Fixing a Diamond X-500 2/70 antenna

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Fixing a Diamond X-500 2/70 antenna

Postby VK4GHZ » Thu Nov 18, 2010 12:07 am

Hi all

My 20 year old Diamond X-500 2/70 antenna stopped working earlier this year.
Not wanting to muck around, I simply ordered a new X-700 from Strictly Ham the following day.
I thought 20 years was a great run for an antenna, outside in the elements all this time.

Six months on, and I've finally found a few hours to have a closer look at the insides of the X-500, and attempt to revive it.

The antenna's construction is straight forward, but cracking the bastard open is the hard bit!
I won't attempt to post pictures of everything, because I forgot to shoot some of the steps!
(But this will give you a good idea of what is involved)

Image
Above: The brass end with the N connector screws into the aluminium base tube section.
Even clamping this in a vice, and attempting to turn the aluminium tube section failed.
The brass end screws into the tube, but is held with adhesive as well.

I found that by carefully hacksawing 5mm off the end of the tube - as seen above - made it much easier to unscrew and separate the two.
(Carefully cut around the perimeter, and use a screw driver to lever off, revealing the threaded brass end section)

Image
Above: This is what's inside! A tapped coil, a 10pF ceramic in series with coax inner, and a 1.5pF shunt.
With these standard ceramic caps, you can understand why these antennas only have a 200W PEP rating.

Image
Above: The fibreglass radome section is glued into the base aluminium tube.

Image
Above: 20 years of moisture and gunk build up inside these things.

Image
Above: Use a wire brush to remove the adhesive and gunk off the threaded end.
Ally tube in place to protect the other components whilst brushing.

Image
Above: Use a Stanley knife to get out the adhesive gunk from between the thread.
Then, using an electrical contact cleaner spray and toothbrush, everything here was cleaned.

I was fully expecting a faulty capacitor, and in order to isolate and test, I desoldered both the coil and 1.5pF capacitor from the brass joiner.

Image

Unfortunately I applied too much heat (using a large Weller 700F tip), and the end of the nylon former (on which the brass end/joiner screwed on to) became soft and melted out of shape.
(I thought real nylon wasn't meant to do this?!!!)
Anyway, to cut a long story short, I had to reform the end of this nylon former so the copper end could be screwed back on, keeping the dimensions the same.

If you are more careful than what I was, you will avoid this hassle, but I will include this detail, in case anyone else falls into the same trap.

Image
Above: The remaining nylon (I think it's nylon?) was drilled/scraped out of the brass piece.

Image
Above: Using electrical tape to form the sides, a small amount of 2-part automotive bog was used to fill in the bit that melted off!
Under this, for strength, I drilled a hole into the nylon and then banged in a small fibreglass plug (an inch or so off an old helical whip).
Around this, I added the bog.

All of this could have been avoided if I was a bit more careful in the beginning! :oops:

Image

Image
Above: the reformed end.
The new end was rounded down to size using an Ozito grinding tool, and a flat file. The brass end was tightly fitted on with a bang of a hammer!



Image
Above: A "Dremel" type tool, and this bit, was perfect for cleaning the gunk out of all the antenna's brass joining sections.
That, along with using a flat file to clean the rod sections will ensure a good electrical connection.

(My tool is actually an "Ozito" brand tool from Bunnings, which wasn't that expensive, and has many useful tips.)

Nothing had actually failed inside the X-500, but giving all the internal components a good clean/grind/file, restored the antenna to a good-as-new condition.

Enough thread was left on the base tube, allowing it to be screwed back on.
In hindsight, I was hacksaw off a smaller piece, which would leave even more thread to work with.

Once reassembled, measured SWR on 2M was 1.05:1 and on 70cm was 1.1:1, and I could trigger all the repeaters that I could always trigger/hear.
Good as new.

:D
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VK3BJM » Thu Nov 18, 2010 7:04 am

Aah - Automotive Bog; is there anything it can't do? :lol: (Apologies to Matt Groening & co...)

It's a special feeling, that sinking realisation that "I might just have completely stuffed this up with one moment's miscalculation/inattention..." :roll:

Nice recovery!!

73,
Barry
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VK3ALB » Thu Nov 18, 2010 7:14 am

Well done Adam,

How did you fit the brass base back into the aluminum tube?
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VK7DX » Thu Nov 18, 2010 9:49 am

Hi Adam,
Good job but what was actually wrong? Possibly the aluminium to brass at the thread maybe?

cheers,Frank
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VK4GHZ » Thu Nov 18, 2010 9:54 am

VK3ALB wrote:How did you fit the brass base back into the aluminum tube?

Lou, I simply screwed it back on!
There are a few turns of thread left.

In hindsight, instead of cutting a 6mm strip off the end of the tube, 3 or 4mm might have been enough to "crack the thread".

The only purpose of this thread is to hold the N-connector in place, and to withstand any downward thrust from the feedline.
With a smaller amount of thread, I will have to ensure the feedline has adequate strain relief to the mast, so the N-conn isn't pulled out from the bottom of the X-500 itself.
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VK4GHZ » Thu Nov 18, 2010 10:12 am

VK7DX wrote:Good job but what was actually wrong? Possibly the aluminium to brass at the thread maybe?

