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Hustler G7-144 vs G6-144 vs dipole radiation pattern



 
 
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  #1  
Old September 18th 07, 03:18 PM posted to rec.radio.amateur.antenna
Nate Bargmann
external usenet poster
 
Posts: 54
Default Hustler G7-144 vs G6-144 vs dipole radiation pattern

I'm curious whether anyone has run an NEC type of analysis on the Hustler
G7-144, and/or the G6-144 antennas. I'd like a gain/pattern comparison
to a 1/2 wave vertically oriented dipole. However, I can't find any
manufacturer pattern plots to compare these antennas.

73, de Nate

--

"The optimist proclaims that we live in the best of all possible worlds,
the pessimist fears this is true."
  #2  
Old September 18th 07, 07:43 PM posted to rec.radio.amateur.antenna
Dave Platt
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Posts: 464
Default Hustler G7-144 vs G6-144 vs dipole radiation pattern

In article ,
Nate Bargmann wrote:

I'm curious whether anyone has run an NEC type of analysis on the Hustler
G7-144, and/or the G6-144 antennas. I'd like a gain/pattern comparison
to a 1/2 wave vertically oriented dipole. However, I can't find any
manufacturer pattern plots to compare these antennas.


I put together a couple of NEC models for the G7-144 a year or two
ago. If I recall correctly, this antenna is composed of three
5/8-wave radiators in a collinear arrangement (stacked one above
another) separated by relatively short inductive loading/phasing
coils. It has quarter-wave radials at the bottom and is fed at the
base through a tapped coil.

I did two different models - one using shorted transmission-line stubs
as the phasing elements, and another using lumped inductances. With
the stub lengths, and the inductance values tweaked to give the
correct current-phase relationships in the 5/8-wave radiating
sections, the two models produced almost indistinguishable results in
the pattern analysis, and a gain figure which matched the
manufacturer's claims quite well. I can't claim that the models are
precisely correct, but I'd guess that they're fairly close.

The pattern seemed reasonably clean... most of the energy went
straight out towards the horizon. There were minor lobes upwards and
downwards at an angle of around 45 degrees, as one would expect from a
5/8-wave radiator. I didn't see any systematic "squint" (up-tilt or
down-tilt) in the pattern. The "donut" of the pattern was
significantly shallower than that of a half-wave reference dipole...
not s surprise.

I added a random wire down from the feedpoint to simulate the "RF on
the outside of the coax or on the mast" issue, and found that there
was little current and little effect on the pattern... according to
the models, at least, the quarter-wave radials do a pretty effective
job in decoupling the antenna from the mast and feedline.

I compared these results against those for another antenna design I've
been considering for our repeater - a pair of "plumber's delight"
copper-pipe 5/4-wave extended double Zepp antennas, stacked one above
the other (about a quarter-wave separating the tips of their inner
arms), fed in phase. The results were roughly comparable.

I've got the models on my laptop PC at home, I think... if I can find
'em I'll email them, and perhaps some results plots to you.

The biggest concern I have about the G7-144 isn't its pattern - it's
some aspects of its construction. The one we're using went bongo
after a few years up in the weather - the repeater began suffering
from extremely severe desense - it was so bad as to render the
repeater unusable unless you were within a mile or so of it. We
temporarily swapped the Hustler for a simple J-pole and got back most
of the performance.

When we tore down the G7-144 we found that the bottom end of the
base-matching/feed coil was high-Z from ground. The construction of
the antenna base depends on a heavy-gauge press fitting between two
sections of aluminum to establish the connection between the base of
the coil and the N connector, and about five years of weathering (in a
fairly mild climate) had led to enough oxidation to allow the
connection to go open-circuit at DC! I believe that there were also
some connections which were done with ring terminals and rivets. The
antenna actually worked, in the sense that it transmitted and showed a
low SWR, but there was enough micro-arcing and rectification taking
place in the oxidized connections to create plenty of broadband noise
which was swamping the receiver and leading to many dB of
desensitization.

