Författare: Lars Thunberg

Satellite antennas tracking Greencube – May 2023.

Test of VHF/UHF Moxon antenna for my SatNOGS station. Read more here: https://community.libre.space/t/test-of-new-antenna-for-station-858-sm0tgu/10131

Step by step for changing the mainboard of a Rot2Prog rotor controller. Time aprox. 20 minutes.

First of all – remember to point your antenna to Azi = 0 degree and Ele = o degree! If anything goes wrong you know 100% where your antenna is pointing.

Remove the top cover and then the old mainboard (see red markings)

Carefully move the PROM from the old mainboard to the new one

Lift up the old mainboard

Lift up the cables marked in red from the old mainboard in place it at the same location on the new mainboard

Place the new mainboard in the metal enclosure and align in so all the push buttons on the front is working. Tighten the board screws and then mount the top cover.

Done!

With this online tool you can see elevation profile. It shows that it is impossible for me to work low elevation sat passes to my east: https://randymajors.org/elevation-on-google-maps

Let’s look at this SatNOGS observation of LUSAT that has a strong carrier downlink. It is not possible for me to receive to the East:

Compared to a West pass:

When my End Fed Half Wave antenna wire broke I decided to try a new type of HF antenna. I google and many seen happy with the Skyloop (or Deltaloop) antenna so I decided to try that type. I will not go into detail about this antenna, there are tons of articles on Internet – just google and read. My primary source of info for my constructions is from this page at HF-Kits.

Wire and support

I used this type of ”robot lawn mower perimeter wire” – it seems to be a good cable for use as antenna wire.

My garden can fit a 80 meter loop, so in the spring 2022 I started to get two wire support point as high up I could throw in two trees:

At the corner of the house I needed two more support points:

This is the actual shape of the loop:

First installation – with Choke balun

For RF choke at the loop feedpoint I made a Guanella Choke:

The antenna feedpoint is as below. You can also see the MFJ RT-100 remote antenna tuner I’m using. This is needed as the loop only has 50 ohm at 3.5 MHz and 7 MHz without use of 2:1 balun (see the SWR charts below). I’m not sure about the exact length of the wire for the loop, around 84 meter.

It was not possible to tune the WARC bands with this setup so in the next installation I used a 2:1 balun.

Second installation – with 2:1 balun and no Choke

In order to be able to work the WARC band (with my MFJ tuner) I decided to try a 2:1 balun. Balun design can be found at many sites but I used this one:

And in the box:

I skipped the Choke balun this time to see if it should work anyway as I’m only working max 10 watts. I can not see any RF problems without the RF Choke. Below in the SWR graphs you can see the result.

SWR measurements

At antenna feedpoint, without Choke balun. I didn’t need to cut the antenna wire much to get a good match. Strange to see the good SWR at 3.5 and 7 MHz, as the loop has 100 ohm impedance.

Next, with first version of 2:1 balun, antenna has the same length. You can see the much better SWR but the antenna is tuned a little low in frequency. At 3.5 MHz the SWR is now higher but better at all other frequency.

Below is the result after the balun is mounted in enclosure and antenna wire is cut/tuned a little. It is very good for 40m, 20m, 15m band and OK for 10m low end of band. 80m and WARC bands can be tuned with the remote tuner, that was not possible before without balun.

With this setup, the loop antenna can be used without tuner on several bands if needed.

Results and performance

I’m very happy with the result of this antenna! I have not been able to compare with my End Fed Half Wave (EFHW) antenna, so I can not back up my ”feelings” of the antenna result with actual numbers and facts. What I see when running FT8 and looking at PskReporter is:

• My signal is heard at the same distance as I can receive, that was not possible with the EFHW antenna.
• Received and sent signal reports are more equal now compared to the EFHW antenna.

I you have space for this antenna I highly recommend it. A 7 MHz version is just half the size of the 3.5 MHz version. It can be a little tricky to set up as four (or three for Delta Loop) support points are needed. Also, I recommend to use a 2:1 balun. In my case, the Choke balun was not needed.

Some initial results from PskReporter FT8 and WSPR with the second version with balun: