On 11/16/2014 4:36 PM, wrote:
On Sunday, November 16, 2014 12:53:27 PM UTC-6, FBMboomer wrote:
I do not take the advice of those
who use what are supposed to be antenna modelling software that consider
all variables. They never do.

Antenna modeling is quite useful, and quite accurate as long as you
consider the possible faults, and quite useful as a learning tool.
I've modeled half a gazillion antennas, and most all were quite
accurate as long as you don't run into one of the few "gotcha's"
that can occur. That is normally not a problem with the vast majority
of antennas one would model.


Now, if a G5RV can be made to
work as well as a 1/2 wave dipole, I am guessing that it is not easily
done.

It's quite easy. Just ditch the designed for 20m feed system and
replace it with something more suitable for 75m.
The best would be to use a tuned ladder line, or a tuned open wire
line. Of course, you would need to change the lengths of the tuned
feeder if you change bands, but that can be done with knife switches,
etc..
The 2nd best would be to feed it with an untuned ladder or open wire
feeder, and use a tuner at the shack. The tuner loss won't be huge,
and it will perform better than the usual garden variety G5RV.

Myself, I would prefer to use a 130 ft dipole, and feed like this if
I were to use a tuned feeder.
http://www.w5dxp.com/notuner.HTM
But you can feed a 102 ft dipole the same way if you vary the feeder
length for a good match, with good results.

I have never heard a G5RV that was anything but lame. Perhaps
everyone puts up the G5RV using short cuts. I don't know.

No, they are just using the garden variety G5RV, which was designed
as a 20m antenna. And many use a tuner at the shack, which adds even
more loss.

Using an untuned ladder or open wire line with a tuner at the shack
should give quite an improvement over the usual 20m method most newby's
use. That's the easy way out for a decent improvement.

Now, feeding a half size dipole with the same method can lead to some
pretty serious losses if one uses a T match tuner, etc. You would want
to avoid that. I always prefer a 1/2 WL dipole for the lowest band
to be used to avoid that if feeding with ladder/open wire line and most
common tuners "IE: T match, etc" at the shack.

But I've always preferred coax fed dipoles and such. The coax fed turnstile
is one of the best NVIS antennas for the low bands I've tried so far.
Low feeder loss same as a 1/2 wave dipole, and also no tuner required.
And you can even steer the pattern a bit if you rig up a way to change
the phasing between the two crossed dipoles.

The horizontal loop is a good NVIS antenna, but I could see no real
advantage over the dipole or turnstile when considering the extra hassle
of installing one. But I wasn't worried about local noise even though
I'm in the city.
Evidently the pattern you are getting from yours has pretty low gain
at the low angles, which is likely why you are hearing less local noise.
Which is fine. But you have to consider that antennas are generally
reciprocal between transmit and receive, so if you are hearing less
noise at those lower angles on receive, you will also transmit less RF
at those same low angles. With a NVIS antenna, not really an issue though.
For DX, it would likely be inferior to the previous dipole you used.

And modeling should show you the difference between the two patterns
at those low angles quite accurately.


I have a Pixel magnetic loop with an A/B switch for receive using the
full size horizontal loop or the vertical Pixel loop. The full size loop
is almost invariably better on 75. On 40, the Pixel may or may not be
better. Mostly the full size antenna is better. On 20, 15, 17, and 10
the Pixel magnetic loop is better for me. Not always. But most of the
time. Having the A/B switch is really good for tracking QSB. For some
reason I do not understand, as the signal strength from the full size
loop decreases, the signal on the magnetic loop increases. This
phenomena is very consistent on the higher frequency bands. DX
performance of the full size loop is very good from 20 meters on up.
Perhaps the fact that the antenna is resonant with no tuner on 20, 15,
and 10 may have something to do with this. I have read that the angle of
radiation from this loop is lower on the higher frequencies.

My magnetic loop receiving antenna has a 30 db preamp. Even with this
preamp the noise floor is always lower than my full size loop. My S
meter invariably shows the noise floor at 0 on all bands.

And, yes, on 75 I do not expect and do not receive much DX. During the
day I seem to have only a 250 mile radius of effective use. And at 300
miles my signal is pretty well cut off. Of course this changes at night.
My friend with the inverted V at 200 feet is easily able to make day
contacts out to 800 miles. He has the room and 200 foot towers.

I spent 400 dollars on that Pixel antenna. It has been worth it for me.
For someone who lives in the country side with no QRN, it may not be
helpful. I have owned it for 6 months now. I did not discover the
reciprocal reception phenomena when used with my 75 meter loop until a
couple of months ago. I now take full advantage of this now on the high
frequency bands.