Coax Question

[blueline_308]

First, let me say that I have searched here and after reading pages of posts, still haven't quite got my answer, so....

I want two lengths of coax, 60 feet each with a male F connector -> male BNC on one of them and male F -> male F on the other. I dont want to use any adapters, so LMR400 is out, plus that stuff is just a litlle too rigid for me....I have used it before, and although its great cable, I feel that by the time you use the adapters, it kinda defeats the purpose of using it...so my question is....

Which coax would you recomend based on my desires....I want it to be good from VHF Lo to 800 MHz....and which on-line retailer would you recommend to buy from that will terminate it as I wish?

Thanks in advance for your help,

Jim

 

[DPD1]

I think the problem you'll run into is that you're trying to match a typical RG8 radio application type cable, to an F TV type connector. So if you have to use an F, you're pretty much limited to RG6 and 59. I don't believe I've ever seen an F made for an RG8 size. They DO have RG8 size cables in a 'flexi' version, which would help solve your problem of difficulty in handling. It's basically a version that has a multi wound center conductor instead of a single conductor, which makes it more flexible. I think the 9913 version is called 9913F, but I'm not positive. So you would probably want to go all 75 ohm and use a cable compatible with Fs, or somehow get away from the Fs... Which is what I'd do if possible.

Dave
http://www.dpdproductions.com
- Custom Scanner, Aviation, MURS, GMRS, Marine & Ham Antennas -

 

[N_Jay]

First, let me say that I have searched here and after reading pages of posts, still haven't quite got my answer, so....

I want two lengths of coax, 60 feet each with a male F connector -> male BNC on one of them and male F -> male F on the other. I dont want to use any adapters, so LMR400 is out, plus that stuff is just a litlle too rigid for me....I have used it before, and although its great cable, I feel that by the time you use the adapters, it kinda defeats the purpose of using it...so my question is....

Which coax would you recomend based on my desires....I want it to be good from VHF Lo to 800 MHz....and which on-line retailer would you recommend to buy from that will terminate it as I wish?

Thanks in advance for your help,

Jim

First adapters don't have that much loss unless you use sh!tty ones.

Second are you TX/RX or RX only?

 

[zguy1243]

RG-11- very good numbers and you can put F's right on this stuff. Just about the same numbers as LMR400

 

[gmclam]

RG-11- very good numbers and you can put F's right on this stuff. Just about the same numbers as LMR400

RG-11 is the wrong impedance. Use RG-8. "Just about the same numbers" is NOT the same numbers.

That coax which is flexible does not accept F connectors very well. F connectors are designed to be used with a single solid core.

Personally; I'd just just BNC (or SMA) connectors, and adapters where they are needed. I would not take F connectors seriously. I'd rather have a BNC on the end of my cable, use an adapter to F to connect to a device, and an adapter to convert back on the other side. But that's just me. As someone pointed out, just use GOOD quality connectors, and the loss is minimal. (there is some loss with F connectors too)

Use the LMR400 except for the last 10 feet, so you have the flexibility.

 

[zguy1243]

RG-11 is the wrong impedance. Use RG-8. "Just about the same numbers" is NOT the same numbers.

Do you think that the impedance of the receiving system stays at 50 ohms over the hundreds of Mhz that new scanners cover?

RG11 has better Db per 100ft loss figures than RG-8.

RG-11 IS VERY close to LMR400 in the numbers, in the tenths of a db, Not noticable.

It accepts a F connector,they are made for this coax, this is what he was looking for. And I guarantee it will outperform Rg8 anywhere above 400Mhz. Thats were the difference is noticable.

 

[blueline_308]

Do you think that the impedance of the receiving system stays at 50 ohms over the hundreds of Mhz that new scanners cover?

RG11 has better Db per 100ft loss figures than RG-8.

RG-11 IS VERY close to LMR400 in the numbers, in the tenths of a db, Not noticable.

It accepts a F connector,they are made for this coax, this is what he was looking for. And I guarantee it will outperform Rg8 anywhere above 400Mhz. Thats were the difference is noticable.

Thats the info that I was looking for....which coax natively accepts F connectors...forgive me if I wasn't specific enough. Now, which RG11....I have seen many different versions or part numbers I should say...so which would you consider the best for RX only and maybe recommend an on-line source for it with the connectors F male --> F male installed.

Thanks to everyone

 

[zz0468]

First adapters don't have that much loss unless you use sh!tty ones.

I agree 1000%. What's with this irrational fear of adapters that people here have? Under 1 GHz, it takes a $100,000 instrument to even see that they're there.

 

[N_Jay]

I agree 1000%. What's with this irrational fear of adapters that people here have? Under 1 GHz, it takes a $100,000 instrument to even see that they're there.

