A 3.4GHz "Soup Can" feed

[VK3PY]

This is my just-completed 3.4GHz "soup can" feed for a 600mm dish. It is modelled on the design described by W5ZN in his article "Horns for the Holidays" which can be found at http://www.w5zn.org/files/Horns%20for%2 ... lidays.pdf

I can't recall what product my can originally contained, but it measures 66mm in diameter and is 102mm long. The probe dimensions and position are described in the original construction article. I dispensed with the tuning screw as it only seemed to make the matching worse. By carefully adjusting the probe length I achieved a return loss in excess of 40dB with the bare feed pointing into space. In front of the dish the RL is 28dB, which is still exceptional.

The coax patch cable leading from the feed to the dish hub is one of a bunch that I bought at local hamfests. It is labelled Suhner S 06162 D-2 50 Ohm. This one is 430mm long. I measured its insertion loss as 0.27dB at 3.4GHz. The right-angle Type-N adapter at the feed has negligible loss (I measured several of them and they each resulted in 0.03dB) and has no effect on RL.

Chas
VK3PY

[VK2ZRH]

Neat, Chas ! Well done.

Thanks for sharing.

[ZL1TPH]

I may have shown this before but I'm great believer in keep it simple like a Soup can or in my case a waveguide flange.
Of notes local hardware over here sell these fibre glass rod. So with a touch of glue solid and hopefully centred.

Flange feed 3.4 into 90 cm dish

[VK4CLG]

Nicely done. I like the white paint to match the dish. I did try a "soup Can" feed on 3.4Ghz a couple of years ago and was not too successful. I used a grid pack reflector but should give it another go on the 600mm dish. Did you have any issues with running the feed coax through the centre of the dish. I thought it might have had some impact on the reflecting surface of the dish.

Robert
VK4LHD

[VK3PY]

Thanks for your kind remarks, Robert.

Regarding the effects of the coax running back into the dish centre, it surely must have some effect, as would the support structure for the can. It is an inevitable consequence of this type of feed. I expect the main effect would be to introduce some uncontrolled side lobes in the radiation pattern. However, comparing the dimensions of the coax and support arm to say, a 10GHz waveguide feed (e.g. MITEC), I would think that the effects are minimal, considering the wavelength at 3.4GHz is about three times greater than at 10GHz.

A quick detailed description of the probe in my feed:

Referring to the photo below:

The spigot is 1.27mm diameter with PTFE dielectric, some of which has been removed so that it is flush with the inside of the can. The probe is made from the outer conductor of UT-085 coax which has been swaged down with coax crimpers to fit neatly over the connector spigot. It is 21mm long. A length of tinned copper wire is slipped into the end of the probe and soldered. This allows for easy adjustment of the over-all probe length. In this example, the tip adds a further 2.7mm to the probe length.

Chas
VK3PY

[VK2KYP]

Hi Chas thank you for showing us your "Soup Can" feed.

I am currently also make a feed for 3.4 GHz.

How did you remove the inner Dilectric and conductor from the UT-085 coax.

Thank you

73 Gary vk2kyp

[VK3PY]

How did you remove the inner Dilectric and conductor from the UT-085 coax.

Very easily. Take a piece of UT-085 and a sharp Stanley knife. Roll the blade over the copper outer jacket on the workbench, about 3-4mm in from one end. You only need to score it. Then use a pair of pliers to break off the end bit. Now pull the dielectric out with the pliers. It's Teflon, so it slips out quite easily.

Chas
VK3PY

[VK2KYP]

Thanks Chas, I use a mini-tube cutter to cut or strip the small hardline. It doss a very good job but can leave a "burr" on the cut edge which makes it difficult to remove the outer sheaf.

Thanks 73

Gary vk2kyp

[VK4REX]

Hi Gary

I drilled and tapped a piece of 1/8" (3mm) brass rod. The screw is a 1.5mm that has a locking nut to keep it in place. Gives you an easy adjustable feed.

Rex

[VK3PY]

Rex,

That is a neat solution. I contemplated the same approach, especially as my "soup can" already had a hole diametrically opposite the probe for a tuning screw (unnecessary as it turned out) which would have allowed "in situ" adjustment. However, I hit the sweet spot for the probe length with just a few iterations, so I quit while I was on a roll.

For those readers who are contemplating following your solution, could you publish the dimensions of your design?

Chas
VK3PY