gamma match 70cm handheld
 

Hi,

Am trying a homemade 7 element handheld beam I'm making for 70cm
with .25" brass stock. Have a little junction box I have mounted on
the beam with a male socket so I can use a BNC cable for the radio
connection. Does it matter what size/type wire I use to connect the
socket to the brass element and the Gamma match element inside the
junction box? I want to use a socket so I can use different lengths of
cable as opposed to hardwiring the cable to the antenna.

Thanks loads,
Kurt

gamma match 70cm handheld
 

On Apr 4, 6:40 am, Kurt wrote:
Hi,

Am trying a homemade 7 element handheld beam I'm making for 70cm
with .25" brass stock. Have a little junction box I have mounted on
the beam with a male socket so I can use a BNC cable for the radio
connection. Does it matter what size/type wire I use to connect the
socket to the brass element and the Gamma match element inside the
junction box? I want to use a socket so I can use different lengths of
cable as opposed to hardwiring the cable to the antenna.

Thanks loads,
Kurt

I havent had good results using a gamma match on 70cm. Im not sure if
its something I am doing wrong or maybe everyone else has problems
with gamma matches on this band too. I have become a quagi fan for
this band.

Jimmie

gamma match 70cm handheld
 

JIMMIE wrote:
On Apr 4, 6:40 am, Kurt wrote:

Hi,

Am trying a homemade 7 element handheld beam I'm making for 70cm
with .25" brass stock. Have a little junction box I have mounted on
the beam with a male socket so I can use a BNC cable for the radio
connection. Does it matter what size/type wire I use to connect the
socket to the brass element and the Gamma match element inside the
junction box? I want to use a socket so I can use different lengths of
cable as opposed to hardwiring the cable to the antenna.

Thanks loads,
Kurt


I havent had good results using a gamma match on 70cm. Im not sure if
its something I am doing wrong or maybe everyone else has problems
with gamma matches on this band too. I have become a quagi fan for
this band.

Jimmie

Thanks

gamma match 70cm handheld
 

Kurt wrote in news:%FPQh.1209$zC.237
@newssvr22.news.prodigy.net:

Hi,

Am trying a homemade 7 element handheld beam I'm making for 70cm
with .25" brass stock. Have a little junction box I have mounted on
the beam with a male socket so I can use a BNC cable for the radio
connection. Does it matter what size/type wire I use to connect the
socket to the brass element and the Gamma match element inside the
junction box? I want to use a socket so I can use different lengths of
cable as opposed to hardwiring the cable to the antenna.


Kurt, if the connection is real short, it won't matter much and will be
compensated by the gamma trimming. Keep in mind that the diameter of the
gamma arm and spacing relative to the driven element itself are very
important, and to the extent your connection is an extension of that, it
will become important if it has appreciable length.

Gamma matches are very sensitive to dimensions around the gamma arm, so
they are not a very good match for an antenna that might get knocked
around.

Owen

gamma match 70cm handheld
 

"Kurt" wrote in message
. ..
Hi,

Am trying a homemade 7 element handheld beam I'm making for 70cm
with .25" brass stock. Have a little junction box I have mounted on
the beam with a male socket so I can use a BNC cable for the radio
connection. Does it matter what size/type wire I use to connect the
socket to the brass element and the Gamma match element inside the
junction box? I want to use a socket so I can use different lengths of
cable as opposed to hardwiring the cable to the antenna.


I read the other responses and have no quarrel with them. However,
I have seen a commercial uhf yagi with a gamma match. It was on
the side of a building and was probably cut for the 450 - 470 MHz
business band; it looked just a bit smaller than my 70 cm antennas.

My point: It can be done, assuming the antenna I saw wasn't a
total POS!

73
"Sal"
(KD6VKW)

gamma match 70cm handheld
 

Owen Duffy wrote:
[snip]
Gamma matches are very sensitive to dimensions around the gamma arm, so
they are not a very good match

Pun intended? ;^)

for an antenna that might get knocked
around.

Owen

I agree; rigidity of the matching section is all-important. But, I don't
think it'd be too hard to accomplish, using a chuck of plastic/teflon
block... the gamma rod would be only a couple of inches long.

