Hi Al,
Good news! Just want to mention, the diode will drop 0.7V across it in this application. This is the reason the FET is used since it has a lower voltage drop across it.
This is will contribute to the lower current draw in Transmit (0.69 A). It's lower than what's usually seen.
Thanks for pointing that out. I'm aware of the voltage drop and this is a price I'm willing to pay at the moment, I compensate with a bit higher voltage if needed. :)
Do you have a way to measure transmit power out in Watts into a 50 Ohm (dummy) load? I'm just wondering if maybe one of the PA FETs (BS170's) is open and giving you the lower current reading. I don't want to be an alarmist, but it's something to consider.
I can estimated by measuring the peak voltage on the dummy, which is 13,89 V at input of 9 V (-0,7 V) and 7 A, so in the 3 W region I would guess.
When connecting an antenna the input voltage and current are different than with the dummy load.
I observed that my PSU changes voltage depending on the antenna, band and load ... maybe RF getting back in it.
For example when I set 8 V on 30 m while receiving, while sending the PSU goes to 9 V and the QDX draws 1,1A. On 80 m it goes from 8 V to 11,1 V and draws 0,77 A...
So now for every band I dial it in to have 9,7-10 V with load.
This seams to work reasonable well, WSPR goes over the Atlantic on multiple bands and I had some QSOs on 40, 30 and 20 m around Europe.
Maybe I need to decide on one band and build the 50 W amp. :D
Hi Wayde,
I use the following SWR bridge and tuning indicator with mine so that the max SWR 'shown' to the QDX will be 1:2... A fun and easy kit build and seems to work well as insurance for me!
That looks really nice!
I'm thinking about going the extra mile and building a full tuner like this ZM-4 ATU .
73 Alexander DM8TE
Alexander