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Author Topic: "Flexible" Low Loss Coax?  (Read 6290 times)

KA1OWC

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"Flexible" Low Loss Coax?
« on: July 10, 2017, 12:29:31 PM »

Hi: I need a run of about 25 feet of low loss coax for satellite work that will be flexible enough to use portable (coil up easily)...I have heard that LW-400 is much too stiff for this...Could someone suggest an alternative? Thanks,

Steve KA1OWC
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Steve, KA1OWC
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KJ4HVL

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RE: "Flexible" Low Loss Coax?
« Reply #1 on: July 11, 2017, 05:51:23 AM »

LMR-400 Ultraflex may be usable, but at 25FT unless you are using absolute trash coax, or are attempting EME, the losses shouldn't be too bad. Even mini-8  at 7.9db per 100ft would only be 1/4 of that amount at 25ft (between 1.5 and 2dB of loss).

Keep in mind a 100' run of LMR-400 clocks in at 2.5dB of loss.

You could also consider an LNA pre-amp at the antenna end, at that point it is all kind of irrelevant since the system noise figure is dominated by the first element in the signal chain.
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N4UFO

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RE: "Flexible" Low Loss Coax?
« Reply #2 on: July 12, 2017, 01:33:40 AM »

With respect to KJ4HVL's figures, and despite the claims on some retailer's websites, the 'UF' versions of Times microwave LMR cable are NOT the same as the regular versions. At 450 Mhz, LMR-400 has 2.7 db/100' loss whereas LMR-400UF has 3.3 dB/100' loss. (Source, Times Microwave fact sheets:  https://www.timesmicrowave.com/documents/resources/LMR-400.pdf[url]]]https://www.timesmicrowave.com/documents/resources/LMR-400.pdf[url] https://www.timesmicrowave.com/documents/resources/LMR-400-UF.pdf[/url])

I would recommend, Davis RF Buryflex. http://www.davisrf.com/buryflex.php I use it between my mast mounted preamps and antennas and it has no problem with the flexing... it's stranded center conductor and has held up through several winters of twisting the beams up/down and around.

If you feel you MUST go with small coax, look at the Wireman's website http://thewireman.com/coax.html and consider #118. It's the same size as LMR-240UF, but less loss. (Same story applies... LMR-240 has slightly better figures, but LMR-240UF is not as good.)

At 25 feet, I'd recommend the Davis RF unless, as mentioned, you have preamps at the antenna, which would more than make up for the loss of smaller coax. I know when one looks at the dB loss charts, the math might suggest it shouldn't matter... but in practice, even a couple feet have been known to make a significant difference with some weak signal UHF downlinks, most notably SO-50. *insert anecdotal stories here* Bottom line, the SO-50 satellite is transmitting 1/4 watt to a 1/4 wave whip tumbling through space hundreds of miles up... it may not seem like it, but a small bit of extra loss can matter.

73 & GL!

Kevin N4UFO
« Last Edit: July 12, 2017, 01:56:31 AM by N4UFO »
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WA4SCA

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RE: "Flexible" Low Loss Coax?
« Reply #3 on: July 12, 2017, 05:42:39 AM »

A couple of years ago, I had to rebuilt my array, courtesy of a wind gust.  I have used 400UF as the "rotor loop" for years, but decided to go with 9913F.  It is significantly more flexible that 400UF, with similar loss characteristics and cost.  After 3+ years, no signs of electrical or mechanical deterioration. 
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W5PFG

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RE: "Flexible" Low Loss Coax?
« Reply #4 on: July 12, 2017, 09:48:13 AM »

I use LMR-240uf for all my portable satellite operations but mostly in 10' jumpers. Without any preamps, I can work any of the current satellites horizon to horizon. 

