Author Topic: best practices for making coax patch cables?  (Read 12062 times)

Offline Smurf Hunter

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best practices for making coax patch cables?
« on: May 21, 2014, 05:43:20 PM »
so now that I'm "legal" and have all the gear to start transmitting, the next logical step is to begin messing around with homebrew antennas.

I'm seeing a ton of conflicting information about what style of coax and connectors to use.

e.g. this old timer demonstrates how to use RG-6 (which I believe is the cable TV type) and wraps duct tape to increase the thickness for the connector sleeve:
https://www.youtube.com/watch?v=tg2lmDETJTs

After I decide on what sort of cable is "good enough", what about the end pieces?

eBay has all sorts of bulk packs that ship for just over $1 each.  That seems reasonable for the small quantity I'll need, but are they "good enough"?
http://www.ebay.com/itm/NEW-20-pack-lot-UHF-PL-259-male-solder-on-RF-connector-plugs-for-RG8-coax-cable/271321083620?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222003%26algo%3DSIC.FIT%26ao%3D1%26asc%3D22854%26meid%3D7065634343819981048%26pid%3D100005%26prg%3D9833%26rk%3D2%26rkt%3D6%26sd%3D350958835907&rt=nc

In summary:

What are considerations when choosing coax?

What are considerations when choosing PL-259 end pieces?

Offline Chemsoldier

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Re: best practices for making coax patch cables?
« Reply #1 on: May 21, 2014, 06:30:38 PM »
  :popcorn:

Offline Carl

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Re: best practices for making coax patch cables?
« Reply #2 on: May 21, 2014, 07:05:05 PM »
For my use ,RG8X and PROPER PL-259 connectors and INSERTS.
The RG8X has lower loss than many RG8 (thicker) coax cables and
I have had some in the air for over 25 years with NO problems.

Here is where I get coax,by the foot and PRE--MADE  lengths
from 2 feet to 125 feet . Many videos show how to solder coax
and look at a few to get ideas. Use proper inserts to adapt coax to
the PL259 to protect your work and the strength of the cable.


Cable by the foot
http://www.randl.com/shop/catalog/index.php?cPath=11020

Pre made, the Jetstream series is my favorite
http://www.randl.com/shop/catalog/index.php?cPath=11030

Also good weather-proofing is a MUST ,water and moisture will degrade cable quickly.
Self vulcanizing tape ,usually silicon,with a friction tape  over wrap to protect from UV works well.
Also limit free hanging ( tape to support every 5 to 10 feet) and sharp bends and CRUSH should be avoided.

Just my thoughts , and suggested cable.
The pre-made lengths are so close to component cost,I just buy ,unless in a rush.

When making a cable,ohm test for complete , center to center-shield to shield connection and
center to shield should always measure as OPEN...infinite resiatance.

Offline TexasGirl

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Re: best practices for making coax patch cables?
« Reply #3 on: May 21, 2014, 11:27:21 PM »
RG 59, RG 6, are "TV" type cables with a 75 ohm impedance.  They are rarely used in 2-way radio equipment because our gear is designed for 50 ohm antenna systems.  (Yes, a center fed dipole is technically 75 ohm, but your rig wants to see 50.  That's what baluns are for.)  Don't use these cables for ham use outside of ATV.

RG 58, RG 8, RG 8X (sometimes called "mini 8"), RG 142, and Heliax hard line are commonly used 50/52 ohm coax cables.  You will learn which ones to love or hate under which circumstances.


TG's ramblings for consideration...

I prefer soldered connections over crimped, moisture or corrosion can get in a crimp.  Solid Polyethylene dielectric repels moisture better than foam dielectric, so solid dielectric makes better outdoor cables.  RG 142 is very flexible, commonly used as jumpers for test equipment.  RG 8X is only slightly larger than RG 58, but has lower loss and higher power handling similar to RG 8.  Because it has foam dielectric, it's not best for permanent outdoor installation, but is hard to beat for a field deployable rig.  (Use RG 59 reducer barrels in PL 259's with RG 8X cable.)  Adapters are great in a quick fix, but they can cause trouble over time in permanent installations, every additional connection has some sort of loss or imbalance.  Use correct cables where possible.  Cable loss is more important at higher frequencies (2 M, 220 MHz, 440 MHz).
 
Good antenna projects to begin with are longwire dipoles and J-poles.  The ARRL Antenna Handbook is great to have around.

