Coaxial cables with joints

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by ZL1MTO, May 20, 2020.

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  1. ZL1MTO

    ZL1MTO XML Subscriber QRZ Page

    Just would like to ask if anybody ever had a chance to test the effects of joints on coax cables and extra loss of signal.

    Lets say I have 100 feet of RG-8 operating in 10 MHz. Lets say that the loss is 1 dB for 100 feet on this frequency. However, what if:

    1) I have 50 feet of the coax connected to a female-female joint then another 50 feet of the same coax.
    2) I have 50 feet of the coax connected to a 1:1 line isolator, then another 50 feet of the same coax.

    All connectors are PL-259 and a SO-239 female to female.

    How much extra loss I will have on the scenarios 1 and 2 described above ?

    I don't have the proper equipment to run some testing therefore hope someone had a chance, equipment and expertise.

  2. WF7A

    WF7A Subscriber QRZ Page

    If I understand correctly, you're asking how much insertion loss there is per connection? Assuming a good/proper fit, not much--maybe 0.6 dB per connector if I remember correctly so you'd have to insert a lot of connectors before you can hear a practical loss of signal.
    ZL1MTO likes this.
  3. K6CLS

    K6CLS Ham Member QRZ Page

    0.6dB sounds like a lot, I remember it is more like 0.1dB. But yes, it's a very small number, don't worry about a few connectors.
    K4AGO and ZL1MTO like this.
  4. KQ0J

    KQ0J XML Subscriber QRZ Page

    The F-F connector is direct so very little loss - you can look up the specs for loss on the manufacturer website.

    The line isolator - Which I have used as you stated , will have a wee bit more loss - assuming it is like a MFJ-915 where there is a length of coax inside ( 13 inches of RG-303 ) which
    makes your effective length 1 foot longer.

    Loss difference is so small you need not worry about it.
    WA9SVD and ZL1MTO like this.
  5. ZL1MTO

    ZL1MTO XML Subscriber QRZ Page

    Thanks a lot for the answers. Actually the question is more related to cutting the cable and joining it.....instead of having a 100 feet run of the wire from the antenna to the radio, I cut it in 2 or 3 or even 4 parts and then join them together again.....Would it make much difference in terms of losses ?
    Assuming the joints are properly done of course, with proper soldering and connectors.
  6. ZL1MTO

    ZL1MTO XML Subscriber QRZ Page

    Thanks a lot
  7. WZ7U

    WZ7U Ham Member QRZ Page

    Only issue I can see could come from water ingress, either at the coax to connector vector or the connector to connector vector. Nothing a little "best practices" can't address.
    K4AGO and ZL1MTO like this.
  8. K1VSK

    K1VSK Ham Member QRZ Page

    No. The insertion loss is negligible.

    Most people with big towers and lots of antennas typically use different flex cables to the tower, up the tower, split through switches, flexible coax around rotors, etc... not a problem if done properly.
    ZL1MTO likes this.
  9. WF7A

    WF7A Subscriber QRZ Page

    I think you're right--now I have to figure out why 0.6 sticks in my head. : P

    Another item worth remembering is not to mix and match coax cables from different manufacturers and impedance ratings--that's where you'll run into trouble.
    ZL1MTO likes this.
  10. ZL1MTO

    ZL1MTO XML Subscriber QRZ Page

    Agree...thanks !

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