Choice of cables for serious antenna systems

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Choice of cables for serious antenna systems

Postby vk3six » Sat Dec 26, 2009 9:46 am

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Re: Choice of cables for serious antenna systems

Postby VK4TS » Sat Dec 26, 2009 10:13 am

Steve,

Some things to consider...

LMR400 (and its relatives) is available from Rojone reasonably cheap http://www.rojone.com.au .........with the reference to burying.. I pulled down an old system running LMR400 that was in very good order after 10 plus years..this has gained huge popularity in the US in contest circles..there is also a flexible version but I have never tried it...usually use fly leads of RG213..

Open wire or 450 ohm could be considered...especially with the cancellation properties that would minimise RF interference between 10 and 6 M with http://www.ocarc.ca/coax.htm it shows the losses better than LDF550...but you need to remember additional conversion losses inside any baluns or rf choke..(50 to 450)

or scrounge around and see what you turn up...we used 80 M of LDF550 on a repeater we installed a few years ago that was literally on its way to the tip...brand new on a roll !!!!
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Re: Choice of cables for serious antenna systems

Postby VK4GHZ » Sat Dec 26, 2009 10:47 am

Steve, a timely topic.

How long a run are we talking here?
That will dictate everything.

I am actually sitting here preparing a new run of LMR400 to get the JHV back up on the tower.
The LMR400 will be the patch from D.E, down the boom, around the rotator to the existing LDF4-50 running up the tower.

This grotty old LDF4-50 bothers me.
It was second hand to begin with, purchased from the Ballarat Hamfest in 1997, and has the usual ever increasing number of nicks and kinks in it.
What really bothers me, is what you cannot see on the inside.

I'm inclined to replace this LDF4-50 with a fresh run of new LMR400.
Connectors for Heliax are an expensive pain in the bum.
N-Connectors are cheap and easy to fit to LMR400.
The Jyebao LMR400 from the RF Shop has 0.95dB loss / 100 ft length at 50MHz.
It is also much lighter and easier to manage than LDF4-50.

You reach the point of diminishing returns, and at what expense?
The extra 0.2 - 0.3dB feedline loss (of LMR400) with the 20M run here would be less than the expected variation between one IC-7600 and another off the assy line.
Keep it real.
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Re: Choice of cables for serious antenna systems

Postby VK2AAH » Sat Dec 26, 2009 11:53 am

Hi all,

I've been involved in a lot of radio network roll-outs over the years and still strongly lean towards LDF4 or LDF5 for reasons of life span. In recent years I've seen an increased use of LMR400 but LDF is still overwhelmingly the preferred cable. I've recently inspected some installations that I supervised with Norm Deitch doing the cable work, and after 10 years the cable still looks to have another decade of life left in it. Modern LDF4 connectors are far easier to fit, with the proper drill accessory, and fitted properly very rarely fail. I also believe that the price of LDF4 has dropped significantly in recent years, relative to other types of feeder. You get what you pay for with cable as in anything else- the determining factor is the copper & now alumium content.

I have a general rule with managing cable loss at UHF- LDF4-50 up to 50m, above that LDF5-50 or equivalent.

And if you think these are a pain, try LDF7-50.

Regards,


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Re: Choice of cables for serious antenna systems

Postby VK5PJ » Sat Dec 26, 2009 1:05 pm

Hi Adam et all

VK4CP wrote:Steve, a timely topic.
This grotty old LDF4-50 bothers me.
It was second hand to begin with, purchased from the Ballarat Hamfest in 1997, and has the usual ever increasing number of nicks and kinks in it. What really bothers me, is what you cannot see on the inside.


Do not be concerned about not being able to see inside the LDF series of cables (ANDREW or RFS), the foam inner is a 'closed cell' and moisture can NOT proceed past a few millimetres of the exposed end. If in doubt cut one end back by 30mm and reterminate it, it will all look like NEW.

I had moisture in a run of LDF5-50 about 2 years ago (144 MHz yagi) and originally had similar fears but when I pulled the connector off, the water was just on the top of the foam and a simple wipe with a rag removed it, I then let the exposed end sit in the sun for a day or two before putting the connector back on. Result is just fantastic, VSWR problem gone and a quick cable loss measurement on 144 MHz showed it to be on spec.

Your biggest enemy with the LDF series is where the corrugations get flattened, giving you impedance issues. I have two nice LDF4-50 runs here I bought in a similar way to you BUT mine had large flat spots along the cable (YUK).

The LDF series will probably out last most HAM's if treated with respect and the outer jacket will present quite a challange for the average bird. I run all my antennas upside down so the feeder is under the boom and where possible use stainless steal straps fastened relatively loosely (so as to not crush the cable) then PVC tape to finish of the cocktail.

