Jump to content
foliver

good 50 ohm cable for remote antennas?

Recommended Posts

Hello all.

I need to buy a bit of coaxial 50 ohm low loss cable for my shark fins.

I prefer the soft cables, and light ones.....

Someone has a good one to recomend?

Thanks a lot!

 

Fabian

Share this post


Link to post
Share on other sites

This is a bit random as they aren't really known but I've been having some nice BNC cables made by "American Coaxial Industries" who you can contact and order custom stuff or they have a ton listed on their ebay store (seems they are based on the outskirts of Los Angeles).  So far I've had some BNC to BNC timecode cables and a couple of antenna SMA to BNC from them and they seem to be holding up well?  Mileage will vary as I haven't put them through the extremes yet considering I only started buying from them a couple months before the pandemic hit but they survived a few weeks in rural Africa on a rather challenging set so so far so good...

https://www.ebay.com/str/americancoax1

 

Share this post


Link to post
Share on other sites

Just a reminder: Loss per foot is inversely proportional to cable diameter. There is no magic that will give you a low loss, small diameter cable even if the cable is made from unobtainium.

Best Regards,

Larry Fisher

6 hours ago, foliver said:

Hello all.

I need to buy a bit of coaxial 50 ohm low loss cable for my shark fins.

I prefer the soft cables, and light ones.....

Someone has a good one to recomend?

Thanks a lot!

 

Fabian

 

6 hours ago, codyman said:

This is a bit random as they aren't really known but I've been having some nice BNC cables made by "American Coaxial Industries" who you can contact and order custom stuff or they have a ton listed on their ebay store (seems they are based on the outskirts of Los Angeles).  So far I've had some BNC to BNC timecode cables and a couple of antenna SMA to BNC from them and they seem to be holding up well?  Mileage will vary as I haven't put them through the extremes yet considering I only started buying from them a couple months before the pandemic hit but they survived a few weeks in rural Africa on a rather challenging set so so far so good...

https://www.ebay.com/str/americancoax1

 

 

 

Share this post


Link to post
Share on other sites
11 hours ago, BAB414 said:

I swear by ultraflex:

 

https://fieldcomponents.com/LMR-240-UF-UltraFlex-Cable-Assemblies-Times-Micro.html

 

Make sure you get the 240. Anything higher is stiff and thick.

Two points:

1. RG-8x is not equivalent to RG-8, a much larger cable with lower loss.

2. The LMR-240 is an improved RG-58 equivalent with 7 dB loss/100 feet. It is not as low loss as RG-8 or Belden 9913F, both 0.400" cables.

Best Regards,

Larry Fisher

Edited by LarryF
changed feet ' to inches "

Share this post


Link to post
Share on other sites

I would only do LMR-240-UF for short runs. Like 15’ up the antenna mast. RG8x is the same stuff minus the foil shield so it’s more flexible and lays more flat. Better for long runs where you’re amplifying at the antenna. 
 

Belden 9258

Share this post


Link to post
Share on other sites
58 minutes ago, Derek H said:

I would only do LMR-240-UF for short runs. Like 15’ up the antenna mast. RG8x is the same stuff minus the foil shield so it’s more flexible and lays more flat. Better for long runs where you’re amplifying at the antenna. 
 

Belden 9258

Just speaking from personal experience...

The ultra flex is...ultra flexible (the 240 version!). And I regularly do 100' runs on it with powered fins and it's never let me down.

Share this post


Link to post
Share on other sites

Are you talking about the times microwave brand stuff? If so, the stuff I got, ordered from DX engineering, was a noticeable amount stiffer than Belden 9258. (RG8x) You could certainly use it for long runs but I found that sticking with RG8x was my preference. The LMR240UF definitely seems like a much better shielded cable than RG8x. I also chose to use the ultraflex for short jumpers inside my cart where god knows what kind of EM is flying around.

The other nice thing about Ultra Flex and Belden 9258 is you can use the same model Amphenol BNC on either one.

