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What is traditionally best coax for 800mhz scanning

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peq387ab

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#1
I have been using R6 for scanning 800mhz, roughly about 50 feet of coax line. Since I'm gonna be taking down my antenna before winter hits and move it to a different location, I thought I would ask the fellow RRs what are thoughts for coax if RG6 is the best quality for loss and such. I'm gonna be having a 50-75 foot run of cable and the antennas will be off the ground about 30 feet.
 

lou9155

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#4
lmr 400 changed my 800 mhz reception .. i have a 75 foot run ,using rg8x i couldnt get a tower 10 miles away..switching to lmr 400 i get 5 solid bars. research attenuation losses for various coax types you need low loss for 800 mhz
 

NC1

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#5
I will be moving in the near future and am planning something similar to what you are considering. In my research, I have come to the conclusion that I really do need a high quality cable and the money will be well spent in the long run.

The only coax cable I am considering are:

#1) Andrew Heliax LDF6-50A
#2) Times Microwave TMS LMR-900
#3) Times Microwave TMS LMR-600
#4) Belden 9913

The reasons are obvious once you run all your details through the below linked Coax Calculator.
Once I saw the huge losses at the higher frequencies, I know I will be very unhappy if I compromise the quality because of cost. I have used the lower cost cable most of my life, and recently came upon a new 50' length of Belden 9913 for a few pennies on the dollar - and all I can say is that I will never, never, never, go back to using crappy common cable again. It is a massive difference!

Take a look for yourself and run your scenarios through the calculator:
Coax Calculator
 

peq387ab

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#6
Thanks for the info guys. I have looked into LMR 400. Might have to invest in it. My RG6 does do well, but with 75 feet of run, there is some loss in it. Live in flat area, usually can get sites about 25 miles away on any given day, but during ducting days it's better. I do notice some fringe sites are trying to always come at about 30-40 miles away
 
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#7
"Best" as a qualifier, means a lot of different things to a lot of different people.

It really depends on your budget, however there is a diminishing level of returns, and at some point it just gets silly.

If what you have is working well enough, then stick with it. But, since it looks like you are adding 25 more feet to your run, upgrading -may- be necessary to keep the coverage the same.

LMR-400 is a good step, but it's not the "best" coax by a long shot. It is reasonably priced, easy to find and flexible enough to install easily in most residential applications.

Depending on the exact brand/grade RG-6 you have, you could be losing around 65% of your received signal in your current application. Using the same RG-6, your losses get close to 80% at 75 feet. That might not be an issue if you have a good antenna and a strong signal to work with.

LMR-400 will improve things. At 75 feet, you'll lose almost 50% of your received signal to feed line losses. That's a bit better than what you might be seeing now with good RG-6, but not a huge amount. It's a bigger improvement than if you went with 75 feet of RG-6.

You can quickly escalate things chasing signal losses: LMR-600, LMR-900, 1/2" heliax, 7/8" heliax, 1-5/8" heliax…. it all gets expensive and the connectors get expensive. At some point you need to decide when it's "good enough". Best will always be a fleeting target.
 
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#8
When dealing with 800MHz signal and trying to receive weak stations, it's always best to use quad shield RG6 cable, which is very cost effective, and add an amplifier if the lenght is too long. An amplifier with low internal noise like 0.6dB NF will most likely also improve the scanners performance as the first amplifier in the scanner usually have a 2dB NF level at its best. Thats a 1.4dB increase in reception right there that the best coax in the world can't beat. All coax attenuate and cannot increase a signal by 1.5dB

/Ubbe
 
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#9
When dealing with 800MHz signal and trying to receive weak stations, it's always best to use quad shield RG6 cable
No. An amplifier introduces additional noise into the system, and may introduce intermod and other interference as well. If you can solve the problem with lower-loss coax, it is better to do so than to add an amplifier. You'll have less noise and distortion.
 

