Lightweight yagi antennas as a design philosphy
 

Is anyone engaged is a design philosophy that seeks the design of VHF yagi's
with the smallest acceptable diameter of elements?

What you are trying to do is to design lighweight VHF yagis, you are seeking
how small you can go with element diameters before performance begins to
suffer.

"Richard" wrote in message
...
Is anyone engaged is a design philosophy that seeks the design of VHF
yagi's
with the smallest acceptable diameter of elements?

What you are trying to do is to design lighweight VHF yagis, you are
seeking
how small you can go with element diameters before performance begins to
suffer.

Richard,
I think if it is heavy enough to physically support itself, it will be
electrically OK. This turns out to be about 1/4 inch (6 mm) tubing at 50
MHz, and 1/8 inch (3mm) hard aluminum rod at 144 MHz and above.

Tam/WB2TT

Richard wrote:
Is anyone engaged is a design philosophy that seeks the design of VHF
yagi's with the smallest acceptable diameter of elements?

What you are trying to do is to design lighweight VHF yagis, you are
seeking how small you can go with element diameters before performance
begins to suffer.

You can still buy the old Flexa-Yagis that use very thin, springy
elements made from stainless steel.

Skin losses in the stainless steel cost about 1dB at 144MHz, but no
lower-loss material has the mechanical strength to survive the loading
from ice or optimistic birds.

Very thin elements are also a serious danger to eyes and, er, other body
parts.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

"Tam/WB2TT" wrote in message
...

"Richard" wrote in message
...
Is anyone engaged is a design philosophy that seeks the design of VHF
yagi's
with the smallest acceptable diameter of elements?

What you are trying to do is to design lighweight VHF yagis, you are
seeking
how small you can go with element diameters before performance begins to
suffer.

Richard,
I think if it is heavy enough to physically support itself, it will be
electrically OK. This turns out to be about 1/4 inch (6 mm) tubing at 50
MHz, and 1/8 inch (3mm) hard aluminum rod at 144 MHz and above.

Tam/WB2TT

Thanks. Of course over the years I'm used to seeing commercial TV and FM
antennas which tend to use 3/8" and greater for elements and because just
recently I've been comimg across designs using 4mm tubing it seems odd to
me. As if there's just got to be some big losses or compromises on using
say 4mm dia rod. But I now see that quite standard of course to use 3 and
4mm elements for high band VHFyagis. All is rather new to me. I should be
seeing 4mm rod as the norm for a VHFhigh band yagi.

"Richard" wrote in message
...
Is anyone engaged is a design philosophy that seeks the design of VHF
yagi's
with the smallest acceptable diameter of elements?

What you are trying to do is to design lighweight VHF yagis, you are
seeking
how small you can go with element diameters before performance begins to
suffer.
The performance that suffers (afaik) from smaller antenna elements is a
small lowering of the 'bandwidth' of the antenna, and maybe a small change
in the 1:1 swr tuning point. Mind you I'm not an expert on Yagi antennas

I built, for a 'start from scratch' foxhunt, a 3 element yagi on 2m (~146
mhz) out of magnet wire glued onto a piece of poster board. I used standard
numbers and it worked fine. The hardest part was soldering wire thinner than
my hair to the coax and anchoring the coax to the poster board so it would
get pulled off.
I won the hunt over all the 'body shielded ht' guys, even taking 10min to
build my antenna...


Later that week I used it to call into a net on a local repeater, so it
handled 15 watts without anything melting.

Much more critical on a Yagi are element spacings (directivity and
Front:back ratios) and lengths (resonant frequency).

"Richard" wrote in message
...

"Tam/WB2TT" wrote in message
...

"Richard" wrote in message
...
Is anyone engaged is a design philosophy that seeks the design of VHF
yagi's
with the smallest acceptable diameter of elements?

What you are trying to do is to design lighweight VHF yagis, you are
seeking
how small you can go with element diameters before performance begins
to
suffer.

Richard,
I think if it is heavy enough to physically support itself, it will be
electrically OK. This turns out to be about 1/4 inch (6 mm) tubing at 50
MHz, and 1/8 inch (3mm) hard aluminum rod at 144 MHz and above.

Tam/WB2TT

Thanks. Of course over the years I'm used to seeing commercial TV and FM
antennas which tend to use 3/8" and greater for elements and because just
recently I've been comimg across designs using 4mm tubing it seems odd to
me. As if there's just got to be some big losses or compromises on using
say 4mm dia rod. But I now see that quite standard of course to use 3 and
4mm elements for high band VHFyagis. All is rather new to me. I should be
seeing 4mm rod as the norm for a VHFhigh band yagi.

Some of the variation in the size of tubing seems to depend on the quality
of the tubing used. Any ham antenna I have seen uses seamless fairly hard
alloy, whereas some TV antennas use a larger diameter rolled (if that is the
right term) tubing of very thin material.

Tam/WB2TT

In message , Tyas_MT
writes

I built, for a 'start from scratch' foxhunt, a 3 element yagi on 2m (~146
mhz) out of magnet wire glued onto a piece of poster board. I used standard
numbers and it worked fine. The hardest part was soldering wire thinner than
my hair to the coax and anchoring the coax to the poster board so it would
get pulled off.
I won the hunt over all the 'body shielded ht' guys, even taking 10min to
build my antenna...

This is interesting. I toyed with the idea of disposable antenna
systems for VHF Field Days. They only have to survive for 24hours, but
have to be big, cheap and light weight. I came up with the idea of
wrapping kitchen foil onto the thin dowel used to support plants to make
the elements (maybe plastic drinking straws would do on 70cm) and make
the boom out of bamboo or plastic tubing using string and a t-bar to
stop droop and sideways bend.

I never pursued it, but the card idea comes close to what I was
thinking of. Anyone tried something more ambitious. ?

Brian GM4DIJ
--
Brian Howie