Really low SWRs but is it worth trimming the antenna
 

I am running a President Grant am/usb/lsb and on Channel 1 the SWR is
1:0.08, on Channel 40 it is 1:1.45 and on Channel 19 it is 1:1.09. It
really isn't worth doing an adjustment on this antenna setup is there?
The antenna is a single Yagi beam made up of two Tram Penetrators
(Monkey Made's). I think that it is sold as a 1/2 wave antenna and
have heard that it is a 5/8 wave. This antenna can be set for 10 meter
usage also. It really looks weird up there without a reflector on it.
I may put a reflector on it but am stumped as to length of the
reflector (ging to be made of 1/2" electrical conduit). I can't find
the formula for the length taking into consideration of the diameter of
the reflector. I believe that the 'stand-by' one should use 468/f.
Using 27.185 (Chl 19) the length should be 17.22 feet. Only thing is
the length of the driven element is less than 12' because of the
antennas having the centerload coil in them.

What do you think?

yes, keep trimming until the swr is 1:1.0001 or less across all the
channels. anything higher than that will absolutely fry your transmitter
and cause you to go sterile because of all the reflected power leaking out
of your rig. electrical conduit is such a great conductor that it will help
the swr also by sucking all the power that would have been reflected back
out of the coax, i would recommend 17.22329 feet, plus or minus .00001, the
tolerance is very important, a hair too long and it won't reflect properly,
too short and it will act as a director and totally reverse the pattern.

"Blue Dawg" wrote in message
oups.com...
I am running a President Grant am/usb/lsb and on Channel 1 the SWR is
1:0.08, on Channel 40 it is 1:1.45 and on Channel 19 it is 1:1.09. It
really isn't worth doing an adjustment on this antenna setup is there?
The antenna is a single Yagi beam made up of two Tram Penetrators
(Monkey Made's). I think that it is sold as a 1/2 wave antenna and
have heard that it is a 5/8 wave. This antenna can be set for 10 meter
usage also. It really looks weird up there without a reflector on it.
I may put a reflector on it but am stumped as to length of the
reflector (ging to be made of 1/2" electrical conduit). I can't find
the formula for the length taking into consideration of the diameter of
the reflector. I believe that the 'stand-by' one should use 468/f.
Using 27.185 (Chl 19) the length should be 17.22 feet. Only thing is
the length of the driven element is less than 12' because of the
antennas having the centerload coil in them.

What do you think?

On 8 Jul 2005 04:04:02 -0700, "Blue Dawg"
wrote:

I am running a President Grant am/usb/lsb and on Channel 1 the SWR is
1:0.08, on Channel 40 it is 1:1.45 and on Channel 19 it is 1:1.09. It
really isn't worth doing an adjustment on this antenna setup is there?
The antenna is a single Yagi beam made up of two Tram Penetrators
(Monkey Made's). I think that it is sold as a 1/2 wave antenna and
have heard that it is a 5/8 wave. This antenna can be set for 10 meter
usage also. It really looks weird up there without a reflector on it.
I may put a reflector on it but am stumped as to length of the
reflector (ging to be made of 1/2" electrical conduit). I can't find
the formula for the length taking into consideration of the diameter of
the reflector. I believe that the 'stand-by' one should use 468/f.
Using 27.185 (Chl 19) the length should be 17.22 feet. Only thing is
the length of the driven element is less than 12' because of the
antennas having the centerload coil in them.

What do you think?


Ignore Dave's sarcastic statement. The antenna will work very well as
is. It could be trimmed to be a little better, but you and your radio
will not notice any difference.

If it were my antenna, I would leave it up and take the time either
enjoying the radio or studying for an Amateur Radio Licenses. :)

(Had to put a plug in there.)

73 and good luck

--
73 for now
Buck
N4PGW

Blue Dawg wrote:
"What do you think?"

I gather Blue Dawg has a 1/2-wave dipole made from (2) 1/4-wave
coil-loaded whips. That works. The coils are necessary because the whips
are too short without them.

At 27.185 MHz, WL=11.035 meters=36.20 ft.

Kraus proposes a "modern version" of the Yagi-Uda antenna on page 258 of
his 2002, 3rd edition of "Antennas".

The reflector is spaced 1/4-WL behind the radiator. It could be closer
for more gain but this would make dimensions of the array more critical,
and the improvement in pattern is probably not worth it.

The reflector is 1.03 x the radiator length to get the required
inductive phase lag required of a reflector.

Length of the reflector is 0.475 WL. Length of the radiator is 0.46 WL.
Lengths of elements shrink as they get fatter and Kraus assumes thin
wires. They are also shorter with loading coils. Bandwidth improves with
fat elements and worsens with loading coils. The elements are shorter
than 1/2-WL due to "end effects".