Out of curiosity, are you using 25 feet because you are going to have a mechanical rotor?
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KJ4HVL

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RE: "Flexible" Low Loss Coax?
« Reply #5 on: July 14, 2017, 05:25:06 AM »

With respect to KJ4HVL's figures, and despite the claims on some retailer's websites, the 'UF' versions of Times microwave LMR cable are NOT the same as the regular versions. At 450 Mhz, LMR-400 has 2.7 db/100' loss whereas LMR-400UF has 3.3 dB/100' loss. (Source, Times Microwave fact sheets:  https://www.timesmicrowave.com/documents/resources/LMR-400.pdf[url=http://]]https://www.timesmicrowave.com/documents/resources/LMR-400.pdf[url]]]]https://www.timesmicrowave.com/documents/resources/LMR-400.pdf[url] https://www.timesmicrowave.com/documents/resources/LMR-400-UF.pdf[/url])

I never cited a loss figure for UF, just plain old LMR-400 with respect to 8x, as in, a 25ft run of even low quality cable isn't so bad. In his setup (portable) with only 25' unless he is using like walmart ca-tv coax he shouldn't have much of an issue using just about anything laying around.
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N4UFO

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RE: "Flexible" Low Loss Coax?
« Reply #6 on: July 14, 2017, 06:57:14 AM »

KJ4HVL, agreed, you never cited a loss figure for the UF. But you started out by discussing LMR-400 Ultraflex and then you appeared to quote the loss figures for LMR-400... (I can't really be sure because you didn't specify the frequency for that figure.) The point I was trying to make is that many hams assume that the loss figures are the same for both versions which is erroneously promulgated by websites such as Universal Radio which quote incorrect figures for the Ultraflex version of the feedline. http://www.universal-radio.com/catalog/cable/coaxperf.html#atten  Simply attempting to educate about the incorrect information out there, not to embarrass or 'call anyone' regarding such.

The reason it's germane to my advice is because usually when I recommend the 9914F Buryflex or the Wireman #118 I am told that LMR-400UF or LMR-240UF (respectively) is 'better coax'. Well 'better' is subjective, but if they mean they are 'less loss', the manufacturer's figures disagree. They have slightly 'greater loss' at the desired frequencies and are also, in my observations, significantly more expensive (~30-50 cents a foot), which is why I prefer and recommend the 9914F and #118.

As for the rest... feedline loss on satellites is not unlike a discussion on the topic of UFOs. You have either experienced it for yourself or you haven't and no amount of discussion seems to sway people on the matter. So I've learned to steer clear of debates with regards to both discussions and I merely give my opinion to people when asked for it. That is, as far as satellite feedline is concerned. As for the other, let's just say that I've never seen a UFO...  but it's a big universe and I could have missed something and leave it at that. ;)  

73, Kevin N4UFO
« Last Edit: July 14, 2017, 07:05:02 AM by N4UFO »
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KJ4HVL

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RE: "Flexible" Low Loss Coax?
« Reply #7 on: July 14, 2017, 10:21:30 AM »

KJ4HVL, agreed, you never cited a loss figure for the UF. But you started out by discussing LMR-400 Ultraflex and then you appeared to quote the loss figures for LMR-400... (I can't really be sure because you didn't specify the frequency for that figure.) The point I was trying to make is that many hams assume that the loss figures are the same for both versions which is erroneously promulgated by websites such as Universal Radio which quote incorrect figures for the Ultraflex version of the feedline. http://www.universal-radio.com/catalog/cable/coaxperf.html#atten  Simply attempting to educate about the incorrect information out there, not to embarrass or 'call anyone' regarding such.

The reason it's germane to my advice is because usually when I recommend the 9914F Buryflex or the Wireman #118 I am told that LMR-400UF or LMR-240UF (respectively) is 'better coax'. Well 'better' is subjective, but if they mean they are 'less loss', the manufacturer's figures disagree. They have slightly 'greater loss' at the desired frequencies and are also, in my observations, significantly more expensive (~30-50 cents a foot), which is why I prefer and recommend the 9914F and #118.

