New Sirio 1/2 wave Gain Master

[Riverman]

Have had this antenna almost two months now. Love it.
Pros:
Easy to assemble and tune.
Stiff. Very little bend/movement in high winds.
Rain has very little effect on SWR.
Bright red coil/choke eliminates any CMC.

Cons:
The 500 watt limit might be a problem for some. (Not for me.)

 

[hotrod]

Have had this antenna almost two months now. Love it.
Pros:
Easy to assemble and tune.
Stiff. Very little bend/movement in high winds.
Rain has very little effect on SWR.
Bright red coil/choke eliminates any CMC.

Cons:
The 500 watt limit might be a problem for some. (Not for me.)

the 500 watt power limit ..is that ssb or am carrier??

 

[Riverman]

the 500 watt power limit ..is that ssb or am carrier??

500 watts continuous.
Haven’t seen an SSB limit.

 

[snippits75]

Instructions said to set lengths of top two sections at 71.6” for 27.2 MHz. SWR was high at that length. Wound up using 69.5” for each, resulting in the following SWR’s:
1.2@CH1
1:1@ CH20
1:2@CH40

I understand setting the length of the sections. What I don't understand is why it says to trim the excess coax.

"Insert part 7 on cable until it stops." Does the cable go all the way through part 7, or does it have a stop? I am thinking the cable goes all the way through part 7, and then leave round about 1/2 inch play. Then trim the excess cable. Is this the correct way?

 

[Riverman]

If you extend the two loose sections so that each is 71.6” in length (per the instructions) there will be about 1/2” of the cable extending out the top. Attach the brass part with Allen screw and seat it in the end of the top piece. Place black cap on it and you are supposedly set for the middle of the CB band. That didn’t work for me. I had to carefully trim the cable a half inch or so at a time, put it back together, put it up and check SWR. I did this until I had the SWR lowest at ch 20. The final result was each of the two loose sections were 69.5” in length, leaving the trimmed cable sticking out the top 1/2” before attaching the brass piece and pushing it down into the tube.

Hope that makes sense.

 

[Riverman]

I understand setting the length of the sections. What I don't understand is why it says to trim the excess coax.

If the antenna (inner cable) is too long, the SWR will be higher on ch 40 than it is on 1. As you trim it, you are in effect shortening the antenna and shifting the point of lowest SWR. Most operators do this so that the lowest reading is at the middle of the band (ch 20) and fairly equal at the highest and lowest channels. In my case, the cable was too long and had to be trimmed. That may or may not be the case for you depending on your surroundings.

Maybe someone else can explain it better.

 

[snippits75]

Excellent explanation Riverman. I know exactly how to do it now. Thanks

 

[snippits75]

I ordered the Gainmaster half wave today. Will definitely guy it like Sirio suggests.

Going to go with the 71.6 inches(1820mm) sections, and hopefully it will be good. It will end up 24 feet above ground.

 

[Riverman]

I ordered the Gainmaster half wave today. Will definitely guy it like Sirio suggests.

Going to go with the 71.6 inches(1820mm) sections, and hopefully it will be good. It will end up 24 feet above ground.

The guying is definitely needed for the 5/8 wave version. I don’t use guy wires on my 1/2 wave. It‘s really stiff and bends very little, even in 50-55 mph winds.

 

[Marconi]

I ordered the Gainmaster half wave today. Will definitely guy it like Sirio suggests.

Going to go with the 71.6 inches(1820mm) sections, and hopefully it will be good. It will end up 24 feet above ground.

snippits75

Can you give me the frequency you cut the 2 wires for?

Can you give me the bottom wire dimensions (L" x D") (Length" x Diameter) for the bottom radiator wire?

The the inside diameter of the coil?

How many coils did you use for the choke.

The dimensions of the top wire element L" x D"?

What is the total overall length of the radiator from the bottom of the coil to the tip of the radiator?

73's and Thanks

 

[snippits75]

"L" (1820mm) is what the two sections are set at. Overall, the antenna should be just over 18 feet in length. The 24 feet is what it will be mounted above ground.

If I go by Sirio tuning directions with "L" at 1820mm, I should not have to trim the top end of the wire because 27.205 is the resonant frequency according to the SWR curve chart.

 

[Marconi]

snippits75,

Sorry 75, I've been laying on my back for several days and today I just got to feeling better today.

So, I thought I would try and get my GM 1/2 wave model working better. I saw your post with some of your dimensions, and I want to see if I could get all of your dimensions if you have not got it mounted by now.

I went into the hospital on January 4, 2023, and after 7 back and forth trips to the hospital, a COPD setback, pacemaker replacement surgery, Low Blood Pressure, and Brain Fog as a result of Mini-Strokes. I just can't remember currents events in my life.

Sorry again. I just wanted some dimensions for the GM 1/2 wave. That is OK though...by now you've likely already installed your new antenna.

 

[Marconi]

Please, does anyone have the 2 radiator wire diameters?

 

[snippits75]

Hello Marconi,

When I get the antenna, I will measure the diameter of the top and bottom of the wire/coax with digital caliper. The coaxial choke is inside a plastic cover, so I will measure the outside of the choke the best I can.

 

[Marconi]

Hello Marconi,

When I get the antenna, I will measure the diameter of the top and bottom of the wire/coax with digital caliper. The coaxial choke is inside a plastic cover, so I will measure the outside of the choke the best I can.

Thanks, my Friend.

73's