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   Home   Help Search  
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 1 
 on: Today at 07:49:28 AM 
Started by N9MXY - Last post by WX7G
The antenna in question is called a 1/4 wavelength ground plane. What is it actually? Because the radials slope downward it is a vertical dipole. The amount of radial radiation and element radiation is proportional to their vertical length. For 45 deg sloping radials the radials radiate 41% of the energy while the element radiates 59%.

What does grounding the antenna the antenna do? Given the correct length wire in the grounding path, and a low impedance ground, the ground current could be as high as 25% of the antenna current. This can have an effect on the radiation pattern and loss. The reduction in signal could be as high as 1 dB.

 2 
 on: Today at 07:46:40 AM 
Started by JS6TMW - Last post by JS6TMW

That's a lot of good information there. The silicone grease I acquired today is marketed for scuba gear. It has a very faint acetic acid odor like silicone caulk. I had a half a tube of Dow Corning silicone grease in my toolbox for about 30 years but pitched it when I moved to Japan. I used it on distributor caps now and then.

So I think I'll try it out first on new rotator cable connections, where it is easy enough to see if it is doing any harm. I have plenty of Coaxseal and self-sealing tape for everything else, but the article encourages me to try a dab on the coax connectors.

Steve in Okinawa

 3 
 on: Today at 07:37:16 AM 
Started by ZL1BBW - Last post by KC7YE
Had QRZ as ring tone on "old" phone that died, New Apple i phone now has CW "phone call" & "text". Does open conversations with people around when get call. Is that Morse code ? etc. Plus I can hear them while working.

 4 
 on: Today at 07:33:49 AM 
Started by W5JON - Last post by K1ZJH
Amplifier gain is a separate issue from amplifier IMD. In terms of gain, it doesn't matter whether that extra gain from low level stages is in the output stage of a 100W transmitter, or in an outboard Amp after a QRP transmitter.

But I do agree - maybe it's time to consider more stringent TX IMD and Amplifer IMD regulations. Although we likely won't want to pay for it.

You hit the nail on the head.  But regardless, any idiot can overdrive an amp, or run the mike gain too high.  It is pretty hard to idiot proof the hobby.  But, basic parameters such as IMD and ALC overshoot probably need to be regulated, since the manufacturers don't seem to care.

 5 
 on: Today at 07:33:12 AM 
Started by N9MXY - Last post by WB6BYU
Quote from: N9MXY

...since the antenna is isolated from ground the counterpoise seems to have a much greater effect on the resonant frequency than if they were grounded. 



They certainly do affect the resonant frequency.  You basically have
a vertical dipole with the bottom half widened out. You can tune it by
adjusting either end, which is handy because the bottoms of the radials
are often easier to reach.  Adjusting the relative lengths of the top and
bottom sections changes the feedpoint impedance, and is one tool for
matching.

And, yes, it's just a vertical ground plane with sloping radials. Just
because it can have a variety of names doesn't change how it works.


Quote

...the un grounded radials provide a "sheild" from ground at the resonant freq...



The ground is still significant.  Though the immediate ground losses will be somewhat
lower (primarily due to more distance) the low angle radiation still depends on the
local ground conditions out to 50 - 100 wavelengths.

 6 
 on: Today at 07:33:12 AM 
Started by KB4MNG - Last post by AE5X
I remember the Bobcat!  Great idea, good ergonomic design for woodland use and radically ahead of it's time.  Unfortunately, like many good ideas, served to early, it did not pay for it'self at that time.

Glad to hear it, Ray - the number of those who know of this rig has now doubled! I'm on a mission to prove this rig existed, scouring old QST and 73 magazines of the period, as time allows.

 7 
 on: Today at 07:26:11 AM 
Started by NT6U - Last post by N4UM
Enough with  the ad hominums(sp?) already.  This isn't an election .

 8 
 on: Today at 07:09:24 AM 
Started by KC1FVF - Last post by VE3LYX
I have begun a slow but deliberate move to use slug tuned coils and fixed capacitors in my vfos. Even crystal controlled Txs vaccum tube tank circuits. I am very happy I did. They work very well, sometimes much better then a variable cap and tuning rate is always comfortable.
Otherwise I have bought the Chinese polycons (recent quick and easy GDO project. FET with LED indication) And Midnight Science (Crystal Set Soc) has some very good reduction drive air variables that one would find a joy to use.
donVe3LYX

 9 
 on: Today at 07:06:15 AM 
Started by KG7LFJ - Last post by KB0TXC
I got the 4BTV as I was really interested in 20 and 40 meters. I anchored mine into the ground with a 2 inch iron pipe driven four feet with a foot and 4 inches left out of the ground. I also recommend the tilt option. I tilt mine down each year to inspect the plastic part and replace the top cap. I also take the opportunity to wipe down the antenna and check the clamps for tightness.

I have forty radials, and someday would like to put in another forty. I used the metal staples. If you live in an area like I do with lots of storms, you might consider what I did for lightning protection... I put a ground rod next to the mounting pipe, and then four more at the cardinal points at fifteen feet all connected with heavy copper ground wire, everything silver soldered as well as clamped. I do not count those as RF radials.

Best,

Joe KB0TXC

 10 
 on: Today at 07:00:25 AM 
Started by N2EY - Last post by N2EY
From http://www.arrl.org/fcc-license-counts

the number of current unexpired FCC issued amateur licenses held by individuals on July 27, 2016 was:

Novice:               10,399   (1.4%)
Technician         368,466   (49.8%)
Technician Plus            0     (0.0%)
General             172,177  (23.3%)
Advanced            46,226   (6.2%)
Extra                 143,219   (19.3%)

Total                 740,467

Percentages may not add up to exactly 100.0% due to rounding.

No new Novice or Advanced licenses have been issued since April 2000. However, the totals for those classes may sometimes show an increase over prior numbers due to renewals in the grace period.

This is a new record high total.

73 de Jim, N2EY


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