peq387ab

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#10
Thanks guys. As far what I will do for my fall project from a little more research is use LMR 400. I think there will be some noticeable loss gain from RG6. As far as RG6 I have just always used standard RG6 similar to what you would purchase at a Walmart or Radio Shack for cable TV. I monitor the Minnesota ARMER 800 MHz system. I think there will be a gain of a few sites that try to come in on the fringe as well. I guess I have just always used RG6 and it has been okay for 800
 
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#11
RG-6 can work pretty well. Problem is that there are a lot of variations as to quality of cable. Retail outlets like Wal*Mart and -especially- Radio Shack often have very low grade stuff. Getting the high quality stuff like the cable TV companies use would probably be an improvement over the Radio Shack stuff.

However, LMR-400 is a good option. It's a manageable cable, as in it is flexible enough to route inside walls, if you want to run it that way. The larger cables get a bit difficult to route.

Waterproofing your outdoor connections should be a top priority. Water will get inside the connectors and make a mess. Spending some time doing a proper waterproofing job should be a no-brainer.

Also, LMR-400 is quite a bit stiffer than the RG-6. I'd strongly encourage you to -not- try to connect it directly to your radio. It's a sure way to damage the connector on your expensive scanner. The weight of the cable, and connector make it kind of ungainly. It's industry practice to run a short jumper of a smaller, more flexible cable between the end of the heavier coax and the radio. RG-58 would be fine in a short length.

If you don't have a lot of experience terminating coaxial cable, you can purchase pre-made cables that can make life easier. Get connectors installed that match your antenna, so you don't have to use adapters. On the radio end, terminate with a female N connector or female BNC connector. Those are low loss connectors. Get the short jumper to the radio made to connect to the female N or BNC connector, and the other end to match your radio. While some will try to tell you to make your own cables, unless you have the right tools and some experience, it can be a frustrating experience. Since good connectors can be expensive, you probably don't want to waste a bunch on practice. Nothing wrong with ordering pre-made cables...
 

iMONITOR

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#12
I have been using R6 for scanning 800mhz, roughly about 50 feet of coax line. Since I'm gonna be taking down my antenna before winter hits and move it to a different location, I thought I would ask the fellow RRs what are thoughts for coax if RG6 is the best quality for loss and such. I'm gonna be having a 50-75 foot run of cable and the antennas will be off the ground about 30 feet.
What antenna will you be using? Any obstructions between you and the signal source?
 
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#13
The only coax cable I am considering are:

#1) Andrew Heliax LDF6-50A
#2) Times Microwave TMS LMR-900
#3) Times Microwave TMS LMR-600
#4) Belden 9913http://www.qsl.net/co8tw/Coax_Calculator.htm
Really?

One of these things is not like the other, and probably doesn't belong on that list.

LDF6 is obsolete, and it's got a 1 1/4" diameter solid copper outer conductor. The stuff is like wrestling an Anaconda to install, and it's what you see on cell sites with tall towers. The connectors alone are probably $100 each.

LMR900 isn't much better. It's usually used as a jumper for a 2 1/2" line.

LMR600 is over 1/2" thick.

How long a run are you contemplating? If you consider the actual length required, and calculate the loss for a more reasonable coax, you can convert to something that might be more understandable, like microvolts. For a digital or FM system like you'll find on 800 MHz, a typical scanner threshold might be -113 dBm, or about 0.5 microvolts. Three dB less is -116 dBm, or about 0.35 microvolts.

It might take playing with a signal generator to see it, but the difference between -113 and -116 is barely perceptible. You'll only notice the difference on really weak signals that are almost unusable anyway, so you might want to do a better cost-benefit analysis of that LDF6.
 
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#14
My 2 cents (take it for what it's worth). You can nearly always spend more money (often lots more money) for better coax, but will you really get better results? Also folks will always say that this coax works great for them and that that coax is nothing but crap (also for them) but you still don't know how it will work for you (which is what's important for your listening anyway).

