Wednesday, June 10, 2020

New 40m 4el full size yagi - part 2: elements

Some more work on antenna is done. Weather was crazy but made incredible pictures :) Antenna elements are assembled and all problems are fixed. Thanks to Jiri OK1RI for help with one tubing problem.

Pavel OK1MU relaxing on boom :)
 Original antenna by:

Wednesday, May 20, 2020

IC-7800 power supply failure

I use my Icom IC-7800 only for a few contests in a year and sometime for remote operation... About 2 weeks ago I was monitoring 6m and after 4 hours the radio died. Switched off 16A fuse... 
I take it at home and called to Karel OK1CF for help. Karel told me a lot of experiences from: how many screws I have to do, to how imposible is to find schematic diagram from it etc.
Thanks a lot Karel. 

True is, that the PS is black box from Futaba, code is FP2346C. Nothing on Google. The service manual from Icom is very nice, but there is nothing about PS :( 

I started opening TRX. Compare to IC-7600, Kenwoods etc, this is really different TRX. It is almost impossible to try anything when you remove some box. You have to disconnect a lot of flat cables, disconnect coaxes etc. 

I removed a few boxes and than power supply. First look and problem found. Both mosfets + resistors in the gates grilled... +15V part was dead.
I ordered new FETs but on 99 % also the driver should be dead. Replaced and yes, no signals to gates :( I tested rest parts of the power supplies (HV, +8V and +48V). By shorting optocoupler PC5 I switched on rest parts. Fan started, +8 and +48V too. Great some good news. Than I have decided to try last thing - apply external +15V. Connected PS to TRX and bingo, TRX alived! Not nice, but better than lost full TRX.
Icom needs now external +15V and about 4A.

 Died +15V PS part
 Disconnected HV (390V DC) and connected external +15V 


Sunday, May 17, 2020

New 40m 4el full size yagi - part 1: tower & boom

This is is the biggest antenna project after 4 x 6el H-frame for 10m. We have spoken about this 4 el 7MHz yagi for long years. Like: "one day..." And also due to the COVID-19 this project could start. 

We have to thanks a lot to Jiri OK1RI for many hours of simulations because this antenna has crazy tubing. The elements and also the boom are from the biggest Titanex log periodic antenna. The material is incredible, maybe impossible to buy it here in this time... Jiri helped us a lot not only with the design but also with all his life experiences. Thanks a lot Jiri!!!

Antenna will have 19m long boom. Elements start with 105mm tube and end with 11mm. It is 14 diameters of the tubes :) Elements are around 180kg and boom 140kg. So together around 320kg of this incredible aluminium material. Longest one is 23m. The boom is 70x70x70cm and as you can see, you can walk on it without any problems :)

Thanks a lot to Pavel OK1MU for all his work around it in the past as well as now, during the covid-19 restrictions. Pavel spent all his free time with it. Also thanks to Jarda OK1XUB, who helps him a lot.

There are some photos from last weeks.

Pavel OK1MU walks on th boom.

Martin OK1UGA works on 6m dish.