Discussion in 'VHF/UHF - 50Mhz and Beyond' started by F4HZN, Sep 15, 2018.

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  1. F4HZN

    F4HZN Ham Member QRZ Page


    This spring, I bought a Diamond X700HNA in the USA and it worked extremely well until yesterday : suddenly, the SWR on 70cms shows 5 :1! No change on 2m where it reads around 1.1:1.
    I checked the cable and connectors, using another antenna, it was ok.

    I dismantled the stick and found absolutely no hint of what it can come from !
    I usually use 70W in FM on 2m, may it have caused a problem in the capacitors that are to be seen at the base of the antenna ?

    Thanks for your insight.

    73s de F4HZN Laurent / Lawrence.
    PS. I meant "high SWR" not "hign" but can't edit the title...
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Those capacitors are fragile and not rated for as high voltage as they really should be.

    They're also very small value caps; I don't recall offhand their values, but they're in the 1-5 pF range. They can be replaced by 500V NP0 caps.
    F4HZN likes this.
  3. N8EKT

    N8EKT Ham Member QRZ Page

    Examine each and EVERY solder connection.
    Including those covered up by foam.
    Diamond has always stretched the truth a bit on power handling but 70 watts should be fine.
    The low voltage ceramic disc capactitors are easily damaged by static discharges but more often come loose due to poor soldering from the factory.
    F4HZN likes this.
  4. KM3F

    KM3F Ham Member QRZ Page

    Look closely for rain leakage from the joints.
    If it gets in it floods the matching network and can't easily get out.
    One sign is the power meter on your radio might move value as the power remains on.
    This boils and breaks down at the network as the heat is produced changing the match impedance.
    I have a cheap version of this antenna and saw these effects until I dried the match out and taped up the joints.
    It's been fine ever since.
    If you have an Antenna Analyzer to look at both bands it may offer some clues.
    There is no replacement matching network for my antenna but Diamond might provide a replacement.
    Being a dual,band, one band might be good while the other is out to lunch.
    Its all a matter of which one get the upset in match.

    Good luck.
    Last edited: Sep 17, 2018
    F4HZN likes this.
  5. WB5TTY

    WB5TTY Ham Member QRZ Page

    I have used Diamond Dual Band antennas for about 35 years. I looked at 500HNA I put up about 30 years ago and decided to solder all of the crimped connections in the antenna. I did have a similar failure. As mentioned by others it was one of the low voltage ceramic disc capacitors that had a cold solder joint. Put the antenna back up and used it until last year. All new antennas and a new Rohn 65 Tower. The 500HNA had been discontinued so I went with the 700HNA. Soldered all the crimp connections as I did with the 500HNA. Base of the antenna is up about 65 feet with the tip at 89 feet. It does about the same as a pair of 11 Element Beams that are at 55 feet on another tower. The only advantage to the beam is noise cancelation off the sides. I run about 100 watts on VHF and 70 watts on UHF. I also have two of the DIAMOND X-6000A 144 / 440 / 1200 MHz Triband Fiberglass Base Vertical Antennas. They also work well with the local 1290 repeater. Not as much gain but will probably hold up better in super high wind. The 700HNA made it through the Texas Ice Storm of February 2021. I was very fortunate all of my beam, wire, and vertical antennas survived. 73s DE WB5TTY
    AD7SK and F4HZN like this.
  6. F4HZN

    F4HZN Ham Member QRZ Page

    Many thanks for your reply. 73s de F4HZN.

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