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Author Topic: 500 Watt Hamsticks?  (Read 5953 times)
W8JX
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« Reply #15 on: July 19, 2011, 04:10:09 PM »

I used to use about a 100pf silver mica at base of hamstick on 20 and 17 and 250pf on 40m.  I had them setup so I could change them easily when I swapped sticks.
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N3OX
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« Reply #16 on: July 19, 2011, 05:41:21 PM »

To quote G3YXM
"A good big mobile whip on resonance on the LF bands will present an impedance of about 20 Ohms to the rig, it won't like this!

I bet it will like it fine if the transmitter is a solid state PA like the one G3YXM uses Grin  I built one of those and was actually considering using three parallel coaxes (16.67 ohms Zo) out to my ~17 ohm base loaded 160m vertical.  I was having a hard time getting a higher ratio transformer to transform 50 ohms down  to the couple ohm impedance of the power supply because of leakage inductance in the transformer, then I realized I was stepping up and back down and didn't have to Grin

I would have had to build a 17 ohm characteristic impedance low pass filter as well as modifying the feeder out to the antenna (which was multiband with switched matching to 50 ohms on all 160 through 30m) so I never did try it... but if you were building a solid state amp and antenna it might not hurt to deviate from the 50 ohm standard.

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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
K0BG
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« Reply #17 on: July 20, 2011, 06:44:47 AM »

Biggest problem with capacitive matching, is the antenna isn't DC grounded. If you lived out here in the desert SW, you wouldn't use caps, you'd use a shunt coil. Rolling and dust static take their toll, don't you know?

What's more, a properly adjusted shunt coil doesn't have to be readjusted when you change bands. This is also why it is the best method for a remotely tuned antenna.
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W8JX
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« Reply #18 on: July 20, 2011, 09:43:51 AM »

Biggest problem with capacitive matching, is the antenna isn't DC grounded. If you lived out here in the desert SW, you wouldn't use caps, you'd use a shunt coil. Rolling and dust static take their toll, don't you know?

In the past I traveled the west and south west extensively many times using mobile HF and never had a static problem other than power line noise at times just like back here.
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K0BG
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« Reply #19 on: July 20, 2011, 01:36:13 PM »

Well, you can't say you're not lucky!

I even have to use a static drain. The looped cap hat took care of the corona problem too. And as I said before, a shunt coil has a lot more attribution, especially if you operate a remotely tuned antenna.

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W8JX
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« Reply #20 on: July 20, 2011, 07:55:32 PM »

I am curious. Is it the lower average humidity that can cause that problem at times?
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W5DXP
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« Reply #21 on: July 21, 2011, 08:13:17 AM »

I am curious. Is it the lower average humidity that can cause that problem at times?

Yes. I had a severe p-static problem in Arizona but no problem in East Texas.
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K0BG
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« Reply #22 on: July 21, 2011, 10:58:34 AM »

Modern vehicles use metallic brake shoes, and graphite in the tires to bleed off static. All well and good, but the bleed off is less than optimal when the humidity hovers around 5% to 10%, and the temp ≈100°.

The static drain I use is a piece of 3/16 aircraft cable, flayed at the bottom end. It is long enough to be the last thing is the slip stream. There are times here in Roswell, that if you fold the drain back under the rear facia, by the time you roll 200 feet, all you hear is a roar. Drop it back down, and you get an occasional pop as the charge dissipates.

The other issue with using caps to impedance match, is the antenna isn't DC grounded. That might not make any difference to you, but it does to me. It affords some protection from lightning (in 40+ years I've been hit three times), helps bleed off static build up on the antenna, offers some protection from low-hanging overhead wires. And, I don't have to change the value when I change bands.
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W8JX
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« Reply #23 on: July 21, 2011, 03:09:12 PM »

The other issue with using caps to impedance match, is the antenna isn't DC grounded. That might not make any difference to you, but it does to me. It affords some protection from lightning (in 40+ years I've been hit three times), helps bleed off static build up on the antenna, offers some protection from low-hanging overhead wires. And, I don't have to change the value when I change bands.

Well if my mobile actually gets hit by lightening I do not think it is going to matter much if it is grounded nor not as I will have bigger problems as it will likely knock out car systems too.
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You can embrace new computer/tablet technology and change with it or cling to old fall far behind....
K0BG
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« Reply #24 on: July 24, 2011, 06:20:10 AM »

You might be surprised.

In 2007, on the way back from Dayton, I got hit by lightning about 1 mile east of the NM line, on 70. The hood of my Ridgeline turned bright blue, for about 5 seconds, and the thunder clap was nothing short of thunderous! My 7000 was on at the time, listening to NOAA radio, as I had already driven through western Oklahoma less than 20 minutes after a tornado touched down. The radio continued to work, but about 18 inches of the HF whip was burned off, the solder in one lug attaching the matching coil was blown out, and the static drain was no longer in evidence. There were little balls of metal in the bed, assumingly from the whip, and the one inch corona ball.

This strike was the third time I've been hit over the years. The first strike destroyed a Standard 2 meter transceiver, but the NCX3 I was using at the time survived. The second one didn't do any radio damage, but did blow out one tire.
« Last Edit: July 24, 2011, 01:35:30 PM by K0BG » Logged

K5LXP
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« Reply #25 on: July 24, 2011, 07:31:59 AM »

This strike was the third time I've been hit over the years.

1. Is that a hint?
2. Remind me never to take a trip in your car.
3. Suggest you get some lottery tickets.

:-)


Mark K5LXP
Albuquerque, NM
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