Why good antennas need to be fed with good coax

Dennis Walter, of Bonito Radio in Germany, has just posted an excellent article on his blog regarding the importance of quality coaxial cable to fight local radio interference.

Click here to read his post, “Why even good antennas need good Coax cable.”

 

8 thoughts on “Why good antennas need to be fed with good coax

  1. DL4NO

    A very valid point. See my comment on the Bonito blog.

    Short form: For pure receiving systems simply use 75 Ohms TV SAT cable: Equally well shielded and mich cheaper.

    Reply
    1. DanH

      RG-6U quad shield is a middle quality 75 ohm coaxial cable but it works fine for me for SWLing purposes. It’s available at Home Depot in various lengths. It is a bit thick, stiff and cumbersome to work with but it is well-shielded.

      Reply
      1. DL4NO

        There is only one way to decide:

        * Install your cable.

        * Terminate the antenna end with an terminating resistor. If you cannot get one solder a 68 Ohms resistor between center coductor and shield.

        * Connect the other end to your receiver.

        * If you still hear to much noise: Get a better shielded cable.

        Reply
        1. Guy Atkins

          This is basically what I like to do, but I have a 75 ohms termination fitting (from CATV suppliers) that I use with RG-6QS Quad Shield when I replace coax. The terminator is this style: http://www.ebay.com/itm/BNC-terminator-cap-75-ohm-male-connector-plug-cover-adapter-TV-cable-RG6-RG59-/380947401562

          As Dan says, Home Depot is a great source and the cost is reasonable for quad shielded cable.

          More recently I found a large spool of Belden 7916A at an attractive price; this 75 ohm coax has a quad shield which Belden calls “Duo-Foil”. It seems to have better shielding than the Home Depot cable.

          Reply
    2. Tom Servo

      I tried TV cable that was left over from our satellite installation, and it was so noisy compared to “standard” coax I thought there was a break in the insulation somewhere. It just let in tons of local noise from the PC and other electronics in the shack.

      Reply
      1. DanH

        My experience with RG6/U Quad Shield listening to HF and VHF up to 54 MHz has been very good. I have an external 106′ random/long wire antenna. This antenna is 18-guage wire and includes an additional 15′ of wire running from the garage end of the antenna to a garage work bench where I listen to my radios. Last fall I added another 75′ feet of wire as a lead-in into to the house because it was getting too cold to enjoy listening in the garage anymore. I also had a Hammarlund SP-600 out there that I refurbished last summer. I didn’t want that out in the humidity over the winter.

        The additional 75′ length of wire added a lot of noise to the bands without any gain in signal. Using a tried and true RFI detection method I set the whip antenna on the Sangean ATS-909X to about 2′ in length and started “sniffing” along the new wire run for noise. Sure enough, a considerable amount of noise was emanating from a remote controlled garage door opener. The wire passed within 4′ of this device. Another source of RFI was discovered coming from an automatic sprinkler control box and its wall wart power supply located on the wall between the garage and the house. I could receive both sources of RFI inside the house at the listening location in the den. Also, noise from one CFL that I happened to leave powered up in another room and my computer monitor was much stronger in the den than it was out in the garage.

        Replacing that additional 75′ of lead-in wire with RG6/U Quad Shield eliminated all RFI coming from the garage and significantly reduced the CFL noise. The noise from the computer flat screen was greatly reduced but not eliminated. But, this monitor is located only a few feet away from my radios. I learned earlier to use my smart phone instead of the desktop if I needed to go online while SWLing. I have noticed no issues with that. No problems with the WIFI box either. That device is also located in the den. I’m happy with this set up for now. Reception in my den is every bit as good now as my garage listening post and a lot more comfortable.

        Reply
        1. DL4NO

          You were lucky that you could locate the RFI sources. Quite often the RFI is wirebound and cannot be located. Most often it is radiated from the mains wiring. PLC systems are one example. I had quite some search to do to find an USB power supply.

          As I mentioned it is good practice to add some form of curent yoke near the ends of the cable. Perhaps this is a way to reduce the flatsceeen noise.

          Reply
  2. Mario

    And what’s nice about using 75 Ohm satellite cable is no soldering’s needed; a set of compression/crimp tools and waterproof connectors make it so easy to cut to convenient lengths.

    Reply

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