Happy Soldering!

~TG

Offline Carl

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Re: best practices for making coax patch cables?
« Reply #4 on: May 22, 2014, 04:49:03 AM »
Not to sound argumentative , but to ramble on the subject.

But ,in my understanding:
Foam core is not an issue with moisture (though a foam outer jacket would be) A properly sealed PL-259 will not let water into the core and FOAM has a more consistent dielectric and RF characteristics,it is MORE STABLE  (that's why Mini_8 is better and lower loss) though 100 feet of Mini 8 still loses almost HALF of your VHF power.

The great jacket,heavy shielding and thicker stranded core all lend to the above average RF characteristics and below  average COST of the MINI 8. It is NOT the best,but it is the best balance of function and economy. In my opinion.

And on to 70 ohm coax, your radio expects a 50 ohm load,and 50 ohm coax is a good choice.

BUT a dipole is accepted as 72 ohms ,or so,impedance .( go figure that one out) and verticals often are 31 to ? ohms.

In actuality the trouble with  other than 50 ohm feed line is finding the connectors to mate it to 'our' devices.
Noting that HARD LINE is the often described  BEST for HAM use ,though most hard line is 70 to 90 ohm impedance.
and let's not even go to the fact that 300 and 450 ohm ladder line are the lowest loss choice for many antenna applications.

Please don't think this a critical view of you or your thoughts on feed line, it is not.In fact,re-reading, we are much in agreement. Though you gotta' tell me how the core material is responsible for keeping water out, I always thought it was the outer jacket. Once water gets past the outer jacket,RF characteristics and your signal really suffer. But often ,due to
high loss, a corroded shield reads acceptable SWR while performance of the antenna suffers.

When ,and why,did SWR become the yardstick to judge antenna effectiveness or even "TUNE"??
As once cut to length,any trimming will only diminish antenna efficiency ,though it may make the radio happier,or the operator.

TG and others , I am interested in your thoughts on this often argued subject
TG??? wow ,you really are well versed in some heavy stuff. we have close to
the same opinion,viewed from different angles.

All of my feed line is 50 ohm,except for 300 ladder line on the G5RV.

Boy,did I ramble, maybe the MEDs I take are needing adjustment.

Offline TexasGirl

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Re: best practices for making coax patch cables?
« Reply #5 on: May 22, 2014, 09:39:41 AM »
Hey Carl,

Well....  You certainly have me beat on rambling.   Can't relate on the med subject though, I have a no-med philosophy.

I wasn't trying to get too deep into RF and hardware philosophy, or make these new ham's heads spin, but I will attempt to answer your questions.

Basically, vinyl jacket and foam are great for flexibility but not weather durability.  Vinyl microscopically pinholes over time (especially with UV exposure) allowing moisture to infiltrate the braid and dielectric.  There's a reason outside plant telephone cables are made with polyethylene (PE, HDPE,) and polypropylene, not vinyl.  So, it would have been better for me to have said use polyethylene jacket and dielectric outside.  Technically, a vacuum is the best dielectric, followed by air, foam, teflon, then PE.  Each cable is a compromise of properties needed for a particular purpose.  Foam dielectric works in hardline because the shield is basically solid copper tubing. 

Coax breaks down electronically in two ways.  As moisture begins to corrode a braided shield (or in a connector) it's capacitive properties change and become reactive.  Each place two corroded conductors cross becomes a reasonant point (how many points are in braid shield?)  This will cause an imbalance in SWR or simply a place to facilitate intermodulation.  Moisture in the dielectric changes the velocity of propagation, effecting the efficiency, and can even allow a hi impedance short between center conductor and shield.  Much like static on a phone line after a rain on bad spot of cable.

30 ohm coax inherently handles more power, 77 ohm is the lowest loss.  That's why CATV systems use 75 ohm, they are running long distances.  The RF industry chose 50 ohm as a compromise between power and low loss. 

Antenna impedance changes with its environment, especially its relation to ground.  Take that halfwave dipole with a free space impedance of 75 ohms, as it approaches the ground it's impedance will drop.  The same 1/4 wave radiating element, vertically at ground, or with radials making a ground plane, will be close to 50 ohms.  The two-way industry revolves (or evolved) around that magic 50 ohm match.