Now back on the original subject, I have RG-213 tails on the yagis and then come down to the rotator.. from here on its a mixture of Times LMR400 and LDF5-50 to the shack (depends on the band) I have some new LMR400 Ultra flex to replace the RG-213 when I next do antenna maint, it would seem to be a great choice for above the rotator and as Trent said, easy to get from Rhojone.

Steve, I have a stock of Andrews connectors for LDF4-50 so let me know what you need (most are new N Females)
Yikes enough of my rambling.
Regards
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Re: Choice of cables for serious antenna systems

Postby VK3ALZ » Sat Dec 26, 2009 1:37 pm

I think LDF4-50 is very hard to beat for runs that don't flex.
The matching Positive Stop connectors are very easy to fit even without the $400.00 Andrew tool.
Everything comes at a price and I firmly believe you get what you pay for.

I see Andrew (CommScope) are stopping production of LDF5 and LDF6....

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Re: Choice of cables for serious antenna systems

Postby VK4CZ » Sat Dec 26, 2009 1:48 pm

Current 6m yagi is fed with LDF4-50 (30m run) with a 9913 tail (10m), and new 6M2WLC is being fed with LDF5-50 (80m run) with LMR400 tail (~25m) and wouldn't consider anything else nowdays.... my 20m 5el monobander is also fed with LDF4-50, as will the new 10m 5 el :P

Not 100% sure it can be purely attributed to the coax feedlines as my location and antennas certainly help, but I hear far better than many of the stations within a 10km radius of me reagrdless of band so it certainly assists. :D
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Re: Choice of cables for serious antenna systems

Postby VK2XSO » Sat Dec 26, 2009 7:50 pm

I'm not sure what the ham fascination with LDF4 and LDF5 is.
LDF1-50 and FSJ1-50 do a fantastic job and they are cheap(er) and flexible, low loss and the diameter not much bigger than RG58.
The price for this cable and connectors new is affordable directly from Andrew.
I often wonder if clubs have considered ordering a larger rolls of it and bulk connectors to make the price even cheaper for their members.

LDF2 and FSJ2 series are slightly bigger. About the diameter of RG213, offer slightly better performance, but still nice and flexible.

Hams typically have very deep pockets but very short arms.

Used heliax connectors can be found around vk2 flea markets for ~$2 each. They're easily dressed and reused as good as new.
Heliax coax is also easy to find. There are many scrap dealers who recover it and if you get to know which ones, you can buy recovered
heliax or similar RFS cable by the kilogram at copper price.

A few of the scrappies cotton on the the value of the cable and attempt to charge more for it. That is when you have to walk away and come back next week.
It costs them time and money and pollution to strip out the copper. They're making a very good clean profit at bullion price for something that is almost half plastic by weight.

On a strange note I often hear some hams talk about not being able to use LDF4/5 because they would have to use a tail at each end.
It's then I hear one of my favourite ham myths. 1dB loss per connector or 1dB loss per connection. I can't help but laugh.
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Re: Choice of cables for serious antenna systems

Postby VK2AAH » Sat Dec 26, 2009 8:28 pm

Hi Trent,

I'm not going to argue with you if you are saying that many use far heavier grade of feeder than they really need- I see it often at land mobile bases where LDF5-50 is used at 80MHz on a 20m run. Sadly people don't understand loss, instead choosing to waste money where no benefit can be gained.

But VK3SIX asked about 200ft runs up a tower for 6m & 2m- hardly a job for LDF1! That is the kind of job LDF4 in particular was made for.

Cheers,

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Re: Choice of cables for serious antenna systems

Postby vk3six » Sun Dec 27, 2009 6:46 am

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Re: Choice of cables for serious antenna systems

Postby VK2AAH » Sun Dec 27, 2009 7:31 am

Steve,

Are there any friendly hams around that have contacts with riggers doing any system upgrades? There must be someone around replacing feeders or stripping down towers? We usually end up throwing out our old LDF4-50 even though it is still perfectly useable (no nicks or kinks) because no-one wants it. People like John Bennett at Shep might know where to look if he doesn't have any old stuff himself.

I was thinking you might need some cable ties while you are at it! It does look like a bit of a rats nest, doesn't it!