The length of a thin non-loaded radiator for 11.35-mtr operation is 5.22
m = 17.13 ft.

The length of a thin non-loaded reflector for 11.35-mtr operation is
5.39 m = 17.7 ft.

Should you trim the antenna to optimize it? Probably not unless
performance is at least 1 dB less than expected.

Best regards, Richard Harrison, KB5WZI

On 8 Jul 2005 04:04:02 -0700, "Blue Dawg"
wrote:

It really looks weird up there without a reflector on it.
I may put a reflector on it but am stumped as to length of the
reflector (ging to be made of 1/2" electrical conduit).

Hi OM,

It's going to look quite odd with that conduit (no physical strength
to speak of) drooping in the wind. And it would look odd if it didn't
droop, being so much bigger:

I can't find
the formula for the length taking into consideration of the diameter of
the reflector. I believe that the 'stand-by' one should use 468/f.

Well ±

The formula neither takes into effect the larger diameter of your
"wire" reflector, nor its reflector size (which would be approx 5%
larger than you might expect).

Using 27.185 (Chl 19) the length should be 17.22 feet. Only thing is
the length of the driven element is less than 12' because of the
antennas having the centerload coil in them.

And your point is?

If you want an expected outcome, you do what you have to do and get on
with it. In your case, if you are seeking elegance you would then buy
two more units, clamp them base-to-base, put them about a 20th wave
behind the first two, and tune the reflector (make it bigger) by that
same roughly 5%.

If you haven't already noticed all the loose terms (about,
roughly,...) then you may think that was the end of it. But no,
there's more! How much more depends on how deep you research these
size and distance correlations, or simply take someone's word for it
and build an aircooled dummy load.

73's
Richard Clark, KB7QHC

On Fri, 08 Jul 2005 09:40:29 -0700, Richard Clark
wrote:

if you are seeking elegance you would then buy
two more units, clamp them base-to-base, put them about a 20th wave
behind the first two, and tune the reflector (make it bigger) by that
same roughly 5%.

Hi OM,

If you may notice the disparity between my post in this particular and
KB5WZI, Richard Harrison's (which is far better researched) then you
may note also his warning for element diameter (your conduit is not
"thin" by any stretch of the imagination to suit precision and text
book formulas).

73's
Richard Clark, KB7QHC

Forget the wierd remarks from the ignorant!

The VSWR is fine, assuming your measurements are reasonably accurate.

I would NOT add a reflector.

Blue Dawg wrote:

I am running a President Grant am/usb/lsb and on Channel 1 the SWR is
1:0.08, on Channel 40 it is 1:1.45 and on Channel 19 it is 1:1.09. It
really isn't worth doing an adjustment on this antenna setup is there?
The antenna is a single Yagi beam made up of two Tram Penetrators
(Monkey Made's). I think that it is sold as a 1/2 wave antenna and
have heard that it is a 5/8 wave. This antenna can be set for 10 meter
usage also. It really looks weird up there without a reflector on it.
I may put a reflector on it but am stumped as to length of the
reflector (ging to be made of 1/2" electrical conduit). I can't find
the formula for the length taking into consideration of the diameter of
the reflector. I believe that the 'stand-by' one should use 468/f.
Using 27.185 (Chl 19) the length should be 17.22 feet. Only thing is
the length of the driven element is less than 12' because of the
antennas having the centerload coil in them.

What do you think?

Why do you have to be such a putz? The man asked a question and you wanting
to feel superior to somebody, feel you have a patsy in a CBer.

More's the pity!

"Dave" wrote in message
...
yes, keep trimming until the swr is 1:1.0001 or less across all the
channels. anything higher than that will absolutely fry your transmitter
and cause you to go sterile because of all the reflected power leaking out
of your rig. electrical conduit is such a great conductor that it will
help
the swr also by sucking all the power that would have been reflected back
out of the coax, i would recommend 17.22329 feet, plus or minus .00001,
the
tolerance is very important, a hair too long and it won't reflect
properly,
too short and it will act as a director and totally reverse the pattern.

"Blue Dawg" wrote in message
oups.com...
I am running a President Grant am/usb/lsb and on Channel 1 the SWR is
1:0.08, on Channel 40 it is 1:1.45 and on Channel 19 it is 1:1.09. It
really isn't worth doing an adjustment on this antenna setup is there?
The antenna is a single Yagi beam made up of two Tram Penetrators
(Monkey Made's). I think that it is sold as a 1/2 wave antenna and
have heard that it is a 5/8 wave. This antenna can be set for 10 meter
usage also. It really looks weird up there without a reflector on it.
I may put a reflector on it but am stumped as to length of the
reflector (ging to be made of 1/2" electrical conduit). I can't find
the formula for the length taking into consideration of the diameter of
the reflector. I believe that the 'stand-by' one should use 468/f.
Using 27.185 (Chl 19) the length should be 17.22 feet. Only thing is
the length of the driven element is less than 12' because of the
antennas having the centerload coil in them.

