Using cheap RG-6 coax as feedline for HF Ham Radio

Discussion in 'Tips and Tricks' started by K7JOE, Jun 28, 2021.

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  1. K7JOE

    K7JOE Subscriber QRZ Page

    Don't throw that old cable TV coax away. Put it to use as ham feedline. It's a solid copper or copper coated steel center along with double shielding using aluminum foil and braided aluminum. I have had very good luck using low cost, widely available RG6 "dish / direct tv" satellite TV coax on the HF ham bands for simple, low cost, effective HF antenna feedline.

    With just a few tips, this coax can be inexpensive alternative approach to high dollar coax cable feedline to get a budget minded ham on the air.

    First of all, despite what some experts may say, RG6 coax of all varieties can be used effectively as HF radio feedline. I've used and tested this stuff from 160-6 meters and up to 1KW output power with no bad effects, no blown radios, no broken amplifiers etc. It works. It's widely available even in most big box hardware stores, and it's inexpensive. Several times over the past few years, I've bought brand new unused rolls of coax, ie a 500 ft roll for $20, from our Habitat Recycle store. It's everywhere and that's what makes it cheap. Loss is negligible at the HF frequencies...and it probably can work fine even up to 2M !!!!

    Is it 50 ohms ? NO. This is 75 ohm coax. But guess what. A dipole feed point is 72 ohms so it is actually ideal for HF dipole use.

    Does it matter that it's not 50 ohms? And.. Will I blow my radio finals ? What are solutions?

    If you are using an older radio with tube finals, like the Kenwood 520 or Yaesu 101, just build the antenna to spec and then use the built in load control to tune up the antenna. Worst case you will see a 1.5 VSWR but you can use the pi network output just like an antenna tuner and you'll make lots of QSO's.

    If you are using a modern solid state radio, don't despair. You won't have a 1:1 match but we seldom realize that even on 50 ohm coax in the real world. This coax on a resonant antenna should have an SWR of around 1.5:1 ... which is perfectly acceptable. If your rig has a built in antenna tuner, just push the tune button and it should work great.

    If you're really concerned, select the frequency/band and cut the feedline length to the 1/2 wavelength length for the feedline or a multiple of the half wavelength (on 40 meters, it should be 65 feet...or 130 feet...or 195 feet and so forth). This is a special length that allows the impedance to be the exact same as it is at the antenna. A real simple solution if you're "worried".. and due to the cheap price, a few extra feet or yards of coax wont hurt a thing.

    For simple dipoles and other simple antennas, this stuff works just fine.

    Can I use PL259 connectors with this coax? Isn't the shield Aluminum ? What to do?

    You can not easily - directly use a solder on PL259 although some guys have done it successfully, usually the UG176 reducers fit RG8X and RG59 coax...but not RG6. Plus, even a silver PL259 won't solder to the aluminum jacket / shield. So what to do? I like to use this method. I install a now insustry-common l compression fit male screw on "F" connector on the coax end. These are high quality and can be water proofed easily. Then I use the cheap $2 adapter to convert from female F to male PL259 . Amazon is your friend here. You can get the compression tool and a dozen F connectors for around $10 bucks. Still loads cheaper than the $100 roll of RG8 coax from hamradiosupplycompanyoutletengineeringelectronics.

    How do I connect aluminum to copper wire ?

    Connecting the "business end" of the coax up to the two wires of a dipole is easy to. I use a direct connect method (no incremental connectors). I usually solder the copper center to the copper wire. But the aluminum shield can't really take solder without a lot of heat. So, most of the time I use a crimp for the aluminum shield (to connect both ends to a wire dipole). Crimping is the method recommended and has been used for aluminum to copper wiring for decades. You can buy the copper electrical crimps and they work great....I picked up 100 in a bag for around $20. You can buy 5 or $1 if you just need a few connections. Remove the foil inner shield, you'll be using the aluminum outer shield. If you want to solder the copper to the aluminum, I have found that heating the aluminum a lot with a torch, it will take some solder with a little bit of tinning flux. But again, crimping works and is simple and will last and last. Tip: check continuity any time you install F-connectors. Make sure there are no shorts.

    At field day this year, I demonstrated putting together a $20 antenna (including feedline - everything needed to get on the air) using a hunk of RG6 coax with a simple 40/15 dipole (two money-bands for field day). The antenna worked great. First Q when testing was with Spain (from Indiana) in the daylight hours on 40M with 100W. I think they worked 1000 QSO's on that antenna. It was up around 35 feet. Inverted Vee config. The RG6 and dipole tune up was a snap. The "curve" was 2:1 VSWR across the entire 300 khz of the 40 meter band and the lowest point was 1.2:1 .... perfect !

    End insulators, antenna wire, center insulator, a few zip ties, 200 ft of RG6 coax, an electric crimp, an F compression connector and an F to PL259 adapter. The whole enchilada for less than a $20 bill. Best of all, several new hams learned how to save a few bucks using what we have right at our fingertips to get on the air and make some HF noise.

