Re: ND6T AGC implementation for uBIT-X

Mike Woods


The modified T/R click fix from VA7AT (see link below) is probably a better one to implement ( ND6T uses an earlier VA7AT design, which is not perfect, and hence the subsequent mod by VA7AT).


On 29/04/18 1:45 PM, Kees T wrote:
I've been looking at the ND6T website and find several interesting, useful, and focused on minimalist circuits. 

1) The AGC circuit which we're discussing here. I have a board layout which is 980mils x 980mills and it seems to fit nicely. It offers jumper selection of 4 Hold times and AGC OFF......using 0 ohms for AGC OFF, "a" ohms, "b" ohms, "c" ohms, "d" ohms. It's a 2 sided board which you can attach with double sided tape to the back of an RF gain pot (5K) or wherever you want. The reason for mentioning the RF gain pot is that it's a recommended good idea and you wire it to the uBITX board using small coax. This is also explained by ND6T in the "Adding an RF Gain Control to the uBITX".

2) T/R Click Fix is a board half the size of the AGC board and contains the circuit defined by ND6T. I refer you to his write-up for implementation. 

3) The Polite Antenna Tuner also caught my eye and has a really simple minimalist technique using a broadband noise generator to tune the antenna and listen with your receiver for a null (when you are matched to 50 ohms). Seems to fall right in line with QRP rigs and tuners. And you don't require transmitting to get "close". Believe you me, a high BITX antenna SWR will take out an IRF510 in a heartbeat .....not so much for a RD16HHF1 RF MOSFET. Sounds like another ~ 1 sqin board. 

73 Kees K5BCQ

Mike Woods

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