On Sat, 12 May 2007 20:48:44 -0700, Roy Lewallen
wrote:


It would be really neat if we had a tuner that would selectively tune
the signal and noise. But alas, we don't. At HF, the signal and noise
are both coming from outside the antenna, so anything we do at the tuner
-- or anywhere between the antenna and receiver -- affects both equally.
The tuner won't affect the received s/n ratio unless you get it so badly
mistuned that you start hearing receiver noise, which isn't likely at
HF. So tune it any way you want.

For transmitting, you're always best off getting as much power to the
antenna as you can. (I mean actual power, not "forward power".) What
you're trying to do is make the best s/n ratio at the other guy's
receiver. You can't do anything about his noise, but for every dB you
increase your signal, you get a one dB improvement in the s/n ratio at
his end. This means having an SWR low enough that your rig doesn't shut
down. Unless you have an extraordinarily lossy transmission line, any
SWR below the shutdown point will get the same amount of power to the
antenna for practical purposes.

At VHF and above, receiver noise is usually greater than atmospheric
noise, so the rules change for receiving antennas. There, you do want to
get as much signal from your antenna as you can in order to get the best
s/n ratio. The rule for transmitting is still the same, though.

Roy Lewallen, W7EL

Thanks, Roy,

A friend of mine suggests I setup a field strength meter and tune for
maximum fs. I don't usually use baluns so I would wonder how accurate
that would be.

Currently, I am tuning my gutters up for HF. I checked it with an
analyzer the other day and found it is an excellent 160 meter and 20
meter antenna without the tuner (swr-wise). In the meantime I am
building a vertical for 20 and up.

Thanks again,
73 for now,
BUck
N4PGW

--
73 for now
Buck, N4PGW

www.lumpuckeroo.com

"Small - broadband - efficient: pick any two."

"Rick (W-A-one-R-K-T)" wrote in message
news
On Sat, 12 May 2007 09:27:47 -0700, herbert.don wrote:

how far apart are the ends?

Around 235 feet.

Is there a reason you are using a 160 m antenna on 40/80 meters? A shorter
antenna would get the ends a lot higher, assuming you used the same end
supports.

Tam/WB2TT

On Sun, 13 May 2007 09:26:13 -0400, Tam/WB2TT wrote:

Is there a reason you are using a 160 m antenna on 40/80 meters?

So I can get decent results on 160.

"Rick (W-A-one-R-K-T)" wrote in message
news

I just put up an inverted V that is up about 70 feet in the center and
about 15 feet at the ends. Each leg is about 130 feet long, or about 260
feet overall, which is right around a half wave for 160 meters. It is fed
with ladder line and an LDG auto-tuner.

I also have a dipole antenna that's up about 17 feet and is a half wave
for certain MARS / CAP frequencies above the 75 meter band, hence it's a
bit short for 75 meters. That antenna is coax fed and goes through a
different LDG auto-tuner which allows me to use it on 75/80 meters with a
good match.

The long and high inverted V doesn't work any better than the short and
low dipole, and in some cases doesn't work as well.

I have checked all the connections on the inverted V and even did a
continuity check from each side of the ladder line, up through the feed
point, out each leg to the end of each leg, and all seems OK.

I have tried switching auto-tuners (taking the one that's on the coax-fed
dipole and putting it on the inverted V) with no discernible difference.

Seems very strange. Any ideas that might account for why the V doesn't
work better?


One of the bad things about stationary high gain antennas . It may have gain
out the wazoo but if its not putting the signal in the right place it doesnt
do much good.

Jimmie

Buck wrote:

A friend of mine suggests I setup a field strength meter and tune for
maximum fs. I don't usually use baluns so I would wonder how accurate
that would be.
. . .

That's a perfectly good way to adjust a tuner, providing the meter is
far enough away from your transmitter that direct leakage radiation from
the transmitter and line between it and the tuner aren't making a
significant difference. As long as it is, it doesn't matter if you have
a balun or not, or whether your feedline is radiating or not. Adjusting
the tuner has no effect on how your system radiates, just how much. The
field strength meter is sampling just one part of the overall pattern.
But adjusting the tuner increases or decreases all parts of the pattern
in proportion, so the field strength meter tells you what you want to know.

A field strength meter isn't, however, usually a good way of judging
whether a change in the antenna (as opposed to a tuner adjustment) is
good or bad. This is because changing the antenna does affect the
pattern, and the field strength meter only tells you what's happening in
one direction -- and likely in the near field, to boot.