Remember, braided shield on cables leaks, it is not solid, but is generally made to a 91% or 88% standard, although some cheap cables can be as poor as 60% shield.  Sure, it appears more or less solid to many RF frequencies, much like a faraday screen cage, but it still leaks.  For permanent cables, I like dual braid where flexibility is needed, and "quad shield" (which is a foil under braid construction) where flexing will not break down the foil over time.  Why worry about braid leak?  One of the most overlooked hazards is leaky RF radiation.  It's good to check your ham shack periodically with a "S" meter to see how much RF is inside the shack when gear is keyed at various frequencies.

~TG

Offline Smurf Hunter

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Re: best practices for making coax patch cables?
« Reply #6 on: May 22, 2014, 09:59:27 AM »
Lots more brain dumping for me to digest...

Some more tactical questions.

What is the best balance of performance and economy for the following uses:

1) cable running outside my house up to a roof mounted antenna.  I live in the Seattle area, and we get rain, some wind and occasional sub-zero temps in the winter
2) cable inside the HAM shack used as short length patch cables
3) cable buried underground
4) cable run inside walls of a house

Is it reasonable to buy a single big spool of coax that meets all these needs well?

Offline TexasGirl

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Re: best practices for making coax patch cables?
« Reply #7 on: May 22, 2014, 10:30:36 AM »
Lots more brain dumping for me to digest...

Some more tactical questions.

What is the best balance of performance and economy for the following uses:

1) cable running outside my house up to a roof mounted antenna.  I live in the Seattle area, and we get rain, some wind and occasional sub-zero temps in the winter
2) cable inside the HAM shack used as short length patch cables
3) cable buried underground
4) cable run inside walls of a house

Is it reasonable to buy a single big spool of coax that meets all these needs well?

LMR 400 UHF, and LMR 600 UHF, are kind of the industry standard for outdoor use.  If you are planning to be there awhile, and you can afford quality, Andrew is the Mercedes of cables.  I'd consider getting a roll of either their Cinta CNT-400 or CNT-600.  400 flexes better, 600 is better in rigid environments.  For patch cables in your shack, any double shield cable will work fine.

~TG

Offline Carl

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Re: best practices for making coax patch cables?
« Reply #8 on: May 22, 2014, 03:47:47 PM »
I have to agree with TG on LMR,just a bit out of my budget...But do it RIGHT and SEAL the connections and you will not have to do it again. Mini 8 is a budget helper,if the COO agrees with the cost ,go for it . Though it is good ,sub zero will cause degradation in mini 8..I just do not know how much as even 25 degrees is rarely seen here in Louisiana.

Offline Smurf Hunter

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Re: best practices for making coax patch cables?
« Reply #9 on: May 22, 2014, 04:02:09 PM »
My area probably has about 6 weeks where it drops below freezing at night, but thaws during daylight hours.  Nothing near as cold as northern midwest states.  It's quite rare that the temp remains below 32F for more than a few days.  (this is actually rather annoying as each morning there's a fresh sheet of ice on the steep roads).

If I were to permanently mount an antenna on my 2nd story roof line, and fish the cable down the side of the house, and into the HAM shack, etc. it might be worth the investment of premium cables.  Climbing ladders is not my favorite past time and I just assume do it right once :)

That said, as I'm experimenting with DIY antenna designs at a picnic table, I certainly don't need the best cables.

Thanks for all the knowledge transfer folks!

Offline backwoods_engineer

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Re: best practices for making coax patch cables?
« Reply #10 on: May 23, 2014, 12:23:12 PM »
Years ago, at a surplus sale, I came into a good deal on a nice long roll of Belden 9913F, a 50-ohm coax that is a lot like LMR-400 loss-wise, the same diameter as RG-8X, but more flexible.

That has lasted me until now.  I make all my ham radio cables from HF to UHF out of that.

I always use either crimp or solder silver-plated PL-259's or N male connectors.  I am leaning toward all crimp now, because they seem to weather better (crimp connections as gas-tight).