As for the rest... feedline loss on satellites is not unlike a discussion on the topic of UFOs. You have either experienced it for yourself or you haven't and no amount of discussion seems to sway people on the matter. So I've learned to steer clear of debates with regards to both discussions and I merely give my opinion to people when asked for it. That is, as far as satellite feedline is concerned. As for the other, let's just say that I've never seen a UFO...  but it's a big universe and I could have missed something and leave it at that. ;)  

73, Kevin N4UFO

Understood, and appreciate the clarification. The loss stated was for the UHF side of the amateur satellite band. (Assuming nobody is using L/S right now). I've seen feedline loss cause issues before, but it was for deep leo's that had very high bit-rate radios for moving images. The site at which our GSE was located dictated a run of approximately 350' (was mountain top, and we needed to keep the shelter away from the lightning rod / anetenna array). Even with heliax we needed a mast-head pre-amp to pull out the signal.

As for my suggestion of lighter weight cable, OP wants to coil the lines and at 25' why not go light and cheap?
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N8HM

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RE: "Flexible" Low Loss Coax?
« Reply #8 on: July 14, 2017, 12:03:34 PM »

As for my suggestion of lighter weight cable, OP wants to coil the lines and at 25' why not go light and cheap?

Because the OP won't be able to hear the satellite. Even 5' of poor quality coax can cause "CHS Syndrome" for "Can't hear (squat)"

The math doesn't always tell the whole story. Never use poor quality coax if you want to work satellites. LMR-240UF is the absolute minimum I would ever consider. At 25', LMR-400UF is probably the minimum I'd ever consider.
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KJ4HVL

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RE: "Flexible" Low Loss Coax?
« Reply #9 on: July 18, 2017, 07:48:08 AM »

As for my suggestion of lighter weight cable, OP wants to coil the lines and at 25' why not go light and cheap?

Because the OP won't be able to hear the satellite. Even 5' of poor quality coax can cause "CHS Syndrome" for "Can't hear (squat)"

The math doesn't always tell the whole story. [snip]

Maybe poorly assembled cable can cause those issues, but math is math, physics and loss are very well defined, loss is a multiplier (divisor) applied to the system.

Sure loss raises the system temperature, but no, 5' of crap coax isn't going to trash your whole system (unless it was assembled poorly and has broken connections or shorts). If it would, arrow antennas wouldn't work (they actually don't work particularly well, but for other reasons), because the cable they use with their diplexers is about as cheap as it comes.

There is nothing wrong with higher loss cable as long as the run is kept short, especially if it suits the mission which OP requested flexible and portable.
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N4UFO

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RE: "Flexible" Low Loss Coax?
« Reply #10 on: July 18, 2017, 09:23:48 AM »

I know when one looks at the dB loss charts, the math might suggest it shouldn't matter... but in practice, even a couple feet have been known to make a significant difference with some weak signal UHF downlinks, most notably SO-50. *insert anecdotal stories here*

Anecdotal stories...

===

http://www.jerryclement.ca/HamRadio/VE6AB-Portable-OPS/i-nwqF8wQ/

http://www.jerryclement.ca/MachineShop/Antenna-Werks/i-sNNxBCL

http://www.jerryclement.ca/MachineShop/Antenna-Werks/i-7qxcsD6

looks like about 4-5 feet of cable, if that...

Observation:  "I noticed some loss in the signal"... enough that he felt the need to add a preamp.

Math: RG-58 loss @ 440 Mhz 10.4 dB/100' -- we're talking half a dB maybe? That's assuming 5 feet, so it may be even less.

