3.4G feed horn dimensions ?


Nick Gregory G0HIK
 

The 9cm's SG-Labs arrived yesterday and I'm cant wait to get going.

I've found on the G3PHO site a "Soup Tin" feed horn.

I've copied it and the SWR is in the green straight away :)

But what length should I make the waveguide section, it is not mentioned in the article ?

And what does a Chaparral horn actually do ?

Nick G0HIK
 







John Fell
 

Nick,
The standard tin length is good enough - the probe point to the end short of the waveguide ( Tin can) is more important .
No doubt Peter's data will be fine .
The Chaparral flange addition is to enforce a better distribution  illumination of the dish surface for higher F/d ratio .

The open ended can without any flange addition will work fine with a near prime (0.25 F/d ratio ) reflector , which requires near to 90 degree feed angle .

An alternative , easier to make , flange is a Super VE4MA .This works well with dishes in  the 0.55 to 0.8F/d range , such as the majority of domestic  Sat dishes .It is also possible to adjust the flange position although the data given on the W1GHZ website is close enough to fix the position .

73/Seasons Greetings 

John
G0API

On Sun, 6 Dec 2020 at 14:34, Nick Gregory G0HIK via groups.io <nickg0hik=googlemail.com@groups.io> wrote:
The 9cm's SG-Labs arrived yesterday and I'm cant wait to get going.

I've found on the G3PHO site a "Soup Tin" feed horn.

I've copied it and the SWR is in the green straight away :)

But what length should I make the waveguide section, it is not mentioned in the article ?

And what does a Chaparral horn actually do ?

Nick G0HIK
 







Nick Gregory G0HIK
 

Thanks John,

That is just the simple to understand information I needed.

I'll try it with just the open ended can first then.

Nick G0HIK


militaryoperator
 


Mine Nick. 


Ben G4BXD.




Subject: [UKMicrowaves] 3.4G feed horn dimensions ?
The 9cm's SG-Labs arrived yesterday and I'm cant wait to get going.
I've found on the G3PHO site a "Soup Tin" feed horn.
I've copied it and the SWR is in the green straight away :)
But what length should I make the waveguide section, it is not mentioned in the article ?
And what does a Chaparral horn actually do ?
Nick G0HIK


 





Neil Smith G4DBN
 

A simple round horn has a wide pattern and large side/back lobes, so it doesn't illuminate a shallow dish very effectively. That means the horn is probably seeing hot ground, as well as lowering the efficiency of the dish/feed system.

Fitting a choke ring or rings suppresses the sidelobes and helps narrow the pattern somewhat. 

The section of guide ahead of the probe helps to ensure that higher modes are suppressed and that the wavefronts coming out of the tube are pretty much planar so you will get an in-phase reflection across the whole of the dish. Rule of thumb is at least half a waveguide wavelength between the probe and the open end, but you can model it in OpenEMS or something to be sure.

The VE4MA style chokes are much simpler to make (and smaller) than a Chaparral, and you can adjust the width, depth and offset from the open end of the tube to fine-tune the pattern and sidelobe suppression.  W1GHZ's site has a lot of analysis of how to match the choke topology to your dish f/d. On a prime-focus dish, you have to take into account the extra blockage caused by the choke. http://www.w1ghz.org/antbook/chap6-3.pdf and there are good articles in DUBUS.

Without a choke ring, if your dish has an f/d of less than 0.4, you won't lose much on transmit, but you might have a little extra noise on receive. If you are using an offset with f/.d 0.6-0.8 then it is probably worth fitting a choke. It won't make any noticeable difference to the match.

A VE4MA choke ring looks like this, although I usually TIG-weld the rings to the horn - this one needed to be removable for fitting:

Fitting a scalar choke like this one (similar to the Chaparral in concept, providing a high-impedance surface of 1/4-wave (ish) slots) does clean up the pattern very well, but the blockage is too high for a small PF dish under 1.5 m or a 1.2 m offset

Neil G4DBN

On 06/12/2020 14:34, Nick Gregory G0HIK via groups.io wrote:
The 9cm's SG-Labs arrived yesterday and I'm cant wait to get going.

I've found on the G3PHO site a "Soup Tin" feed horn.

I've copied it and the SWR is in the green straight away :)

But what length should I make the waveguide section, it is not mentioned in the article ?

And what does a Chaparral horn actually do ?

Nick G0HIK
 






-- 
Neil
http://g4dbn.uk


Nick Gregory G0HIK
 

Nice Ben,

What is the diameter of your horn? And what function does the flare serve.