Frank, I don't know, but the SWR went noticeably high one day.
My initial thought was a capacitor had gone open circuit.

In reality, performance was probably diminishing slowly over time, as moisture entered, and the internal foam spacers deteriorated, etc.

I did try to Google this topic, to see if anyone had posted pictures before, but I couldn't find any.

Just needed a damn good clean of all the joints.
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VK2TDN » Thu Nov 18, 2010 1:35 pm

well done Adam,

I have done the occassional restoration on my X200 a couple of times .... the last time that the SWR went throught the roof, I pulled the antenna down and found many fine cracks in the fibreglass cover right up near the top of the antenna.
Years of being in the wonderful Australian sun ;)

what prob happened with yours as with mine moisture had ingressed somewhere, mine was still very wet inside, the whole length of the antenna, but in the 6 months that yours had been lying around it had dried out.

Overall they are a great antenna

Dave
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VK7HDX » Fri Nov 19, 2010 6:47 am

Hi Adam,
I have a baby X-50 which only 7 years old and is great for opening DX repeaters. But if anything goes wrong (fingers crossed) I will have a reference point now. By the way great pictures too.

73..Karl
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Re: Fixing a Diamond X-500 2/70 antenna

Postby PE2WDO » Sun Dec 05, 2010 6:11 am

Hi,
actually Dutch ham PA0FRI has 'pimped' his X510 to handle 200W+ by replacing the 500V capacitors at the base
by little pieces of teflon coax.

Image

More information on the X510 construction can be found on his website: http://WWW.PA0FRI.COM (X510 page is also available in English)

73

Willem
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VK2KRR » Sun Dec 05, 2010 7:06 am

Ive actually got a VERY long Diamond vertical mono band 2m vertical. Off hand im not sure what its called or the length but I could dig it out of the shed and find out. Its got an issue with burnt out capacitors or something of that nature in the base section. Perhaps I could look at fixing that one up to after looking at Adams posting here.
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VK2XSO » Sun Dec 05, 2010 7:57 pm

Ah ! Excellent. Thanks for the post.
My Diamond is also about 20 years old and I suspect that it will be suffering the same problems.
The SWR had been getting slowly and noticeably worse over the past year. I had swept it from 30MHz to 500MHz and noticed that the antenna's
performance is now better out of band. The antenna is down off the tower and I was contemplating taking it apart in the next few weeks.
I think that will make the task almost trivial. Thank you :mrgreen:
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VK2TDN » Sun Dec 05, 2010 8:27 pm

staying on the theme of repairing Diamond X -series antennas

I have been making repairs on a brand new Diamond X-7000 2m, 70cm, 23cm co-linear. Fred, (name changed to protect the guilty) (NOT ME) rushed into service his new antenna and jammed the sharpened solid centre core of some RG213(Benelec style) into the female centre pin of the N connector on the base of the antenna.
This, as you could imagine, damaged the splines of the centre pin.
He managed to unsolder and pull off the outer casing of the N connector from the antenna base, but was unable to effect repairs. Somewhere along the line one of the matching disc ceramic caps in the base loading section was also damaged.
The cap is a 12pF 500V, which I was able to replace. I decided to use the female centre pin from a LMR400 N connector but still had to file down the brass rod coming down from the loading section to fit into the N conn. pin.

Whilst I had the antenna apart I noticed some of the solder joints on the phasing sections were a bit "dry joined" looking so removed the old solder and resoldered, producing a nice shiney joint.
I also resoldered the full circumference of the brass to brass parts at the lower end of the base loading section (see the right side of pic 1)

below several pic of the work done...

IMGP0605a.jpg
1 ... a close up of the loading section... you can see a glimpse of the brown ceramic cap through the hole.


IMGP0606a.jpg
2 ... overall view of the base section


IMGP0608a.jpg
3 ... closeup of the filed down brass rod and the 2 female centre pins (LMR400 pin on the top)



cheers
Dave
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VK2TDN » Sun Dec 05, 2010 8:28 pm

and pic 4.....

IMGP0609.JPG
4 ... one of the phasing sections with the left hand joint resoldered


cheers
Dave
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VK2TDN » Sun Dec 05, 2010 8:31 pm

VK2XSO wrote:Ah ! Excellent. Thanks for the post.
My Diamond is also about 20 years old and I suspect that it will be suffering the same problems.
The SWR had been getting slowly and noticeably worse over the past year. I had swept it from 30MHz to 500MHz and noticed that the antenna's
performance is now better out of band. The antenna is down off the tower and I was contemplating taking it apart in the next few weeks.
I think that will make the task almost trivial. Thank you :mrgreen:



I could almost garantee that its got damp inside like my X200, commented on in an earlier post
look for cracks in the fibreglass radome near the top of the antenna that will let the rain in.
I found my one totally saturated inside, all the foam spacers had to be dried out in the sun.

