Norbert went to the site this morning and turned the power down from 45W to 30W. This did not affect the received signal as we hoped.
For readers’ information, when a repeater is running from a single antenna the job of the cavities is to keep transmitter signal and noise out of the receiver. Too much power and the receiver is desensitised and does not perform properly.
We know that the cavities are working, we can feed signal into the receiver cavities from a signal generator and the receiver performs as it should. Norbert connected the new antenna system direct to the receiver cavities and it was very difficult to get a signal through. Remember system covers both the antenna and the coax.
This means there is a problem with the antenna system. As the antenna is new and the SWR is very low this means it is not likely to be the antenna (although possible). This leaves the coax. If coax is very lossy e.g. due to water ingress, then it will show a low SWR even though little TX power or received signal will get through. So our current theory is that we have faulty coax.
The coax is repurposed from an unused piece on the tower. It is certainly very old. So Norbert has taken home a piece of available LDF450 from the hut. He will put connectors on it and see if it has a low loss. If so it becomes a possible length for the antenna.
What next: Norbert plans a visit at the date/time he can get Dylan to help, perhaps about 2 weeks away (tentative 26/2/21) and weather permitting. He will climb the tower and with a power meter at the top he will check how much power is getting to the antenna. If it is very little he and Dylan will install replacement coax. While there he’ll check the SWR of the folded dipole as well. The tower does not have a ladder so climbing and staying in one spot can be very painful for the feet, legs and arms. This is not a simple thing we are asking of the antenna team.
In the meantime the transmitter is connected to the new antenna and the receiver is connected to the temporary antenna 12m up the tower. The transmitted signal will be weaker than we want and the receiver will not be as sensitive as we want, please be patient. The repeater team has made many visits to the site, we’re hanging in there. Hopefully you can too.