RG6 Vs RG8 together

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dwayne0564

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Going to run about 75-90 of Cable for a Base scanner I have about 50 feet of RG8 and about run it with a Tram 1040 discone antenna. will having RG6 and RG8 together, or should I get more of the RG8. suggestions.
 

trentbob

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Going to run about 75-90 of Cable for a Base scanner I have about 50 feet of RG8 and about run it with a Tram 1040 discone antenna. will having RG6 and RG8 together, or should I get more of the RG8. suggestions.
RG8 is definitely not your choice at 50 ft. But the RG6 certainly is satisfactory.

I don't know but, speaking for myself if I had the outdoor antenna setup and I'm not sure what you're listening to but if you're going to be going into the 7 and 800 megahertz range I would just go ahead and spend the few extra bucks for 50 ft of LMR 400.

Depends what your needs are and what you can afford.
 

prcguy

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When I look up the loss of good quality RG-8 I'm getting about 3.2dB loss for 50ft at 800MHz. For CATV type RG-6 its about 3.0dB loss depending on brand for 50ft at 800MHz. If your radio and antenna are 50 ohm using RG-6 will run the loss up more than RG-8. If the antenna and radio are rated at 50 ohm then I would choose RG-8 or LMR400 and leave the RG-6 to the TV guys.
 

Arkmood

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will having RG6 and RG8 together, or should I get more of the RG8. suggestions.
Wouldn't use RG6/8 together. One or the other.

1.LMR400 best choice of the three mentioned - you pay for it.
2.RG8 my 'go to' cable for long runs at vhf hi/uhf/700/800 - A real animal, can be hard to work with but worth the effort. Kick myself for selling all my 50ft rolls.
3.RG6 Good/Low Cost - Used at times, never did buy the 75ohm doesn't matter.
 

vagrant

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I agree with prcguy

but...

For two instances I use 75 ohm coax with 50 ohm receivers. I know there is additional loss due to the mismatch, but I'm mostly monitoring nearby stuff that's going through repeaters and my coax run is 50'. Additionally, those repeaters are anywhere from 100 ~ 5000' above my location. Thus, the signal loss is not an issue for me, but it would be a terrible choice for many others. If I were trying to monitor low power simplex or distant transmissions, 50 ohms all the way (antenna, coax, to receiver) would be the choice as well as using LMR-400 coax at a minimum.

Additionally, 50 ohms all the way is the choice for my military air scanner. From antenna, to coax, to radio it is 50 ohms, but I am trying to "hear" as far away as possible.

Everyone's situation and needs are different. I say use what you have on hand and if you're hearing everything you want to hear, you're good.
 

n5ims

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One thing that isn't clarified is that RG-8 is a very wide range of coax types. Are you talking about RG-8X (designed for moderate power HF work to be light so a wire antenna isn't weighted down by the heavy coax, but works poorly on higher frequencies).? Are you talking about 8237 (standard coax with a Are you talking about 9913 (double shield coax with a 90% coverage shield over a foil 100% coverage shield, 10 gauge solid center, semi-solid core and good for high power HR and better for VHF and UHF frequencies on reasonable runs)? Are you talking about 9913-F7 (double shield coax with a 90% coverage shield over a foil 100% coverage shield, 10 gauge solid center, foam core and good for high power HR and better for VHF and UHF frequencies on reasonable runs with a bit lower loss than standard 9913)? Are you talking about 9914 (double shield coax with a 95% coverage shield over a foil 100% coverage shield, 10 gauge solid center, foam core and good for high power HR and better for VHF and UHF frequencies on reasonable runs with a bit lower loss than 9913)? And the list goes on and on and on. Even LMR-400, RG-213, and RG-214 are RG-8 variants since generic RG-8 is simply a style of coax that is about 1/2" thick (RG-8X aside) with nominal impedance of 50 ohms.
 

Ubbe

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Instead of speculating I did some actual measurements.

I calibrated a VNA analyzer with a 50 ohm load and then connected it directly to a Uniden HP-1 by an adapter without any coax. The scanner where set to 800MHz and the impedance where sweeped over a 700-1000MHz range.

Then I used a 2ft 50 ohm RG174 coax and calibrated that with a 50 ohm load and sweeped the HP-1 using that coax.

Then I finally used a 75 ohm RG6 coax at about the same lenght but I cannot calibrate that. It has a much better velocity factor, 88 to 66 for RG174, so probably should have been 30% longer. But it is what it is.

The scanner doesn't have a constant 50 ohm impedance over its frequency range, no scanner has that. The analyzer seems to like the 75 ohm coax the best, but it's probably a fluke that the lenght of the coax somehow became the optinmal one. There are different factors that will influence scanners reception but the difference between 50 and 75 coax isn't a major issue.

I include sweep of a 5/8 GP antenna for 125MHz that shows how much its impedance fluctuate. Most antennas will show the same pattern, except discones and logperiodic that doesn't flucuate as much in its impedance.






/Ubbe
 
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