Dave
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VK2TDN » Sun Dec 05, 2010 8:34 pm

VK2KRR wrote:Ive actually got a VERY long Diamond vertical mono band 2m vertical. Off hand im not sure what its called or the length but I could dig it out of the shed and find out. Its got an issue with burnt out capacitors or something of that nature in the base section. Perhaps I could look at fixing that one up to after looking at Adams posting here.


they are pretty easy to replace .... well at least the dual bands ones are. this latest tri-band antenna had the base loading coils and caps enclosed in that black plastic housing, which made it a little more difficult, but not impossible with a 400deg and resonably fine tipped soldering iron.

the disc ceramic caps are rated at 500V

cheers
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VK2TDN » Sun Dec 05, 2010 8:47 pm

I'm really hoping that the X7000 will be working again soon... as I have inherited it from "Fred" 8)
it has very respectable spec's

3 x 5/8 on 2m = 8.3dB (presumably i, it doesnt specify) gain
8 x 5/8 on 70cm = 11.7dB (presumably i, it doesnt specify) gain
14 x 5/8 on 23cm = 13.7dB (presumably i, it doesnt specify) gain

max power rating = 100W on 2m and 70cm; 60W on 23cm

VSWR < 1.5 across each band

VSWR plots show main minimums of 1.1:1 @ 145MHz ; 1.1:1 @ 435MHz and 1.15:1 @ 1285MHz

worst VSWR shown on the plots is on 23cm rising from 1.5:1 @ 1270MHz to 2:1 @ 1260MHz

cheers
Dave
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VK2XSO » Fri Dec 10, 2010 5:24 pm

VK2TDN wrote: I could almost garantee that its got damp inside like my X200, commented on in an earlier post
look for cracks in the fibreglass radome near the top of the antenna that will let the rain in.
I found my one totally saturated inside, all the foam spacers had to be dried out in the sun.


Thanks Dave,
It's never had water in it that I've found. And there doesn't appear to be any cracks or holes for water to get in. The joins would be mostly likely
for any water to get in with capillary action.

I've planned to stripp it down tonight. :)
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VK2XSO » Fri Dec 10, 2010 8:57 pm

OK... the task has been completed.

The cause of my problems was a broken 10pf capacitor. It has a small fracture that wasn't obvious until I started cleaning some gunk from around the
bottom of the flange with a soft brush. It was a little damp inside the radome, but no water as such in there. Especially after all this rain.

I didn't have to do anything complex with the bottom support tube where the connector is. Just undo the two grub screws and it slides out, coil and all.
The first element is floating at the joiner, not fixed like Adam's. The 1.5pf shunt is 2pf in mine and it earths out on the connector side of the coil, not the antenna side.

So having repaired that I took the radome off all the sections and had a look at each.
The bottom coil had been deformed from the antenna being disassembled and reassembled a few times over the years.
I took a small piece of dowel and pushed it into the coil to straighten it and set the coil back to a more even spacing.

The elements weren't corroded very much, except where the steel crimps meet the copper/brass.
The coils had a little bit of green copper oxide on them. The wire brush took care of the delicate parts and the rotary wire brush on the drill cleaned up the coils.
The straight sections I cleaned up with some steel wool.

A couple of new pieces of heat shrink over the loading capacitors and a nice thin coating of petroleum jelly over the elements and coils and it looks good.
The sponge supports have turned to s**t. Yick ! While a couple of them were ok, most of them were just horrible goo.
I replaced them with some pieces of styrofoam cut into cylinders and they work fantastic as spacers in the radome.
I can now shake the antenna and it doesn't rattle at all.

Finally some self amalgamating tape over the joiner flanges which should help keep water out just in case. :)

The SWR is fine across both 2m and 70cm, but the real results will come in tomorrow when I mount it on a pole outside and sweep it.

I've got another damaged X500 sitting in the shed that I picked up at a field day for $20. I've not had any call the fix it, I was keeping it as spare parts for this antenna. But now I might as well dig it out and check it out :roll:
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VK2TDN » Sat Dec 11, 2010 12:29 am

awesome Ash,

a good job well done :)
yeah go for broke on the other one as well give it a good refurb and get it up in the air :)
The Diamond's really are a good reliable brand, considering the hell they get in the the
Australian extreme heat etc

Dave
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Re: Fixing a Diamond X-500 2/70 antenna

Postby VE2AW » Mon Feb 14, 2011 9:09 am

Hello everyone,

This indeed was a very fine and informative posting by Adam and which will be of great use to me. I happen to own a similar antenna and mine also appears to be in the same condition that Adam's antenna was in, before he attempted to revive his.

Mine is currently stored in three parts each, for both the antenna elements and for the radome.
Problem now is that I don't know which of the elements is the center and which is the upper element...

Would anyone, by any chance have either a schematic diagram or possibly a picture of the layout of the elements? I have been looking for the information for approximatly two years and today is my lucky day as I came upon your Discussion Forum.

Many thanks for your time and 73.

Gerry VE2AW
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