Cheers,


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Re: Choice of cables for serious antenna systems

Postby VK5ZK » Sun Dec 27, 2009 8:58 am

I am surprised that no-one has considered actually measuring the loss in their feed line before installation. Most would have the tools to do this with adequate accuracy. All that is needed is a good dummy load and a reasonable quality power meter. Measuring the power at each end of the cable with the dummy load installed should give a feeder loss reading and verify what the spec sheets say the loss should be. I do this EVERY time I make a new cable.
Slightly off topic but relavent was a test I did with right angle N type M-F fittings a while ago. I had 4 to use on 2mx on a power splitter and preamp so I joined them all together and inserted them in my 1.2ghz feeder before the power meter. The difference in power reading was negligible. No problem on 2mx then.

The purists may pick holes in this technique but it seems valid to me.

Assuming your feedline is of good standard the issue of spacing of antennas of different bands on the same mast, especially having a HF yagi well inside the capture field of a 6mx long yagi is likely to have far more effect on antenna performance than a fraction of a db of feedline loss.
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Re: Choice of cables for serious antenna systems

Postby vk3six » Sun Dec 27, 2009 12:22 pm

My trailer loaded with LDF4, cut all the brass N types off and sold them rest consigned to local scrap metal yard.
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Re: Choice of cables for serious antenna systems

Postby VK4WDM » Sun Dec 27, 2009 8:37 pm

This old bloke is getting confused with all the advice (goes with the age) :? :? :? and I don't have Steve's professional knowledge to sort it all out. My new setup will be as follows:

I will have 6m, 2m, and 70cm yagis fed by a single feed line with multiplexers at each end.

The total run will be about 35m but line needs to be flexible as there are some corners to go round.

In plain terms, what should I use for the feed line?

73

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Re: Choice of cables for serious antenna systems

Postby VK2SWL2 » Sun Dec 27, 2009 9:50 pm

At the risk of getting my head bitten off as I'm not an amateur operator, I will approach this from my job as a microwave network engineer. We work with unlicenced products at 900 MHz, 2.4, 5.4 & 5.8 GHz (as well as licenced microwave, but in that case the radio goes directly on to the back of the antenna so feedline loss isn't really an issue).

I will admit that our job is a little different, we have a known distance to the far end station we are trying to connect to, as well as known transmit powers and receive sensitivities. So we can easily plan a link budget and determine what size antennas are needed and what loss we can tolerate in the cable run. So in 95% of cases we aren't trying to squeeze every last fraction of a dB out of the link.

Cable specifications are fairly easy to come by online, so it is easy to calculate the loss you will have running LMR400 vs LDF4-50 (or whatever) for the cable run up your mast. I would suggest at 50 MHz the differences would be minimal unless it is a seriously long run. Then you need to take into account the flexibility required at each end - can you run the LDF4-50 directly into your antenna or will you need to terminate it and run an LMR400 flylead to the antenna. The same at the bottom in the shack, where LMR is definitely preferable so the stiffness of the cable isn't putting strain on the connector at the back of the radio.

We have always been told that a termination can introduce 0.2-0.5dB of loss sinply due to the different spacings as opposed to the coax run (and of course the quality of your termination). So by having to reterminate and introduce a flylead you could be introducing up to 1dB of loss, though this may be less at 50 MHz opposed to 2.4 GHz. But balance that against the difference in cable loss for your run.

The other thing is that LDF4-50 is a pain to run if you have to haul it around corners and so on. It's just too stiff to easily pull. It can kink if you try to pull it around a corner too hard which will damage it's performance. Sure, if you go straight out of the shack and up the mast it's fine. If it is a more complicated cable run then getting it where you want can be a serious effort - compared to LMR400 which is reasonably flexible.

It's really a case of horses for courses. Calculate the loss difference between the 2 cables, and any terminations you might have to make. Even if LDF4-50 comes out marginally ahead with those then you need to balance the ability to pull it through your cable run to where it needs to get to. Of course resistance to bird attacks etc may also be an issue depending on where you live, in which case flexible conduit may be advisable if using an LMR400 run.

The most important thing we have found for long term success is waterproofing. Get some good quality self amalgamating tape which if you aren't near a ham radio shop is available from electrical wholesalers like JR Turk or TLE (or their equivalents in other states). Seal any connectors really well, and then wrap in normal insulation tape as the self amalgamating isn't that UV resistant.
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Re: Choice of cables for serious antenna systems

Postby VK2AAH » Mon Dec 28, 2009 7:29 am

50MHz is not microwave. If I found a flylead with 1db of loss I would be taking a close look at the lead- it just shouldn't happen.