You can spend a few cents per foot and not much more for connectors and get a great signal (take RG-6 Quad for example) or spend several hundred (if not thousands) per foot for some ultra low loss rigid coax and hundreds more for connectors (both must be professionally installed and your tower very strong to support the very heavy weight - a 90 degree elbow can be nearly 50 lbs on its own) and still not get a good signal (both depending on your specific situation).

Many types of coax are sold using just generic labeling (RG-8 for example) and from one manufacturer it may be quite good but from another rather bad (but both look identical to the typical user). Also watch out for similar sounding types that have drastically different specifications (RG-8 and RG-8X for example). Also some coax may use different numbers for the same base type (Belden 8214, 8237, and 9913 are all RG-8 class coax) but have different specs. I say this not to scare you off, but to let you know that you really need to check exactly what you'll be getting prior to you sending off your order. Start with a good coax loss calculator (several are online, just search) that not only states the type, but also brand and model number for the generic coax types.

Does the coax loss really matter? Well, yes but perhaps not as much as folks may believe. You may hear "3 dB is half your signal!!!", OK, that may be true but it's not the full story. Think of it this way, your drive from home to work may burn a gallon of gas and your tank holds 13 gallons. Must you really have a full tank every day to make it safely to and from work? Chances are you can fill up only once a week and be fine (depending on how much other driving you do that week). Your radio needs a certain amount of signal to pick up anything at all. As that signal increases, you'll get better and better reception until you reach a certain level where you have a clear, noise free signal. As you add more signal you will notice no difference until you reach a level where you saturate your radio's front end and your reception will get worse and worse as your signal increases (yes, too much signal is an actual problem!!!).So long as you stay in the sweet spot where you have a clear, noise free signal you're good.

Also know what frequency range (or ranges) you actually use. It makes no difference if your radio will pick up a very wide range if you only listen over a very narrow range. Optimize your antenna system (antenna, coax, amps - if any, filters - if any) to work on the range you use. It's like having a TV with hundreds of channels but you only watch ESPN. So long as ESPN works, who cares if the signal for your local school board meeting comes in clear.
 
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#15
Does the coax loss really matter? Well, yes but perhaps not as much as folks may believe. You may hear "3 dB is half your signal!!!", OK, that may be true but it's not the full story..
As you state above, "3 dB is half your signal!!!". True, it's half the power, but a receiver isn't really a 'power sensitive' device, it's a 'voltage sensitive' device. That translates to the fact that half the power delivered to the receiver is not really "half the signal".

Where a 3 dB difference in power is twice or half the power, a 6 dB difference is twice or half the voltage, and in a receiver, it's the voltage delivered to the receiver that you're chasing. You'll note that transmitter power is usually measured in watts, and receiver sensitivity is usually measured in microvolts.

You can convert it all to dBm and just add and subtract the gains and losses, but in the end, where 3 dB loss is only 50% of power, it's 70% of the voltage, and that's not "half the signal". It's 3/4 of the signal.

In a receive system that's used for listening to public safety and other LMR type stuff, it doesn't make sense to spend wads of money to chase a couple of dB. Other modes, like CW or SSB, that couple of dB can make the difference between detecting a signal or not, but with a scanner, you'll never notice it. Start talking 6 dB or so, and the differences become perceptible, but only at weak signal levels.

This is where a cost-benefit analysis must be done. In a real public safety system, engineers will chase every last dB down... that 3 dB might make the difference between a call for help being barely understood in the static, or just barely unintelligible. Where lives matter, the expense of the cable becomes worth it. $1500 for a run of coax that will last 20 years and give every last ounce of performance is well worth it. But in a home installation? You'd be wasting your money.
 

JamesO

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#17
Forget the over priced coax. Do not listen to anyone that complains a good LNA just adds noise and will intermod, they have NO first hand experience in picking a quality LNA and setting it up properly. In very few harsh RF environments you could have problems with a LNA, but it is not likely in most configuration.

