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µBITX-V6 + AGC from kit-projects - loss of sensibility and very low "S" signal - #smeter #v6 #ubitxv6


 

Hello all !!!!

 

I finally installed the AGC kit-projects module in my µBITX-V6, carefully following all the assembly instructions, including taking the BF signal before the R70, using the 100 Ω resistor supplied with the kit, everything seems to work perfectly, only some small problems of very first impression:

 

1) The sensibility of the µBITX-V6 drops a bit, originally an antenna signal of -123 dBm was audible in the background with the volume at maximum, after inserting the module, even in the OFF position the minimum sensitivity dropped to about -90 / -100 dBm, this shows that the MOS in series with the antenna signal seems to be a bit too resistive even in the By-Pass position (AGC in OFF); the problem itself is not very important for QRP / portable rig use, but it could be a handicap if using the µBITX-V6 as a base station for "poor HAM", especially at higher frequencies.

 

2) The output signal "S" for use as "S-meter" is undoubtedly too low, the variation only goes from 0 mV to a maximum of 1.8 / 1.9 V with an antenna input of S 9 + 30dB (-43dBm in antenna), this severely limits the possibility of use through the A7 input without changing the ATmega328 Vf reference value.

 

3) It seems that "beats" appear in reception (it is only a first impression), probably generated by the NANO board and coupled between the cables of the wiring of the AGC module.

For the rest, everything works flawlessly!

 

Instrumentation used: HP8654B Generator + HP11710B Down Converter + HP8655A Synchronizer / Counter.

 

Anyone have ideas for how to improve the installation, especially in reference to loss of sensibility?

 

73 de IW4AJR Loris


George Griesbach
 

I installed my kit projects AGC board carefully in my v5 ubitx. My audio dropped appreciably in all settings
I did not take any readings, just my ears. So, I un-installed the AGC board and jumpered the cut trace and now my audio is still lower than before I made the mod.
SO I guess changing the audio ic is next and see if that helps.
73-George