Upgrading the QO-100 setup : 5 Turn Helix in a jar

After a few weeks I decided to setup the dish temporary in my backyard and made some cables to wire every thing up.. The original setup had a off focus placed 4.5 turn helix which was ok, but didn't give the expected  punch and  the signals where a little bit weak in SSB on the QO-100. Other operators told me that the signal was readable but not that strong.

So that was one thing to improve and the idea a of a new Helix feed was born.  

Jan covered the Helix with a 1250mL PET jar with a aluminium cover which perfectly protects the helix to the influences of the weather. So that idea I used in this 3D printed 5 turn helix holder  which can be placed over of the LNB lens  (my LNB has a 61 mm front lens), the holder can also be used with a 1000mL PET jar of the came company when used a 4 turn Helix.

I made the design publicly available for other hams to experiment with. If you have any comments, questions etc, please feel free to contact me through the contact form. 


Let's start building

To cut the large holes in the brass reflector I used 2 pieces of 20mm MDF  with in those the large holes for the LNB lens and the N style connector. The large hole was cut with variable large hole wood drill (see upper left corner green/white).

The sheet of 0.5mm brass is sandwiched between the sheets of MDF and a lot of holes where drilled in the brass and finally made to size and cleaned up with a file. (forgot to take pictures of the actual drilling and filing of the holes, sorry for that). 


After the large holes where drilled I used a sheet cutter to make the brass plate match the outer diameter from the 3D printed base. And made the holes in the jar lid using one of the MDF mold.


It seems to fit nice. 


And even on the LNB 


Added the Helix holder to it using 2 x M3-30 bolds. 


From a 2.5mm coper / steel welding rod I bend the 5 turn helix around a 25mm pole. The wilding rod is very strong and springy so when released fro the pole, it jumped back to a nice aprx 45 mm diameter helix. Extending the pace between the winding's made the diameter shrink to aprx 40mm inner diameter. Perfect for the Helix.

The matching plate is a triangle  cut out of brass as we used in the previous design. The I took is 72 x 17mm. 


The matching plate is bend into shape and soldered to the N style chassis connector and the Helix.  



 When everything was installed it was tweaking time, by bending the match more or less round (giving it more or less space above the ground plane) and placing the match higher and lower to the ground plane. . Using my NanoVNA V2 I matched it to 2400.250 GHz with a SWR of aprx 1.34:1 which is good enough for now.


Tweaking in the back garden. 


After the installation was done, I hooked up everything and got on the bird. Signals where almost 6 dB stronger then the pervious setup.

Remember, values below are lower because I'm working on the side of the band (not optimal bandpass)


SNR Right beacon : 29.3dB



SNR CW / Whistle in SSB : 29.2dB (0.1dB below beacon SNR)



SNR talking SSB : 22dB (7.3dB below beacon SNR)  Failed to get a screenshot SSB peaking 23.3dB. :-( 

But never the less, I'm very happy with the results.  

Note : when I make a QSO in the mid section of the band SSB peaks of 29db (avg 26dB).


Going /P 

Because I want to use the setup for /P operations, I modified the case with the AMSAT-DL upconv 6 in it with a water prove power connector so I there are no fixed cables anymore. Also the case got  a sticker on it with all the connectors described. I connected a 3dB 10W attenuator so i can have more control of the input power (the upconv can handle max 3W on SSB and 1W on CW) when using my Yaesu FT818. 



Adtional notes. 

When you have a 3D printer, check out this great design "QO-100 Ice Cone Feed" from Patric DC8PAT.