SIRIO sy27-4 yagi keep the gama match or convert to hairpin , Thoughts ? experience ?

[Henry HPSD]

@ Brandon..Yes, you are good on track !
Some designs are a bit more forgiving when changing element diameter then others. Traditional "OWA" Yagis are rather forgiving. A good indicator would be the Q-factor of the antenna it self.
That also means the antenna will be less detuned due to snow/rain.
In genereal one could say..the lower the impedance of the Yagi the more critical (thus unstable) the design will be.

 

[DXman]

Henry gave me my measurements for my 5 element Maco beam several years ago using the gamma and I have been very happy the way it works.
The best part is - I don't have to have a amplifier to work DX around the world.

So just think how well your beam with do using the gamma match and if you are running just 200 watts!!
I know the gamma match is not the best but they will do just fine for 11 meters.

The "OWA" design that Henry mention is a very good design and many guys in the EU use them.

 

[Geoexplorer69]

Well hello everyone once again !
I have the new Sirio sy27-4 yagi antenna together and did I the first check today @ 5’ off the ground because there was too much wind to get it up the mast and I wanted to check the R,X and SWR .
I only had a piece of Rg58 20’ long to test it with as the lmr 400 hasn’t come in yet. Here’s my numbers checked with the nanovna
@ 27.385 the middle of the band and where I run lsb the most I have
1.1 swr, R=55 and X = 7
I did the test with and without an ugly balun 5-6 turns didn’t seem to make a difference X only dropped by 1 .

From 26.395- 27.800 I have pretty much the same numbers but the swr creeps up to1.2 higher starts about 27.700.

I still have the yagi on the ground and I want to know if someone can give me some advice on getting the reactance closer to 0 ?

Unless I’m missing something I think The numbers might change with the better coax although everything I’ve read suggests it might not make a huge difference.

Ok thanks everyone for your input and help
Cheers
Roger

 

[Crawdad]

Assuming your X= a positive (+) reactance, that means it is slightly inductive AT THAT FREQUENCY, i.e. slightly long. Personally, I'd take those numbers and run to the bank. Of course things will look different after it's in the air. Your ugly choke will have no effect on SWR or reactance values and may or may not prevent CMC on your feedline.

7 3

 

[Geoexplorer69]

Assuming your X= a positive (+) reactance, that means it is slightly inductive AT THAT FREQUENCY, i.e. slightly long. Personally, I'd take those numbers and run to the bank. Of course things will look different after it's in the air. Your ugly choke will have no effect on SWR or reactance values and may or may not prevent CMC on your feedline.

7 3

Thank you crawdad ‘
By slightly “long “ are you referring to boom length or fine tuning the “driven element “ ? It’s my understanding and please anyone correct me if I’m wrong that In Order to lower the reactance of X you change the length of driven element.

And if I do change the length of the driven element will that affect everything else negatively?

As for the CMC I have a number of ferrite beads that will handle the CMC . I’m using some on my current antenna which is a Sirio Monsoon 5/8 with ground plane &LMR 400 coax .

Thank you

 

[Crawdad]

Thank you crawdad ‘
By slightly “long “ are you referring to boom length or fine tuning the “driven element “ ? It’s my understanding and please anyone correct me if I’m wrong that In Order to lower the reactance of X you change the length of driven element.

And if I do change the length of the driven element will that affect everything else negatively?

As for the CMC I have a number of ferrite beads that will handle the CMC . I’m using some on my current antenna which is a Sirio Monsoon 5/8 with ground plane &LMR 400 coax .

Thank you

Sorry, I should have been more specific. You would adjust the length of the Driven Element to compensate for whatever type of reactance you're seeing, unless you are tuning with some type of matching device such as a Gamma or Beta (Hairpin).

Based on the numbers you posted earlier, IMO, you are good to go with an SWR of 1.1:1, a Z=55ohms and 7 ohms of reactance. If you could reduce the 7 ohms fine, but you or anyone hearing you will never notice the difference. Adjusting the length of the Driven Element slightly for tuning purposes will not affect the parasitic elements in any noticeable way.

Don't get super wrapped up in trying to reach perfection, even if you get there it will only be perfect on one frequency and it will definitely change a bit when you get it up in the air.

