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M3KXZ

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Posts posted by M3KXZ

  1. Pictures:

     

    Spring removed from base:

    IMG_20140420_170126.jpg

     

    Unscrew socket retainer by holding nut in vice and tapping retainer anticlockwise with a punch:

    IMG_20140420_170209.jpg

     

    Remove socket through bottom of spring:

    IMG_20140420_170351.jpg

     

    Pleasant surprise is the BNC plug connecting coax to the socket:

    IMG_20140420_170329.jpg

     

    Hope someone finds this useful. In combination with Iain's pictures it sums up all the internals of the Plessey tuner base, which isn't really a tuner at all! I'm going to build a matching transformer into the base of mine and make a modification to the fibreglass whip to get it onto HF just because it's a nice tough base section and quite sexy looking.

     

    73

    Pete M3KXZ

  2. Iain, this was easier than I thought it would be......

     

    Removed the 6 screws that hold spring to the red insulator, held nut at top of spring in a vice, gently tapped the screw-in part that holds the connector in place anticlockwise using a punch and hammer. Once this screw is removed the connector can be removed through the base of the spring. And it reveals a nice surprise.... the coax connects into the bottom of it with a BNC plug.

     

    Pics to follow.....

  3. Whoops, almost certainly a vacuum inside so probably plug fitted in an oven. When I picked it up after removing the plug, I expected to give the base a tap and it to come off, but instead it fell off, hit the deck and pulled the coax out of the connection at the top of the spring! I now need to figure how to remove the socket at the top! Mind you, I wanted to do that anyway as part of my plan!

     

    Pete

  4. Iain, that's great. Did you find the base a pita to get off? I removed the screws but can't budge it, so need to use some force but don't want to damage it.

     

    I'm thinking about building a different choke/transformer into the base and also modifying the whip so I can fit a section or two of my Clansman whips to the top. Bottom fibreglass whip section will remain coaxial so I'll end up with something like a vertical Zepp/"no counterpoise antenna". Intention is to have something to work reasonably from 20m-6m (possibly 30-6), i.e. I can get a good enough match to 50Ohm coax such that the 3 metre run to the TS480 won't be too lossy, and then use the tuner in the TS480. I'm using SG237 at the moment, positioned right at an antenna feedthrough for a whip, but would like to do without that so I can put it to use elsewhere. Also, it keeps draining my battery when I leave it connected. I figure that the losses incurred in a decent choke/transformer and short length of coax to the rig won't be significantly different from those incurred by the small inductors in the SG237 when matching weird loads!

     

    73

    Pete M3KXZ

     

    I've now found a big enough screw driver to get the base open - internal photos at http://www.g0ozs.org/misc/Plessey_VHF_Base_Unit/ - it seems to be more of a fixed matching unit in the style of the EVHF or GSA bases than an ATU.

     

    The coax input is connected to a coiled (1/4 wave?) coaxial stub around the rim of the base, and capacitively coupled to the inner of the coax going up to the antenna. This coax inside the insulated cone is coiled around a former presumably to suppress current on the outer. The aluminium disk seems to be a solid piece of Aluminium with nothing inside - all the components are mounted on tags and pillars under the cone.

     

    I'll try to draw a diagram in due course.

     

    Iain

    73 de G0OZS

     

    [ATTACH=CONFIG]90004[/ATTACH]

  5. Hi again Iain. I see from your web site that you've pulled apart a pineapple. Just wondering, is the thread atop the pineapple same as on this Plessey base?

     

    For info, earlier on today I connected the Plessey base and fibreglass whip to my FT817. It's a pretty good match right across the 2m band. Crap on 70cm, reasonable match on 10m and lower but unsurprisingly deaf as a doorpost there!

     

    73

    Pete M3KXZ

  6. Hi Iain.

    That's also the frequency where I found a good match using the MiniVNA. I tried shoving 6V up the coax hoping I might hear something click, or maybe see some current draw, but there seems to be nothing. Putting ohmmeter across the terminal show completely open. I'm becoming more certain that there is just an RF choke or unun, perhaps on a core, and with a capacitor on the antenna feed. Will keep digging....

     

    I did email Ian, M0YMK, who is chairman of the Vintage and Military ARS in the hope that he might know something, but he has never come across this antenna before.

     

    73

    Pete

  7. Thanks chaps. I'm wondering if this might not be anything complex. I know for sure there is a capacitor in series with the element. But I'm having a feeling that there might be something as simple as an unun. There's not much room and the concave base of the tuner ring on this doesn't leave much room for electronics. Also there's a breather/dessicant thing in the base marked with an M and made by Brownell ltd. This company make these things for keeping transformers dry.

     

    Pete

  8. I hope someone can help. I have one of the antenna bases from Plessey. Reading around indicates it's for the VHF/UHF radios and the whip for it is a fibreglass centre fed one (coaxial bottom half and whip top section). I am deparately seeking one of these whips but cannot fund the NSN number for it. Actually, I want 2 of the whips as I intend to modify one of them (just the bottom section for the second whip would be fine).

     

    I have been trying to get them from an ebay seller up north (Phased_001) in North Ridings or somewhere. But he won't post due to problems before, and also doesn't want me to arrange a courier to collect as he also had problems with that a while ago. I've also tried Drop Zone down here in Sussex but they don't have any at the moment. I see Woods Group Devon are selling the bases and whips together, but when I asked them if I could have just a whip, the chap said he's sure there are some there but wanted the whip NSN! I've also tried a company in Poland whip are selling the bases and they replied saying no whips....

     

    So, please.... doesn't anyone have whips for sale?

     

    I'm also coming up with a design for similar type of whip that I can use on HF, but I need to get hold of maybe just the screw ferule/connector from the bottom of the whip to screw into the mount. So even a trashed whip would be helpful.

     

    Finally..... does anyone have any tech specs for the transformer/choke that's in this base? I know from putting it on my MiniVNA that there is a capacitor in the base, but don't know anything else about it!

     

    All help will be gratefully received....

     

    Cheers,

     

    Pete

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