Share this post


Link to post
Share on other sites
40 minutes ago, Derek H said:

Are you talking about the times microwave brand stuff? If so, the stuff I got, ordered from DX engineering, was a noticeable amount stiffer than Belden 9258. (RG8x) You could certainly use it for long runs but I found that sticking with RG8x was my preference. The LMR240UF definitely seems like a much better shielded cable than RG8x. I also chose to use the ultraflex for short jumpers inside my cart where god knows what kind of EM is flying around.

The other nice thing about Ultra Flex and Belden 9258 is you can use the same model Amphenol BNC on either one.

I am.

 

All I know is, it works. It's something I was looking for for a long time. Lot's of people these days are talking about remoting their receivers because of social distancing on set, etc and they're going all dante and cat5/6. I've lived that life as well but ultraflex makes remoting antennas over long distances a breeze, especially with the newer powered antennas. Less gear I have to worry about being too far away from me, direct control and sight of my receivers, and same (or very similar) results.

Share this post


Link to post
Share on other sites

Thanks all for your replies, and information!

 

BAB414, what shark fins are you using?

 

How many feet run you can do without using powered antennas?, i know it's a difficult question, but ...

 

Thanks again!!

 

Share this post


Link to post
Share on other sites

My new setup is 10 feet of ultraflex 240 with ALP620 passive fins (just switched over from 15 feet of RG-8x - not for increased performance, I just wanted shorter custom cables so I figured I'd go with them). If I need to get them around a corner, I've been switching to 25 feet of RG-8x (that's just what I have). Anything more, I switch to my Shure UA874 active fins with the 100ft ultraflex with the antennas at +6 gain. Been doing it like this for a 2-3 years with antennas going straight into the Venue 2. I just added the aforementioned 10 ft ultraflex installation for the cart and a small patch bay with 2 feet of cable between it and the Venue for quicker antenna switching. What's also cool is that the ALP620's are passive but sending them power doesn't do any harm, so I can just leave the power setting on in the Venue so that's one less step to worry about.

 

I haven't tested the limits of passive fins with ultraflex but I calculate about 6dB of loss over 100ft (Larry says 7 so I'd go with that figure).

 

Lectro and Wisy have some very cool looking antennas where you can dial in exactly how much gain you want and attenuate. I think these are ideal. Especially having two sets so you can quickly switch over without dismantling your cart.

 

Something to be aware of for any cable, especially skinny ones, if they get scissored in a door, you're gonna have a bad time.

Share this post


Link to post
Share on other sites
1 hour ago, BAB414 said:

[snip] I haven't tested the limits of passive fins with ultraflex but I calculate about 6dB of loss over 100ft (Larry says 7 so I'd go with that figure). [snip]

 

The 7 dB number is for the upper frequency end (600 MHz+) of U.S. frequencies. If you are at the lower end (500 MHz) 6 dB is correct.

Best,

LEF

Share this post


Link to post
Share on other sites

After talking to Karl W, I'm considering getting 3dB passive gain attenuators because I'm worried I'm coming in too close to 0, but other than the normal NYC problems I'm used to (crowded spectrum etc), I've had great performance.

Share this post


Link to post
Share on other sites
2 hours ago, BAB414 said:

After talking to Karl W, I'm considering getting 3dB passive gain attenuators because I'm worried I'm coming in too close to 0, but other than the normal NYC problems I'm used to (crowded spectrum etc), I've had great performance.

What problem are you trying to solve with 3 dB attenuators?

LEF

Share this post


Link to post
Share on other sites
42 minutes ago, LarryF said:

What problem are you trying to solve with 3 dB attenuators?

LEF

The theoretical problem of overloading the receiver with RF. I haven't had any issues, but Karl's video Best RF Practices opened my eyes to correctly dealing with signal loss and compensating with gain. My understanding is that sharkfin antennas (active or passive) natively have 4 dB of gain. If I run 100 feet of LMR240-UF, I lose about 6dB, which means the RF signal hits the receiver at -2dB (if I don't add/subtract any gain from the antenna). I'm under the impression that -6 - -2 dB is the sweet spot because you don't want to overload. Would love to hear your thoughts.

