Hi Bjorn!

You should no go any lower than 12V for power.

Al less than 12V the PA final (IRF510) will not work well.

At that voltage you can expect peaks of 1.5A when transmitting and an average 0,18A when receiving at medium volume in a speaker.

I hope this answers your question,
--
Ion

VA3NOI

Doh !!? I used wrong AGC drawing.? Reposted.

--
Rob G4NQX

Just to remind everyone and anyone with a new kit.

The tab on the IRF510 is "hot" dc wise and should be isolated from ground. i.e. DO NOT short or bolt directly to a grounded case, heatsink, whatever !
--
Rob G4NQX

Hi all,

To add to the Tips n Mods pages I would like a table of voltages at various points in receive and transmit to be used as a guideline for people who are fault finding.

Is anyone who has a built working example willing to do such readings for me ?

You could contact me off group at tasmod at gmail dot com to discuss the readings required.

Why not mine ? Well mine is a converted Hendricks BitX20a much modified to work on 40m.
--
Rob G4NQX

开云体育

Hi John,

Did you measure the input power consumption for your different input voltages?

I am considering to deploy a node in a context where input power is scarce and am looking for a power-lean design.

By the way, what is the function of the diode in the gate circuit of the 2N7000?

?Never mind. I get it now.

73,

K7TFC

OK, lets try for some closure. When my raduino crapped out on me while trying the wrong wire to calibrate it. I picked it up to see if I had the right wire and a blip occurred with the display, and a pop in the speaker. After rebooting there was no display and just blinking on the nano and a tick in the speaker. When looking around I saw a bare black wire tip from the 8 pin connector near the heatsink facing me. The black wire doesn't explain the results, and the solution. But the PA must have been shorted and damaged, but not destroyed. I noticed the heatsink not getting as warm as before. Changing out the PA seems to have fixed that problem a bit. One thing I was doing wrong was not using a dummy load on the watt meter. Instead I was using a unmatched G5RV jr. connected to the meter. And connected to the bitx directly. What do smart radios do when you transmit into an unmatched or unbalanced antenna? They hold back full power. So, my testing is still not ideal, but better. I am not going to buy a faster multimeter just for this. So far this is the first time it has been inadequate for my needs. So, that's three times the final had to be replaced with my radios. The first one I over powered it with 13V, the second had the same type and It was just a bad sounding signal that got me an official observer post card. Replacing cleared it right up and it didn't get too hot anymore. This time with the bitx, the new PA sounds better and warms the heat sink, but not the dummy load. I would expect it too. It really gets very hot when I use it on my 6 and 7 watt cw transceivers. It is a 51ohm 5 watt resistor I put into a bnc connector with two wire terminals on one end. Like a dc power socket or plug. But different modes have different duty cycles. I imagine If it had cw, reading the power meter would be rather impressive.I can talk to most of the country with 20 watts. So to summarize, Don't think your raduino is dead yet. And keep the zombie raduino away from your heatsink.

So yea, change your parts when they are suspect. Cheap kits do have em all the time.

Now let the hacking begin!

There are two capacitors labeled "0.1". Just to be sure, does this mean 0.1 uF or 0.1 nF?

I think the convention is that all capacitor values are in ?F (that's microfarad in case the "mu" character doesn't show up on your screen) unless otherwise indicated.

I'm going to try this AGC in my BitX40. By the way, what is the function of the diode in the gate circuit of the 2N7000?

73,

Todd K7TFC

开云体育

If thinking about getting a scope, you could do far worse than investing a little time to read up on this blog

I bought a Tekway DST1102B back in 2011 and followed the instructions on the blog to get from 100 MHz to 200 MHz just by software change. I felt very pleased with myself until I later discovered that I could have achieved very similar results? by performing the software conversion on the still cheaper 60 MHz version.

Still, 7 years on, I'm happy with my scope.

Bill, VK7MX

开云体育

The 5.5nF and 3.3nF are standard values, .006 uF or 6nF and .003 or 3 nF are not standard valuesand would therefore be very hard to find, assuming some manufacurer actual makes them in those values.

Bill, VK7MX

I am ready to finish this thread. I plugged in the 20V adapter into the final and got 18 watts on the mfj-9213 qrp meter. ?I only took me three weeks to get to the starting point. The first hack will be "more punchy audio", and "auto gain control", then "CW" while working on the enclosure. I found a full sized shiny bare metal lunch box like the ones we had in the eighties.?

Or is the first Bitx 40 hack, getting it to work first?

Fortunately those hacks have been well documented. I won't have so many questions or delays anymore. Until I drop a metal screwdriver on the top of that SMD board.

Thanks everyone. Read ya later.