Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Mon, 05 May 2008 20:41:42 -0600
To which I would add the low impedance section may lead to lower impedance at the shack that may be harder to tune, but the 150 ohm line is certainly better with a 1000 ohm load than a 50 ohm line. I
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Wed, 07 May 2008 08:35:10 -0600
If you already have a balun at the feed point, this balun would keep RF from coming into the shack that the outside of the coax picked up working as a slant or vertical wire. There might be slight im
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Wed, 07 May 2008 08:45:53 -0600
Its one of the ways to increase the impedance of the outside of the coax. It allows the impedance to ground to vary on both the center and outer (inside) conductors so the antenna sets the balance. I
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Wed, 07 May 2008 08:50:49 -0600
And if you match it the same with a low loss tuner, it will work just fine for QRP. The longer length should give you some gain over an 80 meter resonant dipole. You could, but any antenna with much
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Wed, 07 May 2008 09:30:30 -0600
Ferrite always has some loss. Its the trade off between high permeability (and hence compact transformer or balun) and loss. Driven to saturation, the loss (and harmonic distortion) increases very mu
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Wed, 07 May 2008 10:25:16 -0600
Go large on the core and wire. If it doesn't get hot with a KW going through, the losses will be small. But it won't take care of the reactance from being away from the resonant frequency of the ante
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Thu, 08 May 2008 18:35:50 -0600
The middle two wires have 120 volts going to the internal switch in many Tentec radios. It would be safest to unhook them inside the power supply where you hook them together to make the power supply
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Thu, 08 May 2008 18:45:17 -0600
The fact is that the unconnected wire still has stray capacitance to space and the other wire. That causes a small current at the high impedance end of the feed line, at the antenna. And the end impe
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Thu, 08 May 2008 18:50:33 -0600
Nah, 7/16 DIN connectors are lower loss than N types. Providing you demand all the radiation be from the dipole and don't want the diversity from the feed line's radiation. So you raise and lower the
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Thu, 08 May 2008 19:09:04 -0600
"UHF" has a sturdier center connection and a very poor outer connection that depends on the tightness of the threaded ring. I've burned UHF connectors black with only 18 watts of RF at 2m when vibrat
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Thu, 08 May 2008 19:58:29 -0600
Unless I happen to make or have a UHF to BNC cable, every radio in my shack with a UHF connector has its own dedicated UHF to BNC adapter. Their loss is fairly low, and the impedance is 50 ohms unles
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Fri, 09 May 2008 18:12:56 -0600
The impedance bump is less than an inch long. If the ring is really tight, the impedance bump doesn't introduce loss so much as it introduces a change of impedance seen through the connector. At HF y
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Fri, 09 May 2008 18:47:15 -0600
My experience is that the 144 MHz signal outside 95% coverage coax is about 40 to 50 dB down from the signal inside. In applications like a repeater where the cavity set gives 90 to 95 dB of isolatio
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Fri, 09 May 2008 19:09:18 -0600
I think that was probably done back early in WW2 when the "modern" braided coax was first used in quantity. Its probably discussed in the components volume of the MIT Radiation Lab series. Somebody b
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Sat, 10 May 2008 17:27:02 -0600
It takes a significant fraction of a quarter wavelength to make a really noticeable change in the impedance. At maybe 5/8" of mismatched section, 50 pairs makes almost 32", might be noticeable on 10
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Sun, 11 May 2008 10:47:52 -0600
Ah, we tend to neglect transmission line effects. And you make a very valid point that there are many lengths of feedline can be series resonated by the high Q choke/balun. When I was at Collins we b
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Sun, 11 May 2008 10:51:16 -0600
Sometimes the higher voltage lamp was installed to lengthen lamp life. A small series resistor is effective at that task, but not as effective, but looses less light. 73, Jerry, K0CQ
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Thu, 15 May 2008 09:13:39 -0600
Seems like I've heard of a malady with the ALC blamed on the diodes. I have no personal experience about them. I don't know for sure, but that's been a common pair of techniques. 73, Jerry, K0CQ
Author: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Date: Thu, 15 May 2008 22:06:09 -0600
And while you check out their TV, notice the jumps, shakes, bars and other interference that are present while you for sure aren't transmitting because you are at their TV. 73, Jerry, K0CQ