    Give it a shot. You might be surprised how this inexpensive coax compares to your high-dollar 50-ohm coax cable solution. Especially ideal for temporary / portable installations like field day or one-off experiments where you don't want to have to spend big $ on an extra feedline.

    PS. I did not test this coax fully at VHF or UHF, but no reason to think it wont work for 2M and probably 220 and 440 too. The spec is actually quite good at these frequencies. It was designed for satellite use, which is even higher frequency.

    PSS. In the old days, some white-jacket RG59 and later RG6 coax was designed for indoor use Now days, most of the RG6 coax that I've found, even the white jacket stuff, now is acceptable for indoor-outdoor use. The cable has some numbers on it and you can look up the spec of the stuff you have online. It's cheap... So you can experiment and see what you find.
    WB2JAX, KK4NSF, W7JMP and 10 others like this.
  2. WN2SQC

    WN2SQC XML Subscriber QRZ Page

    Excellent idea and description, thanks. I’ve used the same coax for all my ham feed lines. Sold all my other coax. I bought a 1000 foot roll on ebay delivered For $42. So much easier to use.
  3. KX4OM

    KX4OM Ham Member QRZ Page

    For single-band use, the 75 to 50 ohm mismatch, little that it is, can be addressed at the shack entry can be using a 12th-wave transformer section. It's in the ARRL Handbook, and it involves a short piece each in series (12th wavelength each, factoring in the velocity factors) of 50 ohm and 75 ohm cable. The loss due to additional connectors is negligible. The end result is 50 ohm coax to your rig or antenna tuner. I use RG-8X and RG-59 for the 12th-wave transformer section, since UG176 adapters will fit both.

    Ted, KX4OM
    KM1H and K7JOE like this.

    GNUUSER QRZ Member

    75 ohm cable can be used as a feed line without a matching transformer IF your antenna system is co-phased for example a co-phased delta loop would use a 75 ohm cable as feed line
    K0UO likes this.
  5. K7JEM

    K7JEM Ham Member QRZ Page

    One comment I would make is that the half wave coaxial length will have to be calculated using the velocity factor of the specific coax. So, it will actually be shorter than 65 or 130 feet or whatever.
    W9JEF likes this.
  6. N1IPU

    N1IPU Ham Member QRZ Page

    I have a 1k roll of outdoor buried rg-6. It's the trick item is you experiment with antennas. Most of the time experimenting is held back by costs so it makes sense to use this stuff that can be had less than nothing if you know where to look.
    I use F connectors to keep it simple most often then adapt at the shack.

    Great post OP.
    KK4NSF, K7JOE and (deleted member) like this.
  7. K7JOE

    K7JOE Subscriber QRZ Page

    yes, this is true, in all cases.

    The length suggested for a 1/2 wave matching section has to consider the coax VF. I believe this stuff I found (500 ft roll for $19) is VF= 0.91 as I recall...

    But again, the mismatch is actually pretty negligible at HF frequencies and probably makes no noticeable impact and today's built in automatic ATU, or a manual or automatic external antenna tuner easily solves any mismatch issue.
    Last edited: Jun 29, 2021
  8. K8JD

    K8JD Ham Member QRZ Page

    I have used 75 Ohm cable-TV drop cable "Q sections" to transform some ~150 Ohm feed antennas (like a single band FW loop, or an EDZ) to a regular 50 Ohm feedline. I still like RG8-X coax for the main feedlines.
    WB2JAX likes this.
  9. W0RIO

    W0RIO Ham Member QRZ Page

    I purchased about 200 feet of something close to RG-6 at our local recycled building supply outlet for $5 and
    have used it for quite a few antenna feedlines. It's not the typical RG-6 though, it has a solid copper center
    conductor and dual copper braids for the shield. It solders nicely into a PL259 using a UG176 RG-59 adapter
    if you remove the outer plastic where it enters the adapter.

    I also bought a large spool of all-copper RG-58 coax for a few bucks at the same store and have used that
    for the elements of numerous dipoles and top-hung vertical antennas. Connections are done with either solder
    or via a PL259 plug and socket. I use silicone to seal off anything that is exposed to weather.
    RG-58 works fine as an antenna element, it's a bit heavier than stranded THHN copper wire but it lasts
    a long time and holds up well under sunlight.

    I've also used the half wave multiple trick for feedlines, accounting for velocity factor. It's pretty easy
    to tune the length of the feedline using an MFJ-259 antenna analyzer, just short the far end and read the frequency
    where the impedance drops to minimum, then trim. Keep in mind that extra coax jumpers will lower the
    feedline resonant frequency. Resonant length feedlines aren't really necessary with properly resonated antennas,
    but they can help you get a better idea of what's going on at the antenna feedpoint.
  10. KP4SX

    KP4SX Premium Subscriber QRZ Page

    That may be CATV Headend Cable.

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