Coaxial cables with joints

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

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  1. N1YR

    N1YR Ham Member QRZ Page

    Loss at 10 MHz is much less than 1 dB per 100 feet. Maybe about 0.4 dB per 100 feet per one listing. At that rate, to lose 1 "S" unit (6 dB) would require a coax length of 1500 feet. Even adding connectors, losses at the low end of HF are not a major concern, as long as the connectors are kept dry as previously noted.

    But as frequency increases, cable loss begins to increase by a lot. At UHF, the become critical, and better cables are called for in longer length runs.
    K4AGO and ZL1MTO like this.
  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Negligible losses added by the connectors in either scenario.

    Here's an old QRZ thread discussing RF connector/adapter losses. W8JI makes a very good argument that losses have to be much less than 0.1dB or the heating at the connector would be substantial at higher power which really isn't the case. N3OX also posts a pretty good example with 23 old and tarnished connectors of various sorts connected in series and resulting in pretty low loss:
    NL7W, N2EY, K0UO and 1 other person like this.
  3. VK6ZGO

    VK6ZGO Ham Member QRZ Page

    Providing the manufacturers were all reputable, it shouldn't make any difference, if they are the same impedance.
    In fact, at 10 MHz, you could even mix 50 ohm & 75 ohm cables with only a small mismatch penalty.
    W0FS and ZL1MTO like this.
  4. WA9SVD

    WA9SVD Ham Member QRZ Page

    If you are talking about HF, the insertion loss is negligible (provided you use good connectors, PROPERLY installed. The "cheep" connectors can vary all over the place.:rolleyes:) If you get into VHF, or UHF and above, then insertion loss due to connectors becomes an issue. BNC and/or "N" connectors (the usual types used by amateurs) will have constant impedance, and cause the least insertion loss, which for BNC and "N" will have low insertion loss (a few tenths of a dB at most) through 23 cm. Your coax run will probably introduce MORE loss than the connectors.
  5. SM0AOM

    SM0AOM Ham Member QRZ Page

    The actual losses at 10 MHz are very small in properly assembled coax connectors of quality manufacture.

    It becomes very difficult to measure the insertion losses of a few coax joints using quality connectors on HF.

    However, some cheap connectors may be manufactured using bad materials or with loose tolerances. This may create intermittent connections and heating due to contact resistances.

    Generally speaking, when connector losses are specified, the maximum loss per splice is in the order of 0.05 dB.

    NL7W likes this.
  6. K4PIH

    K4PIH Ham Member QRZ Page

    Cheap connectors play a big role. I've seen the cheapo 90 degree connectors (ones with a spring inside) actually melt and fail. Cheap coax also has a big impact, even at HF and more so at the higher frequencies. Also using adaptors, say going from N type to UHF and the back to N, can cause loss.

    I've seen connector cross over several times in 100' run of coax. People would rather use and adaptor kit instead of doing it right the first time.
    Last edited: May 21, 2020 at 2:00 PM
    K0UO and WA1GXC like this.
  7. W2AAT

    W2AAT XML Subscriber QRZ Page

    Since we are talking about 90 degree connectors. Does RF mind 90 degree connectors or is this just an "old wives tale"?
  8. K1VSK

    K1VSK Ham Member QRZ Page

    Only if they go right
    W2AAT likes this.
  9. W1VT

    W1VT Ham Member QRZ Page

    Connectors do become an issue at 10GHz. I have seen measurable differences in insertion loss using quality SMA connectors at 10GHz. As well as changes in circuit performance as I swapped cables.
    I'd build my 10 GHz transverters in connectorized modules and swap cables as part of the final assembly process.

    A lot usually changes when you change the dimensions by three orders of magnitude!
    Three orders of magnitude is the difference between a paper airplane and a Boeing 747.
  10. WF7A

    WF7A Subscriber QRZ Page

    Agreed, but my thinking is that whenever you put something together, eliminate as many variables (and physical parts) as possible to make troubleshooting and the analysis of results easier.

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