Re: Transmitter Mods


Howard Fidel
 

I did not get good results with this mod, I found 80 meters had reduced output. It is also difficult to implement, since to remove some of the parts, you need to remove the FETs first to get to them, at least I would have had to do that.
I did another mod that was easy, and also helped, along the same idea as Ashar's. I put a small cap from the top of VR1 to the wiper. The value needed depends on where you set the pot. If the pot is set to the top end, then it won't help at all. The problem with all these transmitter mods is that we are pushing the parts to there limits, and when you design without margin, you don't get consistent results. This is kind of how we got in trouble with the original design to begin with, where the design compromises were made to keep the cost down. My original 3 part mod, which you did works fairly reliably. Allison is working on replacing the existing parts with new parts to improve the performance, which is great. I have taken a different track and am working on a new transmitter power train. The problem with that is you need a new PCB.


On 5/31/2018 6:49 AM, Rob Bleumer wrote:
Hi all,
I did the same mod as Nigel G4ZA did but using FT37-43 giving 30uH  in series with R86 
and 2 ceramic disk C's 220 pF.

And  al with exact the same power output results!!

Now I see another mod by Ashar Fahran  changing C81 to 470pF.in the new uBITX.

Could I do the mod by Ashar too and will this give a better result???
Who can advise me about this?
Rob PA0RBL


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