Tuesday, 9 January 2018

Preamp and relay failures.

The weather since last update has been either rain or cold so no further antenna work has been done.
Tried to work some after new year but the preamp blowing and relay blowing is a constant issue.
Exchanged the preamp as said in last post but blew it after some 10 CQ´s again and built a new relay box containing a Russian REW14 relay as main relay and a Siverslabs as RX isolation and termination relay but blew that setup too including the preamp after some 10 CQ´s or so.
Have not yet removed it form the mast as the temperature has been to low but will do so as soon as it rises again.
So I am not 100% sure the relay broke but the VSWR is like 7 and no preamp.

The REW14 relay should withstand the power without any problem at all and my first thought was that the amp is oscillating or something strange as it does happen in the middle of a TX sequence and not while switching.
Tobbe SM7EOI had an idea that maybe the power inside the PA is causing the switch that controls the RX/TX relay and preamp to switch on occasionally due to high RF levels while transmitting and this could for sure explain the preamp and relay failures.
The switch is a P channel FET switch that is located within the PA enclosure so I will try to design a circuit that triggers on the control signal and transmit to see what is happening.
Or I will design a new system for controlling and switching completely.

Another thing I discovered was that when I blew the last relay the PA indicated high VSWR but did not shut it off.
It still continued to TX and I had to stop with the JT software.
This should not happen but still it did so I need to check that in the PQL controller circuit.
Believe I have experienced something similar on the 2m PA as well so maybe there is something needed to be reworked.

Besides from that we have had our share of the flue and now the work has started again.
Will try to find an isolated 30-40mm bar or tube so I can mount the dual pol yagi on an az/el rotor before the next high declination time which is in 2 weeks so I can monitor the difference in signals from the moon with dual pol.
I think I have a boom to make a second of these antennas but don´t think I will find the time to make that.
Could be interesting to see but I have some other things to attend to first.

Have had a discussion with John ZS6JON and he is planning to build a similar setups both for himself and a Ham colleague.
As the weather is like it is here in the winter time, my plan is to do the conversion of all my 8 antennas with vertical parts when the weather gets warmer and when I have planned to also lower the mast and change to open wire feeds.
So most likely he will bet me and manage this before as his weather is more favorable at the moment.
Looking forward to his work and information and will support them as much as I can.

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