Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Sun, 13 Feb 2011 19:12:17 -0600
One side of the dipole and the feed makes 76 feet, not far from 66 feet which would be a half wave on 40. Even with the slightly short radiator on 40, it makes a low impedance that transforms through
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Sun, 13 Feb 2011 20:00:21 -0600
That is an effective but sometimes inconvenient way to handle an antenna and feedline that gets the feed Z out of the range of the tuner, a significant problem with the limited range of the Johnson M
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Sun, 13 Feb 2011 23:04:55 -0600
That's one way to increase the matching range of the Matchbox. Another is a variable series capacitor on the input coil or link. Those other things with the feed line are other details that work to s
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Mon, 14 Feb 2011 10:07:12 -0600
How do you KNOW "that matchbox" has no coil to tap? If its a Viking Matchbox its a link coupled with an input coil. He didn't say what kind of match box. 73, Jerry, K0CQ Besides, it is not as good to
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Tue, 15 Feb 2011 14:24:37 -0600
Usually, in a T tuner, more inductance is lower loss from lower loaded Q and so greater bandwidth. Usually lower inductance means a higher loaded Q, greater circulating currents, and so greater loss
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Wed, 16 Feb 2011 11:16:35 -0600
When loading a high impedance line with a low impedance antenna (a nearly half wave antenna, like yours on 40m is low impedance) a quarter wave of line gives you a very high impedance. That antenna h
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Wed, 16 Feb 2011 11:35:22 -0600
No, the SWR does NOT change along the line. The voltage and the current changes with the SWR is high. The proper term is "where the tuner is clearly at an extreme VOLTAGE point on the feeder, ..." 73
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Wed, 16 Feb 2011 17:01:21 -0600
There's good math for all occasions of antennas and feedlines. You need to know the feed impedance of the antenna at all frequencies of interest. And as a first approximation you can figure if the fe
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Thu, 17 Feb 2011 23:18:10 -0600
Check for a leaky filter capacitor. Check for loose transformer assembly screws, which can also be the mounting screws. Check for a steel case close to the core, maybe touching. Might take some stuff
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Fri, 18 Feb 2011 13:55:29 -0600
I think you will find the whip, loading coil and capacity hat make a series resonant circuit on 80 meters. Much like a base loaded mobile whip and coil. That is will make most any short length (much
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Fri, 18 Feb 2011 14:49:07 -0600
Yah, I'm going to LEAP in here. First its Jerry, not Gerry. Its been Jerry all my life and I'm not changing now on my 69th birthday. I don't know my mother's reasoning, but that's the way it is. I do
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Fri, 18 Feb 2011 14:52:56 -0600
High voltages and circulating currents aren't a problem if the parts are big enough. They are a problem in a compact or budget tuner. 73, Jerry, K0CQ This quote from G3RZP on another forum: "The KW10
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Sat, 19 Feb 2011 00:02:01 -0600
Mouser and Digi-Key have no minimum order and have the real Amphenol. Radio Shack probably has them too. I see Mouser and DK have them in stock, with Digi-Key wanting an unreasonable price for the ge
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Sat, 19 Feb 2011 18:57:26 -0600
The waterfall display is very handy finding signals on a nearly dead band, especially VHF and microwave (where lacking frequency stability and precision might find a station more than a few kHz away
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Mon, 21 Feb 2011 22:49:18 -0600
RF Parts shows the 2SC2290 having the same characteristics as the original MRF458. On their price list they say call for MRF458. For the driver pair of MRF476 their price list says sub with 2SC2166.
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Mon, 21 Feb 2011 23:41:36 -0600
The fine Orion II manual says: Carrier amplitude for AM operation is set automatically by ORION II. The PWR control on the front is used for PEP output power setting in AM operation. A value of 100 w
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Tue, 22 Feb 2011 10:56:01 -0600
The power switch does nothing in the radio, just goes to the power supply connector on the back. Momentary contact switches are unusual on the gain control. Might there be a bug in the works literall
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Tue, 22 Feb 2011 11:34:34 -0600
Don't rule out TenTec as a parts and crystal supplier. 73, Jerry, K0CQ Power switch won't stay "on". My Omni D/B is push for "on", which matches the manual's description for this Omni C, this one is
Author: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Date: Tue, 22 Feb 2011 12:20:33 -0600
That quote would be definite disincentive. 73, Jerry, K0CQ 73, Jerry, K0CQ Power switch won't stay "on". My Omni D/B is push for "on", which matches the manual's description for this Omni C, this one