Bryan WA7PRC

gamma match 70cm handheld
 

Hi,

I made the antenna out of a wood beam and 1/4" brass stock.
I used the QY4 program and the utilities program. Used some solid
18 gauge wire for the gamma match with a 4.7pf capacitor.
QY4 recommended 4.2pf. I used a small plastic box to house the
BNC connector, the gamma wire and the capacitor. Looks pretty
professional actually.
Well, I had set the program to optimize the antenna for 433Mhz
as that is what I was going to start with on my tracking transmitter.
Plugged the Yagi into my handheld, set the power to low, set the fwd
indication on my SWR meter and then did the ref reading. I was shocked
to see that it was 1:1.2. Set it up to 450Mhz and saw it was 1:1. For
this new ham, it was pretty surprising for a first project.
Will be using the antenna mainly to track an RDF beacon in an amateur
rocket. The link is here if your curious to see the unit. They make one
that transmits GPS data too. http://bigredbee.com/BeeLine.htm
Did some testing and I don't have as much directivity but I sure as
heck have plenty of gain with this setup. I might have to get a loop
if a model gets lost in some high weeds so I can get a better bearing
close-in.
I probably won't need an attenuator as I know the Foxhunt RDF folks
intentionally hide their transmitters in some weird places. Our rockets
most of the time land in an open area where our launchsite is.
Sometimes a high powered ship simply disappears off the pad and no one
sees it land. That's when the onboard RDF transmitter earns it's keep.
So far no one has lost a transmitter equipped rocket and there have
been several occasions where this has happened.
One person taped his transmitter to the shock cord that tethers the
pieces of the rocket under the parachute. He recovered his rocket,
brought it back and discovered no transmitter. They had been receiving a
signal all along but the model landed within sight. They went back out
into the field and found the still beeping transmitter with the loop
equipped receiver. Seems it was ripped off the shock cord and fell a
few thousand feet unharmed. This is where amateur rocketry can become
like an RDF foxhunt. :-)

Kurt


Sal M. Onella wrote:
"Kurt" wrote in message
. ..

Hi,

Am trying a homemade 7 element handheld beam I'm making for 70cm
with .25" brass stock. Have a little junction box I have mounted on
the beam with a male socket so I can use a BNC cable for the radio
connection. Does it matter what size/type wire I use to connect the
socket to the brass element and the Gamma match element inside the
junction box? I want to use a socket so I can use different lengths of
cable as opposed to hardwiring the cable to the antenna.



I read the other responses and have no quarrel with them. However,
I have seen a commercial uhf yagi with a gamma match. It was on
the side of a building and was probably cut for the 450 - 470 MHz
business band; it looked just a bit smaller than my 70 cm antennas.

My point: It can be done, assuming the antenna I saw wasn't a
total POS!

73
"Sal"
(KD6VKW)

gamma match 70cm handheld
 

Kurt wrote in news:3McSh.7893$YL5.5717
@newssvr29.news.prodigy.net:

....
Did some testing and I don't have as much directivity but I sure as
heck have plenty of gain with this setup. I might have to get a loop

Kurt,

Congratulations on your success.

Gain and directivity are related, Gain=Directivity/Loss, or in dB, Gain(dB)
=Directivity(dB)-Loss(dB).

So whilst it is possible to have gain without directivity (due to high
loss), the reverse doesn't happen.

Owen

gamma match 70cm handheld
 

Kurt wrote:

Well, I had set the program to optimize the antenna for 433Mhz
as that is what I was going to start with on my tracking transmitter.
Plugged the Yagi into my handheld, set the power to low, set the fwd
indication on my SWR meter and then did the ref reading. I was shocked
to see that it was 1:1.2. Set it up to 450Mhz and saw it was 1:1. For
this new ham, it was pretty surprising for a first project.

This is exactly why I never trusted gamma matches on 70 cm. I consistently
got nearly perfectly flat matches all the way across the band using a gamma
match. This usally something aint right. and the antenna is probably
radiating more in the infra-red region than at the desire frequency. No
doubt there are others more skilled than I who can make it work For me the
quagi has worked to damned well for me to bother.

Jimmie.

gamma match 70cm handheld
 

"Owen Duffy" wrote in message
...
Kurt wrote in news:3McSh.7893$YL5.5717
@newssvr29.news.prodigy.net:

...
Did some testing and I don't have as much directivity but I sure as
heck have plenty of gain with this setup. I might have to get a loop

Kurt,

Congratulations on your success.

Gain and directivity are related, Gain=Directivity/Loss, or in dB,
Gain(dB)
=Directivity(dB)-Loss(dB).

So whilst it is possible to have gain without directivity (due to high
loss), the reverse doesn't happen.

Owen

Hi Owen

I wonder if I misunderstand. I would think there could alot of
directivity in an antenna pattern but the system could have minimal gain due
to losses.

Jerry