Good luck and enjoy,

7 3

 

[brandon7861]

Thats a darn good match and it will probably be different on the tower. You could try shortening the gamma rod by about 3% and lower the gamma capacitor by about 8% and see what that does.

 

[Geoexplorer69]

Sorry, I should have been more specific. You would adjust the length of the Driven Element to compensate for whatever type of reactance you're seeing, unless you are tuning with some type of matching device such as a Gamma or Beta (Hairpin).

Based on the numbers you posted earlier, IMO, you are good to go with an SWR of 1.1:1, a Z=55ohms and 7 ohms of reactance. If you could reduce the 7 ohms fine, but you or anyone hearing you will never notice the difference. Adjusting the length of the Driven Element slightly for tuning purposes will not affect the parasitic elements in any noticeable way.

Don't get super wrapped up in trying to reach perfection, even if you get there it will only be perfect on one frequency and it will definitely change a bit when you get it up in the air.

Good luck and enjoy,

7 3

Thank you crawdad ‘
I think I’ll just leave it and recheck everything when the lmr 400 coax gets here
Then run it up the pole and see if anything changes. I hope not but if I have to bring it down and fine tune .
Cheers

 

[Geoexplorer69]

Thats a darn good match and it will probably be different on the tower. You could try shortening the gamma rod by about 3% and lower the gamma capacitor by about 8% and see what that does.

Thanks Brandon 7861 ,
I’m going to recheck everything when the new coax gets here tomorrow, if everything goes well I’ll hoist it up and check it again. If I have to bring it down I’ll certainly give your suggestions a try .
I have to admit that everyone telling me to just get it up and talk has me thinking maybe I should be happy with what I have now .

My only concern is having things change a lot due to the fact I tuned it up with a 20’ piece of rg58 as that’s all I had on hand until I get the lmr 400 in tomorrow.

I do appreciate your input and used my nanovna H to take the measurements and rechecked everything with my MFJ 258B . I was surprised that the jived .

Ok thanks again
Cheers
Roger

 

[brandon7861]

Thanks Brandon 7861 ,
I’m going to recheck everything when the new coax gets here tomorrow, if everything goes well I’ll hoist it up and check it again. If I have to bring it down I’ll certainly give your suggestions a try .
I have to admit that everyone telling me to just get it up and talk has me thinking maybe I should be happy with what I have now .

My only concern is having things change a lot due to the fact I tuned it up with a 20’ piece of rg58 as that’s all I had on hand until I get the lmr 400 in tomorrow.

I do appreciate your input and used my nanovna H to take the measurements and rechecked everything with my MFJ 258B . I was surprised that the jived .

Ok thanks again
Cheers
Roger

Don't worry, it shouldn't change with coax length at all. The R and X will, but SWR will not (aside from being a little lower due to additional loss from longer coax).
I agree, put it up and start shooting some DX. An SWR of 1.2 is really good (99.2% of power making it into the antenna). Chasing perfection here will only keep you off the air. When you put it up, if it is under 1.5, don't bother taking it back down. Nobody will hear the difference.

As SWR goes up, you risk blowing your finals long before anyone would notice the difference, so as long as your finals are happy (<2:1), run it.

 

[Geoexplorer69]

Don't worry, it shouldn't change with coax length at all. The R and X will, but SWR will not (aside from being a little lower due to additional loss from longer coax).
I agree, put it up and start shooting some DX. An SWR of 1.2 is really good (99.2% of power making it into the antenna). Chasing perfection here will only keep you off the air. When you put it up, if it is under 1.5, don't bother taking it back down. Nobody will hear the difference.

As SWR goes up, you risk blowing your finals long before anyone would notice the difference, so as long as your finals are happy (<2:1), run it.

Yep , she;s going up tomorrow as soon as the new LMR 400u gets here and I do a re check on the numbers . I was really surprised by the low SWR from 26.975 to 27.700 with only the swr changing from 1.1-1 to 1.2-1 nothing else changed . Guess I still have a lot to learn.