Unfortunately I think this discussion has drifted away from the original advice sought by Steve. From what I could see he is after a cable that is robust, long lasting, relatively rigid, and relatively low loss. Every cable has its pros and cons and it always comes down to the purpose in selecting the best for the job.
The merits of each have now been flogged to death, but I should make one last point- if I was rerigging a tower I would place robustness & lifespan of the cable ahead of a db or two. You can always recover a db or two through the antenna, but having to replace feeders every few years is a pain & an expense most don't want to have to go through. Good quality, properly fitted, and properly waterproofed connectors come in to that- I am constantly amazed by people who should know how to terminate a connector properly, but can't. It is always satisfying to recover a feeder after 10 or more years in service to find the connectors as good as the day they were fitted.

I still question the mentality of some microwave types with their fixation on dbs. Surely if a link is designed with a proper fade margin losing a db or two should not be an issue? Is it because some people don't know how to design links properly? But I digress...

Regards,

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Re: Choice of cables for serious antenna systems

Postby VK2SWL2 » Mon Dec 28, 2009 8:48 am

True enough Richard, which is why I mentioned that 95% of the time we aren't trying to scrape every last dB out of a link. I guess the obsession with dB is because we are designing the link properly, plus doing the calculations that show what we should get in theory are a nice backup to knowing it is installed correctly when we get that result after we put it up.

The discussion had also drifted away from 50 MHz a bit, to include at least 2m and 70cm - but of course the theory raised is valid for any other band you choose to think of. And I agree, robustness of the cables and connectors is very important, a lot of our antennas might be at the top of a 15 metre telescopic mast requiring a cherry picker or dropping the mast to perform any maintenance. I would rather put it up right the first time.

And like you say, I have come across plenty of poorly waterproofed and bad connectors out in the field, generally on links installed by other companies who are no longer in the game and we have taken over the maintenance for that customer. We shake our heads at some of the installs we see!
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Re: Choice of cables for serious antenna systems

Postby vk3six » Mon Dec 28, 2009 1:41 pm

I am constantly amazed by people who should know how to terminate a connector properly, but can't. It is always satisfying to recover a feeder after 10 or more years in service to find the connectors as good as the day they were fitted.


Thanks Richard.

I stripped the feedlines and have gone through each one.
The LDF-4 that I had on the tribander has 0.4db loss at 50 megs so its going into that role.
The RG10FB runs were 0.5 db and 1.8db
Pulled the 8db one apart and reterminated the connector correctly.
Trimmed it back removed the foam damage as per VK5PJ's suggestions water only ingressed afew mm.
Both the sheaths of the RG10FB are fine as I used fly leads and the main cable was surroundd by other cable.
The 9913 on the 2M vertical is stuffed.
I hated that cable anyway due to how fragile it is and how thick the centre conductor is to solder to a Type N.

My RG50/Foam 99?? is also a bit frazzled.

So I have enough to feed the three antenna up top.


I am not fussed by the interaction between the HF array and the 6M beam choosing instead to balance my operating
and not be 6M-centric to the extent that when the band is shut you cant migrate somewhere else.
Also 10m is essential for monitoring rising MUF through the 28 beacons into the 39 meg and 40 meg sub TV bands to track any out of band stuff.

My Band 1 TV antenna is going back up under the 2M pole as too many errors are occuring in D'Fing the 55.250 TV.
In a seperate topic you will see antenna reverses at 55 MHz.
I am hearing TV from over the pole like in 1998 and I would like to explore and if possible exploit that path,
it is after all the shortest way to CE/LU/and ZS from here.
Just climbing up and down and terminating and unterminating the cables for the last check before sealing nup for another 10 years.
cables all went up in 1989 and a revamp in 1999.
I will be too old and creaky to climb in 2019.
Too many hams have been injured climbing anyway and my tower is out of reach of a cherry picker.

cheers see you around 6M.

With the new LDF4 tracked E51 beacon for over 2 hours today.




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Re: Choice of cables for serious antenna systems

Postby VK2XSO » Wed Dec 30, 2009 6:33 pm

I'll keep an eye out for you Matt,
We chuck out whole lengths of various kinds of heliax, 4-50, 5-50 and the various RFS equivalents as well as LDF1/2-50/75.
I usually just cut the 4-50 connectors for my local club. I just chuck them in a bucket and ever couple of club meets I pour them out on the floor and they pick up what they need.

I'm curious to know if any other hams use DIN connectors ?
They're rather big and clumsy (and expensive) by ham standards, but their performance is very good and there is so many of them
surplus. Hams show no interest in them, so I don't bother recycling them other than for myself.
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Re: Choice of cables for serious antenna systems

Postby VK3ALB » Tue Jan 12, 2010 8:58 am

Matt it seems strange that you would find a significant difference between the two. What is your feed line length and can you quantify "way down".
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