What do you think?

Blue Dawg wrote:
I am running a President Grant am/usb/lsb and on Channel 1 the SWR is
1:0.08, on Channel 40 it is 1:1.45 and on Channel 19 it is 1:1.09. It
really isn't worth doing an adjustment on this antenna setup is there?
The antenna is a single Yagi beam made up of two Tram Penetrators
(Monkey Made's). I think that it is sold as a 1/2 wave antenna and
have heard that it is a 5/8 wave. This antenna can be set for 10 meter
usage also. It really looks weird up there without a reflector on it.
I may put a reflector on it but am stumped as to length of the
reflector (ging to be made of 1/2" electrical conduit). I can't find
the formula for the length taking into consideration of the diameter of
the reflector. I believe that the 'stand-by' one should use 468/f.
Using 27.185 (Chl 19) the length should be 17.22 feet. Only thing is
the length of the driven element is less than 12' because of the
antennas having the centerload coil in them.

What do you think?


If you worst measured swr is 1:1.45, then
don't sweat it.

You won't notice a difference between a 1:1.5
and a 1:1.1


Slick

Richard, are you saying to go buy two identical antennas and mount them
the same sans coax and then also put another reflector behind the 2nd
one, ending up with a 3 element Yagi?
Cliff


"If you want an expected outcome, you do what you have to do and get on

with it. In your case, if you are seeking elegance you would then buy
two more units, clamp them base-to-base, put them about a 20th wave
behind the first two, and tune the reflector (make it bigger) by that
same roughly 5%.
"

On 10 Jul 2005 21:53:28 -0700, "Blue Dawg"
wrote:
Richard, are you saying to go buy two identical antennas and mount them
the same sans coax...

Hi Cliff,

Put them back about ¼ wave, and tune them about 3-5% lower in
frequency = Two element yagi. If you want to chip in two more, you
can build them as directors.

73's
Richard Clark, KB7QHC

Your SWRs are great (as the antenna is setup now) dont bother fixing them.
A good antenna, maybe with some gain, usually only has a bandwidth of the 40
channels. The SWR will be maybe 2:1 at ch1 then go low to 1:1.4 at ch20 then
back to 2:1 at ch 40..will work just fine. Actually your SWRs sound too good
to me, for antennas with loading coils.

If you change the antenna the SWR WILL change so you will need to tune it
up. You want more gain, in some direction, right? well you're going to loose
gain in all the other directions. Focusing the signals by setting up the
antenna like in a beam makes the antennas SWR curve narrower, 2:1range may
only go from ch10 to ch 30. And the SWR will go up, so you need the gamma
match you see on the driven elements to fix the problem.

Apparently Peneterators are 12 ft long, with a load in the center (a lousy
compromise). There would be a matching coil at the base probably too whether
theyre 1/2 wave or 5/8th antennas. A real 5/8th antenna will be 21 ft high
with no loading coils, dont skimp on heighth .

If they are 5/8th antennas and you have mounted these base to base then you
have made an Extended Double Zepp which has gain of maybe 4-6db (2.5-4X
signal gain) and can focus the signals on the horizon (I assume these are
mounted vertically not horizontally out from the sides of a tower). you
would need to put the base to base mount at least 40ft off the ground, one
pointing up/one down.

Adding a director or reflector will not do much for you, since you already
have pretty good antenna (assuming its working right!) A Zepp antenna (end
to end 5/8th antennas, 42 ft long) is a great vertical if high enough and it
puts you power on the horizon.



"Blue Dawg" wrote in message
oups.com...
I am running a President Grant am/usb/lsb and on Channel 1 the SWR is
1:0.08, on Channel 40 it is 1:1.45 and on Channel 19 it is 1:1.09. It
really isn't worth doing an adjustment on this antenna setup is there?
The antenna is a single Yagi beam made up of two Tram Penetrators
(Monkey Made's). I think that it is sold as a 1/2 wave antenna and
have heard that it is a 5/8 wave. This antenna can be set for 10 meter
usage also. It really looks weird up there without a reflector on it.
I may put a reflector on it but am stumped as to length of the
reflector (ging to be made of 1/2" electrical conduit). I can't find
the formula for the length taking into consideration of the diameter of
the reflector. I believe that the 'stand-by' one should use 468/f.
Using 27.185 (Chl 19) the length should be 17.22 feet. Only thing is
the length of the driven element is less than 12' because of the
antennas having the centerload coil in them.

What do you think?