BOOKMARKED! :mrgreen:
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BOOKMARKED! :mrgreen:
I've been interested in building variable capacitors but I also see this as a bit esoteric for me at this time. I will continue to read up on it though.
Need Vcaps? Hamfest, hamfest, hamfest usually 5 bucks. I have also bought them in package deals on ebay.
Now if you're really good, consider sheet metal and plywood. Do your mock up on cardboard first. Yeah, I could easily spend on tools but once you got'em ...
Good luck finding the really large - useful at QRO - ones.Quote:
Originally Posted by KG4CGC
I have in my possession a 200pF/section, 50kV spacing butterfly variable. Big Rat Bastich.
No, it isn't for sale.
Plans are to build a remote tuner for a sloper array that I hope to construct some time in the next few years.
Thank you sir and good luck to you as well LOL!Quote:
Originally Posted by N8YX
They're there but it's like fishing.
I got hold of a couple at Dayton a few years ago. Where I really made out was on some big, honkin' 6 and 8-position, 5-deck ceramic band switches. 5kW+ units in anyone's book.Quote:
Originally Posted by KG4CGC
$1.00/ea.
'DSG was mumbling "WTF?" up until I showed her how much the things were fetching online.
Ok, dumb question then. At 100W out, do I need butterflies, or can I get away with those little trimmer ones you find in radio's?Quote:
Originally Posted by N8YX
Use the formula shown above, measure the plate spacing and determine the breakdown voltage. If the trimmer units are even close to 1kV spacing, they'll work. (IIRC, the output loading caps in a couple of my amps use 750v spacing @ 600w PO - but they will arc over if the amps are loaded incorrectly.)Quote:
Originally Posted by KC2UGV
Most of the trimmers used in BC receivers are of the 100v (or less) variety and use Mylar as a dielectric. Good for QRP; certainly not good for 100w network input power if attempting to match a high-impedance load.
Ah, got it. On with the butterfly then :)Quote:
Originally Posted by N8YX
Ok, so I still plan on building a transmatch (Something about the making it, just does it for me), but for now, I found one I couldn't pass up:
Antenna Transmatch = $5
It's made by Ascom, looks to be about 25-30 yrs old, and came from an SK estate. All it says,"AS (ascom) Antenna Transmatch".
Have no idea yet what the specs are, but I'll figure it out from estimates, or I'll scrounge up a full circuit tester (Cap meter, inductance meter, etc).
I opened it up, and man, short of the plastic side panels, this think looks like it was built like a tank. Two butterfly caps (Have to be small rated, gap of about 1/16" or 1/32"), and it's a T network, I think.
And, I got my first Heathkit. A dummy load :lol: $5
I guess I'm curios why you latched on the T network. An L network is easier to build, has practically the same impedance matching range and one other key operational advantage. A T network can, under certain load conditions become a high pass filter and will provide a false SWR indication. That is, the SWR meter will tell you that your system is tuned when it is not. Finding the right LC comination on a T network can be challenging because of this. A L network will only provide a match at the correct setting. Like I already said, some of the best transmatches ever made like Drake and Ten Tec use the L network. People have a mistaken notion that because something is simple it can't work well when in this case it is just the opposit. To provide a conjugate match you Xl (inductor) and Xc (capacitor), the L network gives you just that. Try it an see if I'm right......
And one more thing, for a 100 watt rig a capacitor plate spacing of 1/16 inch is more than adequate.