If I get this working, I'll be asking you for a sked soon :)

Nick G0HIK


Colin Ranson
 

uW’ers

 

Where does one acquire on of these white Chapparral thingys ?

 

Colin de G8LBS  ..... ....pondering different antennas for 9cm.

 

Sent from Mail for Windows 10

 

From: John Fell
Sent: 06 December 2020 15:02
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] 3.4G feed horn dimensions ?

 

Nick,

The standard tin length is good enough - the probe point to the end short of the waveguide ( Tin can) is more important .

No doubt Peter's data will be fine .

The Chaparral flange addition is to enforce a better distribution  illumination of the dish surface for higher F/d ratio .

 

The open ended can without any flange addition will work fine with a near prime (0.25 F/d ratio ) reflector , which requires near to 90 degree feed angle .

 

An alternative , easier to make , flange is a Super VE4MA .This works well with dishes in  the 0.55 to 0.8F/d range , such as the majority of domestic  Sat dishes .It is also possible to adjust the flange position although the data given on the W1GHZ website is close enough to fix the position .

 

73/Seasons Greetings 

 

John

G0API

 

On Sun, 6 Dec 2020 at 14:34, Nick Gregory G0HIK via groups.io <nickg0hik=googlemail.com@groups.io> wrote:

The 9cm's SG-Labs arrived yesterday and I'm cant wait to get going.

I've found on the G3PHO site a "Soup Tin" feed horn.

I've copied it and the SWR is in the green straight away :)

But what length should I make the waveguide section, it is not mentioned in the article ?

And what does a Chaparral horn actually do ?

Nick G0HIK
 






 


Eddie G0EHV
 

Try eBay, “c band LNB”

Regards,
Eddie 
G0EHV 

Launched into the ether from my iPad 

On 6 Dec 2020, at 18:56, Colin Ranson <g8lbs@...> wrote:

uW’ers

 

Where does one acquire on of these white Chapparral thingys ?

 

Colin de G8LBS  ..... ....pondering different antennas for 9cm.

 

Sent from Mail for Windows 10

 

From: John Fell
Sent: 06 December 2020 15:02
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] 3.4G feed horn dimensions ?

 

Nick,

The standard tin length is good enough - the probe point to the end short of the waveguide ( Tin can) is more important .

No doubt Peter's data will be fine .

The Chaparral flange addition is to enforce a better distribution  illumination of the dish surface for higher F/d ratio .

 

The open ended can without any flange addition will work fine with a near prime (0.25 F/d ratio ) reflector , which requires near to 90 degree feed angle .

 

An alternative , easier to make , flange is a Super VE4MA .This works well with dishes in  the 0.55 to 0.8F/d range , such as the majority of domestic  Sat dishes .It is also possible to adjust the flange position although the data given on the W1GHZ website is close enough to fix the position .

 

73/Seasons Greetings 

 

John

G0API

 

On Sun, 6 Dec 2020 at 14:34, Nick Gregory G0HIK via groups.io <nickg0hik=googlemail.com@groups.io> wrote:

The 9cm's SG-Labs arrived yesterday and I'm cant wait to get going.

I've found on the G3PHO site a "Soup Tin" feed horn.

I've copied it and the SWR is in the green straight away :)

But what length should I make the waveguide section, it is not mentioned in the article ?

And what does a Chaparral horn actually do ?

Nick G0HIK
 






<IMG_20201206_141909475.jpg><IMG_20201206_141924969.jpg>

 


militaryoperator
 

uW’ers
 
Where does one acquire on of these white Chapparral thingys ?
 
Colin de G8LBS  ..... ....pondering different antennas for 9cm.


I got mine here:  113332867052


Ben


Nick Gregory G0HIK
 

Me also Ben,

Where do you get the copper tube from?

Nick G0HIK


Nick Gregory G0HIK
 

Once again, Thanks for the great info Neil.

Tried with GD1MIP a couple of times today, no joy yet. But I'm going to a 2000ft location tomorrow for another try, fingers crossed.

Nick G0HIK


militaryoperator
 


ebay:  
192858456314



Subject: Re: [UKMicrowaves] 3.4G feed horn dimensions ?

Me also Ben,

Where do you get the copper tube from?

Nick G0HIK


Nick Gregory G0HIK
 

On Sun, Dec 6, 2020 at 08:57 PM, militaryoperator wrote:
192858456314
Thanks Ben


Andy GD1MIP
 

3rd time lucky and today we did it. A real 5/9 SSB contact.

G0HIK/P to GD1MIP/P.

About 45 miles across the sea. 

Andy GD1MIP