Roy Lewallen, W7EL

Buck wrote in
:

Currently, I am tuning my gutters up for HF. I checked it with an
analyzer the other day and found it is an excellent 160 meter and 20
meter antenna without the tuner (swr-wise). In the meantime I am
building a vertical for 20 and up.

I don't know if there is a different meaning for the term gutters on your
side of the big pond, but if you mean the parts of a building for
collecting the rainwater from the roof...

Roy has talked to you briefly of the near field / induction fields. The
closer you place your antenna to noise sources (eg appliances, including
switched mode power supplies), the greater the response of your antenna
to those sources.

You have probably heard of the square law of light that tells you that
the power density of an EM wave decreases with the square of distance.
That is true in the radiation far field, but in the near field, the
induction fields decay more rapidly that that, and every bit of distance
you can put between your antenna and noise sources is worthwhile.

Wrapping your noise sources with your antenna sounds a sure fire way to
couple the very most interference... is that what you really want to do.

Owen

On Sun, 13 May 2007 22:41:49 GMT, Owen Duffy wrote:

Buck wrote in
:

Currently, I am tuning my gutters up for HF. I checked it with an
analyzer the other day and found it is an excellent 160 meter and 20
meter antenna without the tuner (swr-wise). In the meantime I am
building a vertical for 20 and up.

I don't know if there is a different meaning for the term gutters on your
side of the big pond, but if you mean the parts of a building for
collecting the rainwater from the roof...


Yes, gutters are the rain collectors/diverters. I live in a duplex
apartment with gutters that go from just outside my back door, up the
wall two stories, across the roof edge for two apartments and down to
just above the ground on the far wall of the apartment.



Roy has talked to you briefly of the near field / induction fields. The
closer you place your antenna to noise sources (eg appliances, including
switched mode power supplies), the greater the response of your antenna
to those sources.

You have probably heard of the square law of light that tells you that
the power density of an EM wave decreases with the square of distance.
That is true in the radiation far field, but in the near field, the
induction fields decay more rapidly that that, and every bit of distance
you can put between your antenna and noise sources is worthwhile.

Wrapping your noise sources with your antenna sounds a sure fire way to
couple the very most interference... is that what you really want to do.

No, but until I build the vertical, it is all I have to work with.
This is a 'cliff-dweller' situation.


Owen

Thanks for the responses. I appreciate them.

Buck
N4PGW

--
73 for now
Buck, N4PGW

www.lumpuckeroo.com

"Small - broadband - efficient: pick any two."

When an inverted V gets long with respect to wavelenth, the main lobe
elevates pretty dramatically, so you no longer get a decent take off
angle...lots of radiation at high angles, but very poor at the lower angles.

I found this precise problem when trying to run inverted vee's as extended
double zepps...they don't work very well compared to the same antenna as a
flat top.

All I had to do was model the V using EZNEC, and sure enough a 3D display of
the pattern showed the problem. The nice gain lobes I was looking for were
missing in the 2D display at the elevation angles I had expected. Going 3D
showed me where they went...way high, not very useful for what I wanted.

The moral of the story: if you want long (w/r to wavelength) dipoles to be
effective at low angles, only use flat top configuration. Inverted V's don't
do well as they get long with respect to wavelength.
"Rick (W-A-one-R-K-T)" wrote in message
news

I just put up an inverted V that is up about 70 feet in the center and
about 15 feet at the ends. Each leg is about 130 feet long, or about 260
feet overall, which is right around a half wave for 160 meters. It is fed
with ladder line and an LDG auto-tuner.

I also have a dipole antenna that's up about 17 feet and is a half wave
for certain MARS / CAP frequencies above the 75 meter band, hence it's a
bit short for 75 meters. That antenna is coax fed and goes through a
different LDG auto-tuner which allows me to use it on 75/80 meters with a
good match.

The long and high inverted V doesn't work any better than the short and
low dipole, and in some cases doesn't work as well.

I have checked all the connections on the inverted V and even did a
continuity check from each side of the ladder line, up through the feed
point, out each leg to the end of each leg, and all seems OK.

I have tried switching auto-tuners (taking the one that's on the coax-fed
dipole and putting it on the inverted V) with no discernible difference.

Seems very strange. Any ideas that might account for why the V doesn't
work better?