You are agreeing too strongly.

It only takes about $2000 of the equipment if you know what the "F" you are doing.

But that takes us back to the heart of the problem; Most people don't, yet they think they do!

 

[zz0468]

True enough. But I HAVE the $100,000 instrument. I don't have the $2000 one. A TDR would show the bump, the network analyzer shows what the bump REALLY looks like.

 

[gcgrotz]

Me to me too. I can see adapters and connectors with my analyzer and it cost $3300. But yes, below 1GHz it is pretty much a non-factor with good adapters. And unless you are trying to wring out every last tenth of a db at 800 MHz (which you won't hear anyway) I'd just use good RG8-x, its flexible and easy to put connectors on and you won't have the cable trying to pull your scanner off the table like the big stuff will do.

One of these days someone should make a recording of a weak signal and then add 3db so everyone can hear what they're agonizing over. Maybe this weekend.

 

[tonsoffun]

I agree with you guys, but I myself would like to have the proper connector on the end of your coax rather then having all these bulky connectors connected to your equipment. But sometimes you will not find the connector for your type of coax, In our perfect world I guess.
Take care

 

[blueline_308]

OK, now that the adaptor horse has been beat to death, can someone reply to part of my original request....a recomendation of an on-line source for good RG!! for RX that will come with connectors?

 

[gmclam]

Adapters - LOL

I am amazed in reading through the comments here. Most of my problem comes from too much signal (from an outside antenna) and not too little. So my connections are:
ANTENNA - SO-239{ {PL-259----(RG-8)---PL-259} }SO-239 to BNC} }FILTER} }BNC to F} }F---(coax)---F } }SPLITTER{ {F---(coax)---F} }F to BNC} }BNC RIGHT ANGLE} }SCANNER

Not only am I using adapters, I have that right angle adapter in there so the cable does not have to go "straight down" into the scanner.

I too would like to know where to get some good cable. I would like to make another run or two to additional scanners.

 

[DPD1]

OK, now that the adaptor horse has been beat to death, can someone reply to part of my original request....a recomendation of an on-line source for good RG!! for RX that will come with connectors?

A customer pointed these guys out to me the other day... They appear to have numerous pre-made cables to choose from. I've never dealt with them though.

http://www.hyperlinktech.com/web/cable_feed400.php

There's also www.thewireman.com which will do cables with custom connectors if you contact them. It's good stuff for reasonable prices.

Dave
http://www.dpdproductions.com
- Custom Scanner, Aviation, MURS, GMRS, Marine & Ham Antennas -

 

[OpSec]

Do you think that the impedance of the receiving system stays at 50 ohms over the hundreds of Mhz that new scanners cover?

Yes. Feedline impedance is not a function of frequency, as it relates to general scanning between 30-1000 MHz with a scanner. The feedline and antenna system should be either all 50 ohm or all 75 ohm, not a haphazard mixture of both. Sure, there may be some impedance changes based on length of feedline, type of antenna connection, etc but if everything is put together right the impedance will not bounce around too much.

One of these days someone should make a recording of a weak signal and then add 3db so everyone can hear what they're agonizing over. Maybe this weekend.

Amen!

 

[N_Jay]

I agree with you guys, but I myself would like to have the proper connector on the end of your coax rather then having all these bulky connectors connected to your equipment. But sometimes you will not find the connector for your type of coax, In our perfect world I guess.
Take care

Scrap the adapter and use a flexible jumper.

Fixes the connector and cable issues all in one step.

 

[N_Jay]

Yes. Feedline impedance is not a function of frequency, as it relates to general scanning between 30-1000 MHz with a scanner. The feedline and antenna system should be either all 50 ohm or all 75 ohm, not a haphazard mixture of both. Sure, there may be some impedance changes based on length of feedline, type of antenna connection, etc but if everything is put together right the impedance will not bounce around too much.

The issue is that the feed-line to antenna match IS frequency dependant.

Over the range you are typically scanning, the antenna impedance is all over the place, so the difference between 50 ohm and 75 ohm is IRRELEVANT.

I don't thing anyone was suggested mixing cable types. (and even that would not really matter much.)

 

[tonsoffun]

Scrap the adapter and use a flexible jumper.

Fixes the connector and cable issues all in one step.

Exactly Right N-jay, That is why I am starting to provide these cables for people that need little jumper cables with proper connectors.
Take care

 

[dbox1]

My suggestion is relatively the same as Bob Grove's take on it. Quad shield RG6 of good quality will give you very good performance throughout the spectrum. When you begin to transmit on a single band of frequencies, then matching for low SWR is more critical, but reception over such a broad set of bands will not be greatly affected by choosing one over the other in either 50 or 75 ohm feeder. My leadin of choice for scanners is Belden 1189A.