Saturday, 11 November 2017

Vertical polarisation

Tried to work the DX7EME expedition in the beginning of the week but did not receive anything at all. Not even the slightest trace of them.
They TX circular polarisation but later discovered an error on one dipole which led to some sort of linear pol and the few stations receiving them that could alter their polarisation saw that they where stronger on vert pol.
So how to add vertical polarisations on the setup I have.
Try to rotate the entire stack is not doable and to setup an entire new vertical seems to much work.
The two possible sollutions I see is to add an array of vertical antennas on the booms I have today but in front of the vertical antenna mounting tubes or go large dish.
I did some calculations and a YBN 14 element yagi would fit in the front part of the present antennas.
The stacking distance will be larger the optimum creating sideloobes stronger but in my mind the easiest solution to the problem.
Would not interfere with the horisontal array even when I change to open wire feed as the stacking cables would be coaxial for the vertical array and "hidden" on the mechanical structure of the antennas.
I have allready decided I will rework the setup next summer with lowering the mast and adding open wire feeds instead of the present coaxial and I will also remake the plate where the triangular horisontal boom is assembled on as it seems as the weakest part at high winds.
This will require the array to be taken apart anywhay so why not in the process drill for vertical element too.

I was intended to try to optimize the amplifier tuning but did not find the time to do it this week but hopefully will find the time next week.
Had a nice chat with Toshi, JE2UFF the other day on the HB9Q chat and found and started reading his blog and they are designing a kW amplifier that looks really interresting.

Have had a problem with the preamp not starting when switching to RX and investigated that and it turned out that the Relcom RX / TX relay up in the array was occationally not making proper contact.
So I removed it and pulled it apart to clean it but discovered that the TX part was quite severely burned and RX part oxidated.
Bought this relay and the other I burned completely just before the 1st part of ARRL contest in october used from a ham in Sweden and starting to suspect that they was more or less burned allready when I got them.
Have never exceeeded the max power rating and the have seen very moderate use here so most likely something has happned in their past life.
Cleaned it up and it works ok at the moment but need to change before it brakes completely.
Have some Russian REW-14 that will handle the power but then I need to add an isolating relay for the preamp as they have less isolation then the Relcom I use now.
Have a box of old Sievers Labs relays too which are similar as the Relcom and has some 80dB of isolation on 432 MHz that could be used but I have no information of power handling capbillity so It could be a gamble to try.

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