G5RV trimmed for voice?
 

I was looking through the G5RV instructions including the original article,
and it's clear the antenna, when it is 102 feet long, is tuned for the
bottom of the bands. Anyone have any experience trimming one down to
resonate in the mid part of the voice bands?

--
Bruce Wilson KF7K
http://science.uvsc.edu/wilson

G5RV trimmed for voice?
 

Bruce Wilson wrote:
I was looking through the G5RV instructions including the original article,
and it's clear the antenna, when it is 102 feet long, is tuned for the
bottom of the bands. Anyone have any experience trimming one down to
resonate in the mid part of the voice bands?

If you will download the free demo version of EZNEC from
www.eznec.com, I will send you the .EZ model of a g5rv
and you can experiment to your heart's content.

The problem is if you shorten the series section to make
the G5RV resonant on 3.8 MHz, it will tend to resonate
on 40m at 2 x 3.8 = 7.6 MHz and on 20m at 4 x 3.8 = 15.2
MHz. You can always improve one band at the expense of
others.

You can improve 75m performance by installing a 1000 pf
silver mica cap across the twinlead at the twinlead/coax
junction but that cap needs to be removed for the other
bands. When I ran a G5RV, I used a clip on capacitor.
If you like 75m, try the cap.
--
73, Cecil http://www.w5dxp.com

G5RV trimmed for voice?
 

The G5RV requires a tuner, this obviates trimming the antenna for any
portion of a band.

If you look at the total antenna system (feed line length and antenna
length) you will find that shorting the antenna and leaving the feedline
length alone will result in not being able to tune the high end of the band
on 75 meters using most commercially available tuners.

If you plot all frequencies betwee 3.5 and 30 Mc you will note a large hole
just above 4 Mc where no practical tuner can create a match.

"Bruce Wilson" wrote in message
...
I was looking through the G5RV instructions including the original article,
and it's clear the antenna, when it is 102 feet long, is tuned for the
bottom of the bands. Anyone have any experience trimming one down to
resonate in the mid part of the voice bands?

--
Bruce Wilson KF7K
http://science.uvsc.edu/wilson

G5RV trimmed for voice?
 

I was thinking that maybe the efficiency of an antenna resonant at 3.5 MHz
would be poor at 3.8 MHz where I want to use it. If there is no diminution
of efficiency when the tuner fixes the impedance, then I'll just keep using
it as is.

--
Bruce Wilson KF7K
http://science.uvsc.edu/wilson
"Fred Hambrecht" wrote in message
...
The G5RV requires a tuner, this obviates trimming the antenna for any
portion of a band.

If you look at the total antenna system (feed line length and antenna
length) you will find that shorting the antenna and leaving the feedline
length alone will result in not being able to tune the high end of the
band on 75 meters using most commercially available tuners.

If you plot all frequencies betwee 3.5 and 30 Mc you will note a large
hole just above 4 Mc where no practical tuner can create a match.

"Bruce Wilson" wrote in message
...
I was looking through the G5RV instructions including the original
article, and it's clear the antenna, when it is 102 feet long, is tuned
for the bottom of the bands. Anyone have any experience trimming one down
to resonate in the mid part of the voice bands?

--
Bruce Wilson KF7K
http://science.uvsc.edu/wilson

G5RV trimmed for voice?
 

On Tue, 5 Sep 2006 18:24:08 -0600, "Bruce Wilson"
wrote:

I was thinking that maybe the efficiency of an antenna resonant at 3.5 MHz
would be poor at 3.8 MHz where I want to use it. If there is no diminution
of efficiency when the tuner fixes the impedance, then I'll just keep using
it as is.

Good choice! the receiving station will never know the difference.

Danny, K6MHE

G5RV trimmed for voice?
 

On Tue, 5 Sep 2006 18:24:08 -0600, "Bruce Wilson"
wrote:

I was thinking that maybe the efficiency of an antenna resonant at 3.5 MHz
would be poor at 3.8 MHz where I want to use it. If there is no diminution
of efficiency when the tuner fixes the impedance, then I'll just keep using
it as is.

Bruce,

I have some antenna system loss plots for a G5RV IV using different
types of feedline at http://www.vk1od.net/G5RV/index.htm .

There is a narrow optimal area around the 75/80m band, and the impact
depends on the length and grade of the coax used, ie the coax loss.
The exact frequency range will depend to some extent on your own
installation.

I would suggest that if you wanted to minimise the coax loss on
3.8MHz, you could adjust (shorten?) the dipole or the open wire
section, but that will also affect the other bands. Though it will
affect the other bands, the win on 3.8MHz might be worthwhile as the
antenna is less critical and lower loss on those higher bands on which
it performs reasonably.

Owen

PS: liked your pics, very impressive even when viewed at screen
resolution.
--

G5RV trimmed for voice?
 

Bruce Wilson wrote:
I was thinking that maybe the efficiency of an antenna resonant at 3.5 MHz
would be poor at 3.8 MHz where I want to use it. If there is no diminution
of efficiency when the tuner fixes the impedance, then I'll just keep using
it as is.

A G5RV that is resonant at 3.5 MHz would suffer additional
losses at 3.8 MHz because of the higher SWR but the ham
listening on the other end probably wouldn't notice the
difference. But for 10m, the difference between 28 MHz
and 29.7 MHz could certainly be appreciable.

Try a 1000 pf silver mica cap across the twinlead at the
twinlead/coax junction just on 75m. I think you would
like the result.
--
73, Cecil http://www.w5dxp.com