OK1DFC 8m offset - feeds


432 MHz


Construction of the feed horn for the 432 MHz band continues. Today I made a box for LNA and relay. The work on the design of the feed, its placement in the feed point and rotation in V and H polarization is completed. Today I will install the feed into the dish and try how the unit works. If everything works as I hope, I will QRV in ARI EME contest on 432 and 1296 MHz bands




Finally I also got around to making a feed for the 432 MHz band. I chose the proven loop feed design described here and used a power relay to switch the RX and TX paths. Next, I used the miniature SMA isolation relay and VLNA described here. Now I need to align the ALU box with placement on a KR400 rotator to change polarization vertically and horizontally, with the ability to continuously adjust the angle of rotation.


1296 MHz


I originally wanted to participate in the DUBUS contest on 432 MHz, but because I had not finished the LNA and feed and because the EME expedition on KH6 was coming up, I decided to spend the nice weather to finish the work on the new offset dish. It was necessary to make a jig for precise alignment of the feed in the focus. I hadn't had time to do this in the autumn 2021, so I waited until the weather had calmed down a bit and I could work on the metal parts with my bare hands. The antenna with the feed installed "by eye" did somehow work, I had 14dB of sun noise, but it was still 7dB behind the assumption I should have had.

So I made a fixture that can be installed using simple mechanical cubes in the new and original centre of the dish so that the apex of this fixture, the "triangle", is exactly at the focus of the dish. By making the jig mechanically rigid, the optimum position could be found by varying the length by sliding the winding arms of the feed holder. Also, the tilt plane clearly shows how the tilt angle (36) of the feed should be set in offset. The pictures are in the photo and video gallery, including print screens of the connection with the new alignment of the feed in the focal point. After roughly aligning the feed, I measured the Sun's noise as a control. 21dB is already the value I expected to have. After the moonrise, I still measured its noise. A value of 0.8dB also indicates that everything is already on track. In the next few days I will still work on finalizing the details and minutiae of the feed installation. After fine adjustment next day I have 21,5dB Sun noise and 0,9dB Moon noise by SFU 120

After moonrise I tried a few connections. Everything worked great so I waited for the N1V expedition from Hawaii to show up. At 01:00 I tuned to 1296.052 and waited to see when it would appear. While the moon was still rubbing its belly in the Pacific, a signal appeared with a level of -17DB. I immediately started calling it and got a report immediately. As the moon got above the horizon, the signal got better and better. Later I decoded it -10 to -08DB. The signal on CW would put him at 539-559. I got -17 and the QSO was home. So #47 WAS and #121 DXCC were successful. Now I'll wait for his last "dispatch" day and try CW. Now to finish the feed and try 432 and 2320 MHz. Hopefully it will be successful too.


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Septum feed with collar W2IMU for offset F/D 0,457. VLNA G4DDK 0,2dB N/F and 36dB gain. Feed in feed point. So far I'm still 4dB short of the expected maximum Sun noise level, but the weather is not good for outdoor work and measurements. Today it is already snowing and we have 0C outside. I now need to accurately measure the focal point and place the feed in the correct position. Looks like I'll be busy enough for next spring again.
I finished production of septum feed with collar W2IMU for offset F/D 0,457. VLNA G4DDK 0,2dB N/F and 36dB gain. This weekend I will install the feed into the dish and test the antenna finally properly illuminated. It's just a shame that the sun is at a very low declination this time of year.
Today I brought the W2IMU copper collars for feedhorns in 2320 and 1296 MHz bands. Now I have to finish the feeds for F/D 0,457 and make measurements and final antenna calibration.
For the new offset antenna it is necessary to produce new W2IMU collars to the currently used feeds for 1296 and 2320 MHz bands. I first calculated the collar dimensions and then designed a square-circle transition for the actual implementation of the 1296 and 2320 MHz feeds. The material used was copper 0,6mm thick.

The lower images show the calculated values for the dish with F/D 0.457 and the upper copies of the DXF files for the laser burning machine.

I expect the final semi-finished products for feed production on November 2nd.