Anyway I’m going to shoot for anything from 1.2 -1 and lower and if the X &R stay in the same ballpark the yagi is getting mounted , the skip has been rolling in pretty good and I want to shoot some serious DX .
Cheers
Roger

 

[Henry HPSD]

Good to hear you almost have it up and running.
If im correct, you tested the antenna horizontal 5 feet from the ground.
Beeing close to the ground the SWR will have some inlfuence on SWR.

The advice would be to tune the antenna for roughly 55 Ohms J 0 .
If the antenna goes up the impedance will slightly drop a bit..

Your have provided two different SWR indications.
26.395- 27.7 and 26.935-27.7 with values of 1.1 to 1.2.
If i set the antenna at 5 feet from the ground and match it.
And look at the 800 KHz bandwidth i too get the mentioned values.
Im seeing 1 to 1.21...1.23 so that looks like you are "in the spot".



Kind regards,

Henry

 

[Geoexplorer69]

Thank you Henry ,
You are correct. The numbers you have are pretty much what I had . I set the middle freq @ 27.385mhz . My SWR only started to climb up to 1.2-1 at the higher freq;s .

I’m sure there will be some more “tweaking “ and I’ve already resolved to the fact I’ll be bringing the yagi down a time or two so with that in mind I’m not going to be mounting the rotor until everything is set as far as swr, X&R ect .

One last question for you , since the ugly balun I made using 5 and then 6 . 4” loops only dropped the X down from 7-6 , What are your thoughts on using the ugly balun? I’ve read that it actually makes a difference in the way the yagi’s signal is transmitted properly.
Cheers
Roger

 

[Henry HPSD]

If you were to ask about an RF choke somewhere on social media ...you will have loads of people telling you :
Not needed, never used one etc, and perhaps some will tell you ... Yes..it does makes a difference.
It will also be one of those posts with a hundered replies where true knowledge certainly wont get the most thumbs up.

The fact is... it often does make a difference... but those differences are not always observed by the user.

Say...we have a dipole (2x quater wave) as in your Yagi... and we have a coax length which happens to be around a quarter wave length long...
Just ask yourself... how does the "RF Signal" know... it needs to go on the dipole and not on the outside of the coax ? Both are a quater wave long ...both will conduct..RF will go the path of least resistance...so without a doubt the coax becomes part of the antenna..

That (worst case scenario) will look something like this :

Now if we choke that current... we will get something like this:


So without "blocking" that path you could end up with the same amout of current that is on the element will also be on the coax cable...and that can cause issues. Unless you make sure there isnt a path ...it is decoupled.

I wrote a short story about the RF choke here:

RF-Choke – 19DX348 CB Antennas

cb-antennas.com

In short..
Will the antenna work without it ? ... well in many cases ..yes..(though there are worst case situations where performance will seriously lack...)
Will you notice it ?...well... maybe...depends on the situation...and on your skills to observe it (measure).
Should you use one ? ...without a doubt..yes...it is wise to do so !

Kind regards,

Henry

 

[brandon7861]

If you were to ask about an RF choke somewhere on social media ...you will have loads of people telling you :
Not needed, never used one etc, and perhaps some will tell you ... Yes..it does makes a difference.
It will also be one of those posts with a hundered replies where true knowledge certainly wont get the most thumbs up.

There is nothing wrong with taking precautions, use a choke/balun if you have one.

That said, I have made several VHF and UHF antennas and feel like I can speak to this. At those frequencies, CMC always shows up in the tuning process as a variation in the complex impedance when moving the VNA's test cable around, or running your hand along it. This really shows when working at 100-500MHz because of the shorter wavelength.

With gamma matching yagis, I have not experienced this problem. Of the 15 or so VHF/UHF yagis I have built and tuned, those with gammas did not appear to respond to changes mentioned above that would affect CMCs. This was the whole reason I dove into understanding the math of gammas, I liked them that much. I will never bother putting a balun on a gamma match unless I see evidence of CMCs.

If you believe you have a CMC issue at HF, changing the length of the coax without moving the antenna will cause a change in measurement since the CMC path is part of the antenna. If you can extend your coax roughly an odd quarter wave multiple (like a 9 foot truck coax with a barrel connector) and your SWR doesn't change, you don't have CMC's. It is easy enough to find out, so there is no need to guess or waste time/money on something you are not sure is even a problem.