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N3DRB The Derb
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« on: September 12, 2008, 06:49:18 PM » |
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whats a good starting value @ 75 & 160 meters of this cap? coax inpoot through the link coil to series connected cap to ground. I presume BCL spacing would be ok for up to a few hundred watts.
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Ralph W3GL
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« Reply #1 on: September 12, 2008, 07:36:56 PM » |
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Tim,
With one of your RF Ampmeters in the input link line, you can do the old E = I x R
routine to see what the voltage is across your cap...
For very low power a BC two section should be okay but for that big Matchbox look for a cap of at least 500uuf by 1kv spacing to be in step with the 7kv caps in the box. By the way the voltage rating of the caps in the 275 watt matchbox are 3kv !
You can also calculate your approximate power with that ampmeter, assuming the coax line is 50 ohms by P = I sq x R... IE, 1 amp = 50 watts, 2 amps = 200 watts, 3 amps = 450 watts, etc...
Good luck on the MRI...
Ralph, W3GL.
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73, Ralph W3GL
"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other" Ed Morrow
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N3DRB The Derb
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« Reply #2 on: September 12, 2008, 08:08:05 PM » |
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damn ralph, I dont know why I didnt think of that. Got it and gonna js clip lead and experiment a bit.
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k7yoo
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« Reply #3 on: September 12, 2008, 09:03:39 PM » |
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I am using a motor driven 1000pf vac variable out of a defunct 180L3 antenna tuner.
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Ralph W3GL
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« Reply #4 on: September 12, 2008, 09:25:17 PM » |
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Skipper, that's just a bit of overkill !!!
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73, Ralph W3GL
"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other" Ed Morrow
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flintstone mop
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« Reply #5 on: September 16, 2008, 11:20:48 AM » |
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Hi Tim
I'm ASSuming that your typical tuna would be along the design of the famous K1JJ tuna??
The link coil in my tuner is the like the one you are describing, but no capacitor. Tom said that it wasn't absolutey necessary.
In the adjustment stage I moved the coil around within the big coil and adjusted the ant and cap taps for minimum SWR on the 50 ohm side. Always trying to shoot for 50 ohms resistive and the lowest (single digits) Xc
An ammeter (on the antenna ladder line) hookup is looking more and more inviting to me, to actually see what the heck is going out to the Ether. My signal ain't what it used to be since moving to Western Pa. I'm thinking it's miles and the terrain of Western Pa. I miss those 90 foot antenna holders/trees
Fred
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Fred KC4MOP
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Ralph W3GL
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« Reply #6 on: September 16, 2008, 02:18:00 PM » |
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Fred...
Tim (Derb) is running a Johnson KW Matchbox!
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73, Ralph W3GL
"Just because the microphone in front of you amplifies your voice around the world is no reason to think we have any more wisdom than we had when our voices could reach from one end of the bar to the other" Ed Morrow
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WA1GFZ
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« Reply #7 on: September 16, 2008, 03:01:14 PM » |
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you can never over kill a tuner with large parts. fugly and large
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Steve - WB3HUZ
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« Reply #8 on: September 16, 2008, 07:54:01 PM » |
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A typical three section BC tuning cap (300-400 pF per section) should do ya MOP. If you can get a 4-section one, even better. Also, rig up your tuna so you can go either series or parallel tuning. Much more flexible and greater tuning range. Hi Tim
I'm ASSuming that your typical tuna would be along the design of the famous K1JJ tuna??
The link coil in my tuner is the like the one you are describing, but no capacitor. Tom said that it wasn't absolutey necessary.
In the adjustment stage I moved the coil around within the big coil and adjusted the ant and cap taps for minimum SWR on the 50 ohm side. Always trying to shoot for 50 ohms resistive and the lowest (single digits) Xc
An ammeter (on the antenna ladder line) hookup is looking more and more inviting to me, to actually see what the heck is going out to the Ether. My signal ain't what it used to be since moving to Western Pa. I'm thinking it's miles and the terrain of Western Pa. I miss those 90 foot antenna holders/trees
Fred
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N3DRB The Derb
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« Reply #9 on: September 16, 2008, 08:37:12 PM » |
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nah. I forgot his call but the guy wih the 3-500Z's in the final from up there was the bomb.Anyone remember his call? I used to talk to him all the time. He was always strapping. he was just east n south fom Pittsburgh. I cant believe I cant remmeber is name or call.  |
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Ed-VA3ES
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« Reply #10 on: September 16, 2008, 10:33:57 PM » |
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W3NCC, Richard. nah. I forgot his call but the guy wih the 3-500Z's in the final from up there was the bomb.Anyone remember his call? I used to talk to him all the time. He was always strapping. he was just east n south fom Pittsburgh. I cant believe I cant remmeber is name or call. |
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"There ain't a slaw-bukit inna worl, that kin jam me!!"
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N3DRB The Derb
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« Reply #11 on: September 17, 2008, 01:55:12 AM » |
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yah thats it. is he still of this earth? I've heard nothing of him for many years now.  |
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Ed-VA3ES
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« Reply #12 on: September 17, 2008, 10:50:08 AM » |
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Don't know if he is still with us, or not. I think he ran 4-400's in his final, and the 3-500's were his modulators. He used a TV camera to watch his meters from another room. Great signals.
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"There ain't a slaw-bukit inna worl, that kin jam me!!"
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Steve - WB3HUZ
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« Reply #13 on: September 17, 2008, 09:51:21 PM » |
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The finals were 810s. The 3-500s replaced the original 304THs.
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