Our chief metalworking guy tore the whole thing apart, and rebuilt the
base with a better N connector and a pair of soldered connections
between the coil base and the ground shell of the N connector. He
also cleaned up all of the sliding-tubing connections between the
radiators and phasing coils, roughened them up a bit, gooped them with
a conductive anti-oxidant compound, re-fit and re-tuned them, then
drilled through the tubing and riveted them together, and then
used heat-shrink tubing over all of the phasing-coil connections. I
think he believes in wearing suspenders, a belt, *and* duct tape :-)

We put it back up, and found that the desense was down to undetectable
levels. It's been up in the air for 18 months now, with nary a problem.

We're going to have to move our antenna tower in a few years, and at
that point we'll probably retire the G7-144 and replace it with either
a stacked pair of EDZ antennas (homebrew) or a stacked folded dipole
system (commercial). Both of the candidate designs use fully-soldered
or fully-welded radiator construction... they're DC-grounded and would
be free of sliding or press-fit connections which could oxidize and
degrade over time.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
  #3  
Old September 19th 07, 01:14 AM posted to rec.radio.amateur.antenna
Nate Bargmann
external usenet poster
 
Posts: 54
Default Hustler G7-144 vs G6-144 vs dipole radiation pattern

Thanks Dave.

That was an excellent post. It's interesting that I've read testimonials
on eHam and other web pages that claim 15 to 20 years of service with the
G7-144 with no complaints. Then there are some that have had some issues.

The G6-144 is a bit more attractive to me right now due to the lower
price and being about 2/3 of the length of the G7. Interestingly, the G6
literature (available at http://www.dxengineering.com) says, "FCC
accepted for Repeater application at 6db gain based on EIA Standard
RS-239: gain compared to 1/2 wave dipole." I've never heard of antennas
being "FCC accepted for Repeater application" before. So now I'm curious
whether the G6 may be more rugged than the G7. At the very least there
won't be so much aluminum swinging in the breeze.

I am looking for antenna for our repeater. We tried pressing a
commercial antenna tuned for 155 MHz into service, but it just hasn't
worked out as we have severe desense. Its mounting is also far from
optimal. The calculated SWR at the antenna is approximately 1.8:1.

We were checking things over today and everything looks good when the
duplexer is terminated into a 50 ohm load, but varying levels of noise
exist at the RX frequency when the antenna is connected. It is
definitely our system as the spectrum is clear when the repeater TX is
off. It was too windy today to climb to the top of the grain elevator
leg the antenna is on to check at the end of the hardline with a
wattmeter and dummy load.

I like the idea of the G6 as it appears easy to handle and easy to
mount. We are limited by the framework of the structure and we have to
avoid having anything that would get in the way of the employees or
jeopardize their safety. Also, it needs to be safe for us to work with
as well.

The G6 appears to be two 5/8 wave radiators fed with Hustler's fiberglass
encased coil assembly. I have seen that the antenna is about 10 feet
tall, weighs about 7 pounds, and has a surface area of 1.4 sq ft. We can
mount a mast easily on the structure that will support a lightweight gain
antenna like the G6. A DB-224 would be nice, but it requires
considerably more in the way of mounting and manpower resources to do it
correctly.

Any suggestions are appreciated.

73, de Nate

--

"The optimist proclaims that we live in the best of all possible worlds,
the pessimist fears this is true."
  #4  
Old September 19th 07, 03:02 AM posted to rec.radio.amateur.antenna
Dave Platt
external usenet poster
 
Posts: 464
Default Hustler G7-144 vs G6-144 vs dipole radiation pattern

In article ,
Nate Bargmann wrote:

Thanks Dave.

That was an excellent post. It's interesting that I've read testimonials
on eHam and other web pages that claim 15 to 20 years of service with the
G7-144 with no complaints. Then there are some that have had some issues.


The luck of the draw, I suppose?

The G6-144 is a bit more attractive to me right now due to the lower
price and being about 2/3 of the length of the G7. Interestingly, the G6
literature (available at http://www.dxengineering.com) says, "FCC
accepted for Repeater application at 6db gain based on EIA Standard
RS-239: gain compared to 1/2 wave dipole." I've never heard of antennas
being "FCC accepted for Repeater application" before.