Share this post


Link to post
Share on other sites

Let me clarify some points. Gain from a directional antenna is different from the gain of an amplifier. An amplifier gains up both the desired signal, in band but undesired RF signals, and any undesired noise. Too much of this amplifier gain can upset the squelch circuits, diversity system, sliding filters (Lectro) and other parts of the receiver system. By too much gain, we are speaking of more than say a total 6 dB of amplifier gain after cable losses. Since off frequency signals may also be gained up by the amplifier, intermod can also increase.

 

Antenna gain is a horse of different feathers. Antenna gain is directional gain and is largely noiseless in the sense that the desired signal may increase but undesired signals (noise floor) are largely rejected by the amount of gain of the antenna and background noise is reduced too, i.e., an antenna with 4 dB of directional gain increases the desired signal by 4 dB but the noise floor does not increase. If an interfering signal is in the null of an antenna, you would get even more rejection. 

 

In sum, don't attenuate the gain (directional antenna gain) of a passive antenna. Do attenuate amplifiers for active antennas at the receiver end of your cabling if you have excess gain of say 5 dB or more. Excess gain is the amplifier gain minus cable losses and splitter losses.

 

Finally, it is hard to overload the inputs of modern receivers with a desired signal due to robust front ends and AGC (Automatic Gain Control) in digital receivers. However, gaining up the noise floor can cause problems as discussed above.

 

The final comment  => You don't need a 3 dB attenuator.

Best Regards,

Larry Fisher

 

Share this post


Link to post
Share on other sites

LDF-5 1db loss per hundred feet at 600MHz.  Great for fixed installations, but a bear on location!!  

Share this post


Link to post
Share on other sites
15 hours ago, LarryF said:

Let me clarify some points. Gain from a directional antenna is different from the gain of an amplifier. An amplifier gains up both the desired signal, in band but undesired RF signals, and any undesired noise. Too much of this amplifier gain can upset the squelch circuits, diversity system, sliding filters (Lectro) and other parts of the receiver system. By too much gain, we are speaking of more than say a total 6 dB of amplifier gain after cable losses. Since off frequency signals may also be gained up by the amplifier, intermod can also increase.

 

Antenna gain is a horse of different feathers. Antenna gain is directional gain and is largely noiseless in the sense that the desired signal may increase but undesired signals (noise floor) are largely rejected by the amount of gain of the antenna and background noise is reduced too, i.e., an antenna with 4 dB of directional gain increases the desired signal by 4 dB but the noise floor does not increase. If an interfering signal is in the null of an antenna, you would get even more rejection. 

 

In sum, don't attenuate the gain (directional antenna gain) of a passive antenna. Do attenuate amplifiers for active antennas at the receiver end of your cabling if you have excess gain of say 5 dB or more. Excess gain is the amplifier gain minus cable losses and splitter losses.

 

Finally, it is hard to overload the inputs of modern receivers with a desired signal due to robust front ends and AGC (Automatic Gain Control) in digital receivers. However, gaining up the noise floor can cause problems as discussed above.

 

The final comment  => You don't need a 3 dB attenuator.

Best Regards,

Larry Fisher

 

Thanks Larry. This is helpful and actually makes sense. I didn't think I needed attenuators but wanted to experiment because my (flawed) math wasn't in line with my real world experience (which has been good!). I thought all RF "gain" was the same. Had no idea. There's no way I'm ever coming close to +5dB so I'm going to keep truckin' as I have been! Really appreciate what you and Karl have taught me. Love Lectro!

Share this post


Link to post
Share on other sites

Belden 9258. It’s an RG-8X. Coils very nicely, feels like a 75ohm video bnc and has reasonable loss. I carry two that are 115’ each which is 10.5db loss at 500mhz and 11.5db at 600mhz. Seems to be a perfect length for remote fins. The short cables with passive fins don’t really matter as much. 
 

I’ve used the cables with Lectro ALP650 and Wisycom LFA shark fins. Seems great with both. 
 

Gotham built the cables for me. 
 

also:

 

https://www.qsl.net/co8tw/Coax_Calculator.htm

Share this post


Link to post
Share on other sites
11 hours ago, foliver said:

Thanks Larry and all for the contribution to this thread, i've learned a lot !

 

Fabian


I think it's time for Larry to write his memoir/technical reference 

"Tumbleweeds and Transmitters" 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...