No signal at only high elevation

I have a question about the operation of the tracking Yagi antenna.

UHF communication is good at an elevation of about 10 to 40 degrees. However, even on the same path, we cannot receive any signals when the elevation is above about 40 degrees.

In Gomspace’s GS100, the ground station’s latitude, longitude, and altitude information is well entered, so the tracking function is fine based on the designated satellite TLE.
The doppler correction is also good.

Does anyone know about this issue?
Is there anything I’ve missed?

Best regards,

Hi, any more info on the system itself, how does the antennas look etc ?
Depending on the design of a yagi, they can be more or less wide band, tolerant of de tuning and obstructions on the sides or on the boom.
Distance from conducting objects (including coax) to the beam is approximately half it’s stacking distance, so try to keep it clear from all that.

Photos are attached.

Allright, that is a pretty nice setup (:
One issue is the close proximity of the dish edge to the second director, that will disturb the pattern and circularity for sure. That does not explain why it suddenly go deaf thou.
If you have a spectrum analyzer I would suggest to hook that up, and run it with preamps off and do a full 0-90 tilt, then with preamp on for another full tilt.
Look for strong signals and if it suddenly changes. At least 400-500MHz but would not hurt to look at 100 to 1500MHz as well. If it looks calm and no obvious signs of strong out of band signals then look at 430-440 or even narrower.
The reason for running with preamp on and off is to see if that one is saturated or intermodulated strongly so the signal of interest gets wiped out.
Even if there’s nothing up in the sky interfering, the antenna pattern isn’t perfect so could pick up something strong from the rear-/sidelobes.

Also take the mechanical part into account, it could be that due to mechanical stress when elevating connections are no longer making good a connection.

Agree regarding the cables and routing. Some prefer the winding method of having the cables go around the azimuth several turn to make it look like a clock spring. Personally I prefer to have a rigid arm holding the cables out from the rotator and hanging in a U-shape down to the preamps.
In the image below the altitude flexing is taken care of before collecting the coax/control from the rotator azimuth part and down to the preamps. Also making sure there is sufficient fixing of the cables as to avoid mechanical stress on the connectors.

Thank you for your comments. I’m going to check it out again.

Sounds like a bad cable/connector that disconnects when mechanically stressed. You can buy good quality cables at Pasternack.