On Wed, 17 Dec 2003 07:58:25 -0700, Wes Stewart
wrote:
On Wed, 17 Dec 2003 06:44:06 GMT, Roger Halstead
wrote:
|On Fri, 12 Dec 2003 22:32:07 -0700, Wes Stewart
|wrote:
|
|On Sat, 13 Dec 2003 00:06:16 GMT, Roger Halstead
wrote:
|
||
||Every HF antenna here will go 1:1 "some where" ...
|
|Not so.
|
|I'd like to know how you can say that?
I can say it because it's true.
|
|Have you measured all my antennas?
I think an important word has been missed. :-))
No, but I've measured some of mine. Why just yesterday, I was out
measuring my vertical that started out as a Cushcraft AV-80. I'm
looking to use it on 40 meters. At resonance, at about 5.43 MHz, the
base impedance was 38.5 +j0. That's a 1.3:1 SWR.
What do your antennas have to do with mine?
And BTW that's a datum taken using a method described in HP
Application Note 77-3, "Measurement of Complex Impedance 1-1000 MHz."
I understand that.
You mistakenly believe that because an antenna *has a resonance* at
some frequency, its SWR is *1:1*. Not so, as shown above.
I don't think I used the word resonance any where in my post although
at the end I did refer to the antennas being cut according to formula
and the 1:1 point not being where the formula said it should.
I have shown at least *one* example where you are wrong when you say
*every antenna*.
Ummm...no you haven't.
Nor did I say every antenna. I said "Every HF antenna here",
paraphrased, "Every HF antenna at this location does show a 1:1 some
where in the band for which it's used".
I am speaking solely about the HF antennas at this location and was
careful to point that out. All have been checked with a Bird 43 watt
meter and each one has a point where it shows no reflected power.
Their heights and angles are such that they are non reactive at those
points, or at least as near as I can tell on a Palomar bridge and are
so close to 50 ohms I can't measure the difference.
So as the question was asked and the thread titled. "Is it possible to
have a 1:1 SWR", the answer is yes. If I can do it, so can someone
else. I didn't give any probabilities, but the odds are relatively
slim that any one throwing up a wire is going to be lucky and find it
1:1 with J=0. However if some one reads 1:1 on their bridge it
doesn't mean the bridge is necessarily bad.
I should also point out that the wire antennas here are relatively
high at an 45 degrees to horizontal. Probably not a typical
installation.
| You are welcome to come over and
|check them out.
No thanks. The weather here is much nicer for doing antenna work.
Hey, it's nicer than when I put up the tribander. I think the chill
factor was 4 degrees that day.
Current conditions:
Temperature 29 °F / -2 °C
Windchill 17 °F / -8 °C
Humidity 69%
Dew Point 20 °F / -7 °C
Wind WNW at 17 mph / 27.4 km/h
Wind Gust -
Pressure 29.70 in / 1005 hPa (Steady)
Conditions Overcast
Visibility 10 miles / 16 kilometers
Clouds
(Above Ground Level) (FEW) : 2700 ft / 824 m
Overcast (OVC) : 6500 ft / 1983 m
It's a veritable heat wave. :-)) Although we did have nearly two
inches of snow today.
| Every one "according to my meter which is a Bird"
|reaches 1:1 some where in the desired band. It may not be exactly the
|frequency the formula predicted, but it'll be relatively close.
They are cut to formula plus a tad. Shortening equal amounts did not
put the 1:1 point at the same frequency on each of the 75 meter
antennas. However both do reach 1:1 with j=0 or as near as I can
measure. The Palomar bridge isn't exactly a precision instrument.
OTOH the AV-640 Hy-Gain multi band vertical reaches 1:1 (50 ohms and
J=0) at some point on every band 40 through 6. However I'm convinced
it's a perfectly matched dummy load on 20.
Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair?)
www.rogerhalstead.com
Return address modified due to dumb virus checkers
|
|Roger Halstead (K8RI & ARRL life member)
|(N833R, S# CD-2 Worlds oldest Debonair?)
|www.rogerhalstead.com
|Return address modified due to dumb virus checkers
|