The AM Forum

Hi all,

New to AM fone, so this is my first post. I'd like to improve the  TX audio bandwidth on my 940. I'm getting reports of great modulation, but vastly reduced treble response - perhaps this is characteristic of the xtal filter on AM mode. One recommendation was to process my microphonium audio outboard with, say, a dBx 286 or a multi-band EQ, and try to "push through" the tight bandwidth of the filter. I reviewed Don KE1IZ's audio modifcation page here - http://www.amwindow.org/tech/htm/ts940s.htm - and got to thinking. If I were to install a switching TS jack and 1:1 audio transformer at the point he recommends, I could use external processing with a connected mic, and be able to use the rig in its stock configuration with the jack disconnected. I've also heard audio can be injected at the back into one of the phone patch RCA connectors - which means I wouldn't have to drill any holes. Thoughts of how I should go about this? Open to suggestions. I have a few pieces of AF processing gear in the arsenal.

Thanks!

-Patrick, KC1DPM

Hi Patrick and welcome to the forum!

I have worked a couple of guys who have done the power control FET modulation scheme (AKA RF Stage Modulation) with the TS-940 and they sounded beautiful. Plenty of clean full fidelity audio with very nice looking signals on the scope. You do have to take care to restrain the TX bandwidth as you are completely bypassing the TX filter with this method, but this can be handled pretty well by rolling off the audio with high pass cut-filters that are in audio voice processors like the RANE VP-12 and others. The DBX-286 might not be able to handle that task as well as other voice processors with its "HF Detail Enhancer" but you could always follow it with an EQ strip to cut things above 5K or 6K.

You might want to chat with Phil - W2PHL who has done the power control FET scheme on lots of different SSB type rigs. He might be able to point out any pitfalls that he might have encountered with various implementations.

Good luck!

Rob W1AEX 

Oops.  Lol.

--Shane
KD6VXI