Suggest you read this thread: https://forums.radioreference.com/s...mp-10-off-december-other-useful-rx-items.html

There are very few people here that understand how a properly set up LNA works and the benefits of such, Ubbe and rbm are the few members here that actually understand and "get it".

You WILL NOT be disappointed with a properly set up LNA as outlined in the thread linked above. If you listen to the negative comments, you WILL be missing out with everyone else.
 
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#18
Forget the over priced coax. Do not listen to anyone that complains a good LNA just adds noise and will intermod, they have NO first hand experience in picking a quality LNA and setting it up properly. In very few harsh RF environments you could have problems with a LNA, but it is not likely in most configuration.

Suggest you read this thread: https://forums.radioreference.com/s...mp-10-off-december-other-useful-rx-items.html

There are very few people here that understand how a properly set up LNA works and the benefits of such, Ubbe and rbm are the few members here that actually understand and "get it".

You WILL NOT be disappointed with a properly set up LNA as outlined in the thread linked above. If you listen to the negative comments, you WILL be missing out with everyone else.
This post is so wrong on so many levels.

1. It's impossible for YOU to determine what's a "harsh RF environment" that may exist at anyone else's installation by remote control over an internet forum. Left to it's own devices, the preamp will be the final judge of that.

2. I have about 40 years of professional experience in RF from DC to daylight, and I have personal experience watching the best quality preamps go into overload when conditions allow.

3. Without proper filtering, preamp overload is not only possible, it's likely.

4. I have seen your pissing match with prcguy in the other thread. Truth be told, I'd back his technical comments over just about anyone else on here. The guy is pretty damned sharp.

A good preamp is a joy, but they don't always make things better, and they're not always well behaved without help. I'm glad your preamps work so well for you. That's all special and stuff. But quit telling everyone that they are an instant panacea for everyone everywhere. As soon as you go down that road even a little bit, you'll be wrong.
 

JamesO

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#19
Well I have plenty of real world experience and have used a number of LNA's at many locations and have had good luck with almost every configuration. Again, some common sense and picking the proper product is part of the equation. Some cases could be problematic for a wideband LNA, these are often the exception.

I would say I am located in a very harsh environment being just a few miles from Washington, DC with not only MANY Public Safety systems but probably more Federal Government systems then you will find almost anywhere else in the US.

I have multiple cell towers between 1-3 miles from my antenna and the majority of the DC market TV and FM broadcast towers are within 4-7 miles of my location. I have a flight path that often puts commercial airline traffic directly over my house, but the normal flight path is as close as 1 mile from my house.

I would say few of the members here are in a worse environment than I am, but some are and they may have some challenges with trying to use a LNA. But as I stated above, there is also some planning that goes into what LNA is chosen and why. There are plenty of Pre-Amps, not all are created equally.

Like anything, until you try a set up, you may not know how well it will perform, in some cases you will have some challenges, but most challenges can be addressed as needed. Although far from ideal, the LNA can even be put mid coax path or right at the receiver, however, if the LNA is put right at the receiver, the radios attenuator or an input attenuator may be required.

While you may have 40 years of experience, also understand what you may have worked with even 10-20 years ago is not likely as robust and of a low noise as some of the more reasonable options are available today.

What I am trying to do is OPEN up some people minds here, not to listen to all the negativity and consider using a quality LNA and they will find for themselves they are missing a lot of signals in their area. In only a small number of cases, I would expect problems and often it takes some trail and error playing around until things are optimized. I had a severe FM Broadcast problem I had to address and probably tried half a dozen FM Broadcast filters until I found one that worked very well.

I am offering solutions that I spent a fair amount of my time and money fine tuning and I am sharing what I have with other members of the community.

So you can live with what you have, but until you try what I have suggested, you are the one missing out.
 
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