Offline armymars

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Re: best practices for making coax patch cables?
« Reply #11 on: March 05, 2015, 04:19:32 PM »
  Good cable is important for other reasons. I have bought cheep RG8X to make jumpers. The problem was the center conductor would break if flexed too much. Look Ma no conductivity. The old foam centers found in co-ax was open cell foam so any moister would follow along the length of it. That was before we had "Coax Seal" and other products to take care of it. If you didn't use these products to seal the ends (just tape) it would not be long before you had trouble.
  9913 has other problems if not sealed with a gas type seal. As the atmospheric pressure changes it would drive air in and out of the co-ax which is mostly empty. If wet air went in then it would leave the water behind when it came out. The engineers have a name for this, but I can't remember it. I once built a 2 meter beam and sealed the brazing rod elements thru the PVC boom with a glue gun. work great for two week then wouldn't take power. I pulled out an element and pored a 1/4 cup of water out of it. No joke. No rain during the two weeks. Surprise!
  In Europe hams like to use 75 ohm co-ax to match the antennas then a tuner to the radio. More later diners on the table.

Offline PrepperJim

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Re: best practices for making coax patch cables?
« Reply #12 on: March 28, 2016, 12:48:16 PM »
Thanks for this thread. I had exactly the same questions as Smurf....two years later.

Offline scoob

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Re: best practices for making coax patch cables?
« Reply #13 on: March 28, 2016, 09:35:40 PM »
Quote
In Europe hams like to use 75 ohm co-ax to match the antennas then a tuner to the radio. More later diners on the table.

Interested in the follow up on 75ohm.  I inherited a spool of catv coax, and was wondering if it's worth using as hf or vhf feedline, or is it scrap?  (I'm not in Europe though)

Also, on the OT... patch cables between tuner/radio/meters/etc.:  are there special considerations for building cables with such a tight bend, or minimum cable lengths between devices that should be maintained?

Offline Smurf Hunter

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Re: best practices for making coax patch cables?
« Reply #14 on: March 28, 2016, 11:15:50 PM »
Interested in the follow up on 75ohm.  I inherited a spool of catv coax, and was wondering if it's worth using as hf or vhf feedline, or is it scrap?  (I'm not in Europe though)

Also, on the OT... patch cables between tuner/radio/meters/etc.:  are there special considerations for building cables with such a tight bend, or minimum cable lengths between devices that should be maintained?

Personally I think rg8x is the best all rounder.  It's thin and easy to bend, and unless you have a considerable distance is tolerable loss on VHF, and I just accept the loss for the little UHF work I do.

Offline Carl

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Re: best practices for making coax patch cables?
« Reply #15 on: March 29, 2016, 06:39:12 AM »
I often use a 6 foot ,Mini 8 jumper as a way to allow movement and flexibility on my radio desk...a two foot cable prevents you from having a range of motion between radio/tuner/SWR meters/antenna switches and I find it pays to have a range of motion and organization of radio components. Losses are minimal as the length is nowhere near the 100 foot measure on the LOSS CHART.

I have found the RG8X to be far better than generic RG8 as SIZE of coax has little to do with quality or loss. I also have used 75 ohm coax many times as it is often of great quality and makes great matching harness for multi-antenna arrays and also helps with antenna mis-matches...a 75 ohm coax is well within the capability of a 50 ohm radio...

Why is it that Hams leap at the chance to use 75 ohm hardline??? While ignoring quality feedline...mating the coax to the PL259 (connectors) is the hardest part of using 75 ohm coax   and I have found adapters are not too tough to find as this has been done many times before.

I use 400 ohm ladder line as it is lower loss than the best coax and my radio likes it just fine with the addition of a balun...even when the balun does not provide the coveted 50 ohm match.

The antenna matcher (auto tuner) keeps the radio happy in most cases of mismatch and PROTECTS YOUR VALUABLE GEAR from most problems that feedline and antenna can generate.While the 'correct' item is often better,a thinking Ham can do many things that ,at first,appear to be 'against the rule' of antenna and feedline use. I ran a 2 meter antenna with a balun and two wire extension cord and have also used TV antennas for VHF (remember them?) Often you don't have the luxury of time and lives can depend on YOU.

Sorry to get off on a emergency rant...but my auto tuner allows most any antenna to work for me and my radio and we are preparing for what could be emergency comms....aren't we.
« Last Edit: March 29, 2016, 06:48:43 AM by Carl »

Offline Alan Georges

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Re: best practices for making coax patch cables?
« Reply #16 on: March 29, 2016, 06:58:49 AM »
  In Europe hams like to use 75 ohm co-ax to match the antennas then a tuner to the radio. More later diners on the table.
Well, it would give a better match at an ideal dipole's 73 ohm feed point.  Then you match the transceiver's 50 ohm output to the feed line at the shack with a tuner, and everything's pretty smooth at every step along the way.  I can see it. 