I imagine that there may be some such regulations for some of the
commercial or public-safety bands? Minimum or maximum gains allowed,
or cleanliness-of-pattern perhaps?

I am looking for antenna for our repeater. We tried pressing a
commercial antenna tuned for 155 MHz into service, but it just hasn't
worked out as we have severe desense. Its mounting is also far from
optimal. The calculated SWR at the antenna is approximately 1.8:1.

We were checking things over today and everything looks good when the
duplexer is terminated into a 50 ohm load, but varying levels of noise
exist at the RX frequency when the antenna is connected. It is
definitely our system as the spectrum is clear when the repeater TX is
off. It was too windy today to climb to the top of the grain elevator
leg the antenna is on to check at the end of the hardline with a
wattmeter and dummy load.


It sure sounds as if you've got a less-than-good connection somewhere.

We had similar problems after a while with one of our "American
Legion" J-pole antennas, which use an all-aluminum construction. The
radiator and matching-arm rods were originally mounted with
set-screws, but on this particular antenna the connection had been
reinforced with a spot-weld. Due to flexure of the rods in the
breeze, the weld eventually became brittle and cracked... and the
antenna immediately exhibited severe desense due to broadband-noise
generation in the cracked junction.

Any suggestions are appreciated.


We're looking at some of Telewave's antennas, which I believe are
similar to the DB-224 in their basic design approach.

I'd also suggest that you take a look at the copper-pipe EDZ design at
http://www.tcarc.ca/public/2mdez.php, which would have gain quite
similar to the G6-144, I think.

The folks who run this page seem to like this antenna for repeater
service. Since it's a grounded, fully-soldered design (you can solder
the balun-attachment points to the matching stub) it ought to be quite
free of desense-causing corrosion/micro-arcing points.

I built one of these for our repeater system, scaled down for use as a
remote-linking antenna for the 440 band. Seems to have worked out
well so far. The only thing I'd do differently the next time I build
one, is wait to figure out the actual shorting-stub and balun
attachment points until the antenna is actually in place on the tower.
I tuned it in a free-space situation, and the presence of the tower
de-tuned it a bit (enough to notice on a meter, not enough to matter
in practice).

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
  #5  
Old September 20th 07, 01:40 PM posted to rec.radio.amateur.antenna
BB
external usenet poster
 
Posts: 1
Default Hustler G7-144 vs G6-144 vs dipole radiation pattern

On Tue, 18 Sep 2007 19:02:11 -0700, (Dave Platt)
wrote:

In article ,
Nate Bargmann wrote:

Thanks Dave.

That was an excellent post. It's interesting that I've read testimonials
on eHam and other web pages that claim 15 to 20 years of service with the
G7-144 with no complaints. Then there are some that have had some issues.


The luck of the draw, I suppose?

The G6-144 is a bit more attractive to me right now due to the lower
price and being about 2/3 of the length of the G7. Interestingly, the G6
literature (available at
http://www.dxengineering.com) says, "FCC
accepted for Repeater application at 6db gain based on EIA Standard
RS-239: gain compared to 1/2 wave dipole." I've never heard of antennas
being "FCC accepted for Repeater application" before.


I imagine that there may be some such regulations for some of the
commercial or public-safety bands? Minimum or maximum gains allowed,
or cleanliness-of-pattern perhaps?


There are none I know of. However, commercial systems are licensed by
ERP, so I would suspect that the antenna gain figures must be accurate
in order to get the ERP calculations correct.


Regards,

Bruce
  #6  
Old September 22nd 07, 02:51 PM posted to rec.radio.amateur.antenna
Nate Bargmann
external usenet poster
 
Posts: 54
Default Hustler G7-144 vs G6-144 vs dipole radiation pattern

On Thu, 20 Sep 2007 12:40:10 +0000, BB wrote:

There are none I know of. However, commercial systems are licensed by
ERP, so I would suspect that the antenna gain figures must be accurate
in order to get the ERP calculations correct.


Perhaps that is what they really mean, that the gain is certified for ERP
calculations.

73, de Nate

--

"The optimist proclaims that we live in the best of all possible worlds,
the pessimist fears this is true."
 




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