 said:
Commscope RG6 Quad Shield is 5.5db per 100 ft. About the same as 75ft of RG-8.
5.5 DB loss is almost twice the loss of the signal reaching the receiver (3db is half). More than made up for with the mast-top cable drop amp.
At 800Mhz the coax is CRITICAL.
Get the best you can afford is really the correct answer.
That Commscope loss specification is meaningless without referencing a frequency. Is that 5.5 db/100' at 850 mhz? Is so, that's pretty decent. But if that's the 150 MHz loss, better check the chart again. It makes a BIG difference. Coax cable loss must specify frequency and length, or it doesn't mean a thing.
I also wouldn't use a cable tv amp. If it's not designed for weak signal, low noise operation, it may appear to make signals stronger, but it could also be adding more noise than signal, and actually reducing the receiver's ability to detect a weak signal.
edit: that spec IS for the 800 mhz range.
I also wouldn't use a cable tv amp. If it's not designed for weak signal, low noise operation, it may appear to make signals stronger, but it could also be adding more noise than signal, and actually reducing the receiver's ability to detect a weak signal.
edit: that spec IS for the 800 mhz range.
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zguy1243
Member
I have a 4 port Scientific Atlanta CATV drop amp, Its puts each of the 4 outputs up +7db. I Also have a high dollar low noise preamp from Anglelinear that has a noise figure of less than 1 db compared the 3.5 or less NF of the Scientific Atlanta model. Also the Angle linear amp pushes 20 Db across the milair band and about 12 db on up to 900 megs or so. The difference between the two are so small that it takes a very large s-meter and good ear to tell it. I gotta say that the scientific atlanta models are a good built amp.
zz0468 said:
I don't doubt for a minute that the SA is a good amp. But it's a distribution amp, not a preamp. That could very well be making your s meter read higher, and reducing your ability to hear weak signals at the same time. The Angle Linear amp is in a league of it's own.
zz0468 said:
870Mhz on the Commscope.
And the drop amp works fine close to the antenna, even with the crappy 2db noise
signature.
Of course YMMV if you live next to a Nextel tower.
zz0468 said:
Well it was a disaster for me. I switched from RG8 to RG11 (around 60ft) and since then I am picking up 800mhz systems that I never even came close to picking up with the RG8 (even with an amp).
Yep, me too. I went from it to Andrew harline with a RadioShack small barrell preamp at the antenna. The difference was night and day.
zguy1243
Member
Yeah RG11 is great stuff man, For the money you cant beat it. For runs up to 75 feet i would not hesitate to use RG11, I love it.
Dubbin said:
zguy1243 said:
You can use it for a heck of a lot more then 75'. Oh and I got a few hundred feet of it still on the roll for free
A buddy of mine worked for a cable company, he said they throw away anything under 300'.Dubbin said:
That's quite a dramatic change for cables that only have 1.1 db difference in loss (for 60 feet). I'd seriously suspect that some other factors are involved besides just specified cable loss. Perhaps the RG8 run was just plain bad, or a connector was improperly installed. Fact is, the cable specs show RG11 is 2 db better per 100' at 800 MHz than RG8 is. That 2 db would quiet a slightly noisy signal just a bit. But it's simply not enough to account for bringing something from being completely unreadable to usable. Remember, a 1 db change is barely detectable by the human ear if you're looking for it. 2 db isn't much more detectable than that. 3 db is easily discerned, but it is not a dramatic change, especially for quieting fm signals. A 3 db improvement would bring something from the threshold of being detectable, to an annoyingly noisy signal that you don't want to stop to listen to.
Now... having said all that, if you chase after a db or two in your coax, select an antenna that has a couple of db gain in the directions you need it, and don't throw it all away by running it through a noisy distribution amp for the sake of higher s meter readings, all those minor improvements will actually add up to something that you can really notice.
reference: Belden 8237 RG8 vs Belden 8213 RG11.
http://www.ocarc.ca/coax.htm
zz0468 said:
Nope nothing was wrong with the coax or any of the connections. At first I was thinking that same thing so I replaced it all but it made no difference. BTW it was RG8X that I replaced with the solid center RG11. I think you will find a bigger difference between the two.
Dubbin said:
RG8X!!?? I sure wish you had said so in the first place. You would have saved me some wear and tear on my keyboard! RG8 and RG8X are so NOT the same thing.
RG8 (Belden 8237) : 3.8 db loss for 60' at 800 mhz.
RG11 (Belden 8213): 2.7 db loss for 60' at 800 mhz.
RG8X (Belden 9258): 7.3 db loss for 60' at 800 mhz.
That's about a 4.5 db difference, not the 1.1 db difference as with regular RG8. Now, that's getting pretty noticeable. I KNEW there was more to the story! =)
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