Repair a Diamond X200 VHF/UHF antenna

I bought my Diamond X200n antenna on a local ham fleamarket in october 2006. It was brand new and never used before. The antenna was mounted on the first of august.
There is about 21m of H500 coax between the transceiver and the antenna. The antenna performs well on 70cm with a very low SWR curve. On 2m however the SWR is not what I expected.
On 146.000 MHz the SWR is 2,3:1 dropping to 1,8:1 on 144.000 MHz. That could be better. My neighbour and amateur ON5NV has the same antenna, so we replaced mine to see if the problem still occurs. It may be the connector or something with the coax.

But with his antenna, the SWR was 1,1:1 on 144.000 MHz and 1,4:1 on 146.000 MHz. Perfect.

Diamond X200 capacitor detailsWe dismantled my antenna. As you can see in the picture there are two capacitors soldered in the foot of the antenna. The codes on the capacitors are 1C 500V and 9D 500V. This means 1 pF 500 volt and 9 pF 500 volt. And they’re ceramic types.
Measured the values with a meter and the 9 pF seems bad : 1,8 pF measured value. Gonna replace this one. Bought two capacitors just before Christmas 2007 on a hamfest in Bladel (The Netherlands). A few weeks ago replaced the bad C with the new one. Time to measure the antenna again.
Not what I had in mind. See this PDF document. It contains both swr curves from 2m and 70cm, one from my repeaired antenna and the other from Alex’s (ON5NV) antenna.

To be continued….

9 Comments on “Repair a Diamond X200 VHF/UHF antenna”

  1. how did your project go?? i have the same problem with my diamond x700h antenna, i was wondering if you already fixed that problem and how did you fix it. pls email me the details if possible (kennskie


    1. Recently I opened the antenne again to solder the original capacitor from Diamond back in. When opening the fibre dome a small washer fell out. The washer is the same size as the one to mount the antenna on the mastmount.
      I also noticed that the flaps of the N-connector that normally make contact with the central pin of the male connector were bend.
      After soldering and rebending the flaps I tested the antenna again. Now it seems normal on the testsetup with a pretty normal SWR curve.
      I’ll have to mount the antenna on the roof again to see if now works as it should be.

      3 unanswered questions :

      Was the washer the problem in the past ?

      Or the flaps ?

      Or bad soldering before ?

  2. I have just purchased an X200 Diamond from the estate of a deceased ham. It has a very high SWR on the 2metre section. How do you go about opening the antenna up to check and/or replace the capactors? I am very new to the repair side of our hobby and do not want to do any further damage. Thanks and 73 de Ron

    1. Below are the email messages we exchanged. I publish it here because I think that they could help others.

      Hi Ron,
      First you have to dissamble the antenna so that you have the two
      sections. In the picture see the numbers 1 and 2 in red.
      Step 3 is to unscrew the hex-key (correct term ?) in the red circle.
      There are 2 or 3 holes, but in my case just 1 hex bolt.
      Then you can slide out the N connector with the coil and the lower
      section of the antenna out of the dome gently.

      Be carefull with the hex key, it is pretty fragile.
      If it is not clear, just let me know.

      73 Joost ON3JT

      > Ronald Goodhew wrote:
      > First, many thanks for your reply Joost. We have checked everything out OK.
      > This antenna is resonate at 143Mhz. The middle of our Australian band is 146Mhz..
      > Do you know anybody that has tried to adjust the centre frequency by cutting a little bit of the element?
      > The 430Mhz is good, but at present at 146Mhz I have 1:2 S.W.R and would like to get it down.
      > I maybe can change the coax length to do this, I have not tried yet.
      > Thanks and 73 de Ron

      Hi Ron,

      sorry for the delay, pretty busy week at work. I don’t know anyone who has modified/adjust his antenna. Seems that no one has problems with it :-).
      I have found earlier a pdf form the site : with a the x200 layout and details. (probably for 144-146 but it gives you maybe some help).
      The correct download link is (the other don’t works anymore)

      In normal situations the coax-length cannot influence the swr pattern, but with RF you van get surprising results :-).

      Perhaps move the soldertap a bit on the coil ?
      Unfortunatly it stays a bit of trial and error…..

      Joost ON3JT

      > Goodmorning Joost,
      > Greetings and just to say that I have got my X200 Diamond up and working fine.
      > We used an antenna analysier to check the antenna and found it was resonate at 143Mhz.
      > SWR at 146Mhz was over 3:1. I proceeded to cut bits off the end of the inner element, about 3mm at a time.
      > When it was 26mm shorter it had an SWR of 1.15:1 on 146Mhz, which is the middle of our Australian band.
      > The SWR plot is from 1:8 @ 148Mhz to 1.1:1 @ 144 Mhz so it is working fine.
      > Thanks for all your help. 73 de Ron, VK4EMF

  3. Can you recommend some online store where I can find capacitors with values like 8pF and high voltage rating. I disassembled my Diamond VX1000 and the 8D KCK ceramic disc capacitor is blown up. I’m wondering wheren can I find a replacement part.

    1. Hi Andy,
      I found mine at a local hamfest. But I think you can find them in pretty much all online stores like RSonline ( ), but you need a VAT number I think. Try Farnell, Conrad, Radio Shack, maybe Wimo in Germany ?
      You must seek carefully, it is not a common component but it is not rare at all.

  4. I just got my x770h and it was in pieces. Can someone diret me to a site to reassemble the inner sections in the proper order. Thank you very mush
    73′ George w2agr

  5. hallo
    ik heb hetzelfde voor met mijn diamond cx4 antenne , die ik eens uitgeleend had , en niet meer werkend terug gekregen
    de man is nu overleden (een ON……) uit het antwerpse
    nu zou ik de cx4 moeten openen , doch ik zie niet goed in HOE ik dat zou moeten doen , zonder de antenne terug goed werkend ineen te krijgen .
    mag ik vragen hoe U dit gedaan hebt

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