Probably not that big a deal either way for HF.  Maybe not worth the hassle, but if the coax is free, why not.  High up the bands, do you really want to use a tuner at VHF/UHF frequencies?

Offline Carl

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Re: best practices for making coax patch cables?
« Reply #17 on: March 29, 2016, 07:16:33 AM »
Well, it would give a better match at an ideal dipole's 73 ohm feed point.  Then you match the transceiver's 50 ohm output to the feed line at the shack with a tuner, and everything's pretty smooth at every step along the way.  I can see it. 

Probably not that big a deal either way for HF.  Maybe not worth the hassle, but if the coax is free, why not.  High up the bands, do you really want to use a tuner at VHF/UHF frequencies?

You can use a tuner on VHF/UHF and often the antenna match is performed by a coil or shunt to obtain a reasonable match as in "J" poles and any NON 1/4 wave antenna...this is often done with antenna design rather than innovation of the Ham operator. Many antennas are designed with a shunt (SHORT at DC) that 'matches the antenna' but as most VHF/UHF are still comercial made ,the Ham seldom gives it a thought.

A lossy antenna that works is so much better than a golden yagi that refuses to pass RF. I use what I have and continually read,learn.plan.work to improve what I have. This is why my single antenna station has been heard in many parts of Europe and set the ARRL world record DISTANCE OVER LAND for VHF and it is just a simple station with a possibly simpler operator.

I am KB5WMY and it isn't bragging ,if it's true..

Hams do magic with RF.....

Offline davidradio

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Re: best practices for making coax patch cables?
« Reply #18 on: March 24, 2018, 01:46:06 AM »
You can use a tuner on VHF/UHF and often the antenna match is performed by a coil or shunt to obtain a reasonable match as in "J" poles and any NON 1/4 wave antenna...this is often done with antenna design rather than innovation of the Ham operator. Many antennas are designed with a shunt (SHORT at DC) that 'matches the antenna' but as most VHF/UHF are still comercial made ,the Ham seldom gives it a thought.

A lossy antenna that works is so much better than a golden yagi that refuses to pass RF. I use what I have and continually read,learn.plan.work to improve what I have. This is why my single antenna station has been heard in many parts of Europe and set the ARRL world record DISTANCE OVER LAND for VHF and it is just a simple station with a possibly simpler operator.

I am KB5WMY and it isn't bragging ,if it's true..

Hams do magic with RF.....

This answer made 4 years ago but now it still helpful for me. Thank Carl link!

Offline Carl

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Re: best practices for making coax patch cables?
« Reply #19 on: March 24, 2018, 03:04:02 AM »
This answer made 4 years ago but now it still helpful for me. Thank Carl link!

WOW, I am even impressed with my old answer..their are many ways to do the right thing though worry about SWR on antenna systems (within acceptable range to make radio 'happy') is just folly as trimming an antenna that was cut to proper length just introduces LOSS into the system to produce the Hams desired LOW SWR that has only criteria for the radio and NOT ANTENNA CAPABILITY...any wire or conductor NEAR or over 1/4 wave will be effective...SWR ONLY EFFECTS POWER OUT WHEN SWR CAUSES THE RADIO TO LESSEN POWER OUT and the established cut lengths are the correct length (for single band antennas)...I  use RANDOM length
Though they are narrow specific lengths to provide I can run many/all HF bands with ONE ANTENNA and I use an ANTENNA MATCHER,often called tuner...though it only adjusts the antenna system (environment,feed line,antenna impedance to a level the radio expects and is safe on the radio ...remember ANY WIRE within reasonable length NEAR OR OVER 1/4 wave will put RF out effectively and SWR adjustment is NOT an improvement on signal out ,only radio out and safety.

  If you only run one band,a properly cut 1/4 wave per side does perform slightly better as it lends one more resonant component to the system and ,I think,aides in sensitivity and selectivity a small bit though at a cost to coax feed lines due to the number of antennas the typical Ham desires for the flexibility to manage propagation and conditions better (bands don't work consistently due to environment change and solar storms etc)

I have many collected articles and some of my own designs and observations for antennas and more  available on my Google drive,safe and secure ...you ,and any one with the link can read on line or download FREE ,as I found them . Take all you might want as I nor my site are forever ,though the data will be current long after I am gone. What small gift to any who may wish it.

https://drive.google.com/open?id=0B5ZIZLZV4AwIMFlYMTI5OTNlUTA