And this from a guy with an awesome machine shop who builds antennas of all types on a regular basis, who's been all over Canada operating satellites and was even featured on the cover of an ARRL publication. He's not new to any of this...  http://www.jerryclement.ca/HamRadio/VE6AB-Portable-OPS/i-qgJp2Bw

===

I built one of those CJU antennas myself... just 3.5 inches of coax and mounted on top of my HT, it hears fine. But 2-3 feet of coax, not so much. These different feedlines were two ends of the SAME professionally manufactured jumper cut into two pieces. It was RG-174, math works out to less than a dB difference in the loss. I have been told repeatedly that less than a dB should not be noticeable in received signal strength... yet it was. I've been a ham for over 40 years... GROL, had 3-4 repeaters, maintained a network of packet sites; this is my second go on satellites.

===

A good number of experienced ops have been giving out this advice for YEARS to new sat ops making homebrew antennas... goes like this:

'Can't hear SO-50 with my new homebrew antenna.'

How much coax you have between it and radio?

'About 5-6 feet.'

Cut 2-3 feet off and try it again.

'I can HEAR it now!!!'

What kind of coax was it anyway?

'Some cheap crap I had laying around.'

Throw that out and get some better stuff.

'Absolutely!' <few days later> 'Hey you were right!'

These were most often new hams who were not biased by something they had read and listened to the hams with years of actual 'in the field' experience.

===

I still refuse to debate the topic, but I offer these anecdotal stories for whatever they may be worth to the OP and other readers. A person can believe them or not, makes no difference to me. One can also go try 5' of crap coax in the field and see if it makes an actual difference or not. But when 'I' spend my time and hard earned money to travel to a remote location to do expedition style sat ops, guess what... I'm taking only good quality coax. Even if I am deluded and wrong, I will feel better... BUT if I am right, the cost was relatively insignificant compared to what I spent on all other things (gas, meals, motels, etc). I would say the majority of experienced sat ops have learned this lesson already.

Which is my point to the OP, same point as N8HM and W5PFG I would assume... don't learn this lesson the hard way, go ahead and get the good stuff in the first place.

73, Kevin N4UFO
« Last Edit: July 18, 2017, 09:37:42 AM by N4UFO »
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KJ4HVL

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RE: "Flexible" Low Loss Coax?
« Reply #11 on: July 18, 2017, 01:54:55 PM »

No need to argue the point. We see things differently. Through simulation, and proper mission design, I've operated ground stations against Leo, Meo, SubOrbital (3 minutes, 1 time ever), and even Lunar Orbiting Satellites (LRO with a 21m dish no less), all with hardware that met the need for the specific mission some better quality than others.

On the suborbital mission we needed light coax that was easy to relocated, since the antennas were large and manually steered, and would need to be set-up and broken down repeatedly due to scrubs... No issue.

I've used arrow antennas with their garbage coax... No issue. For exercises with one of the cubesats I built (unfortunately splashed on Elana 1)

I will trust math, physics, and measurement any day to set my station up over some stories of questionable coax, that may have had any number of things wrong with it...

I agree, you get what you pay for, cheap coax can absorb water, have the dielectric crushed, have tin whiskers, or a hundred other problems that can contribute to issues. But it's going to be a lot easier to handle than ANY time-microwave product, and may suit the OPs mission better.


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N4UFO

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RE: "Flexible" Low Loss Coax?
« Reply #12 on: July 18, 2017, 05:23:40 PM »

No need to argue the point.

Agreed. So then why are you arguing the point? I've made my statements. Again, I don't debate this topic... because just like with the UFO debate, all the scientific minds can seem to come up with is, 'Don't believe you lyin' eyes!' (Although I suppose it's lyin' ears in the case of satellites.)

Movin' on...  :)
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KJ4HVL

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RE: "Flexible" Low Loss Coax?
« Reply #13 on: July 19, 2017, 08:55:25 AM »

No need to argue the point.

Agreed. So then why are you arguing the point? I've made my statements. Again, I don't debate this topic... because just like with the UFO debate, all the scientific minds can seem to come up with is, 'Don't believe you lyin' eyes!' (Although I suppose it's lyin' ears in the case of satellites.)

Movin' on...  :)

Not arguing my point, just including my anecdote, much as you. 73's
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