The ESSB modifications I have performed on the TS-940 have provided a very strong foundation for AM operation. I have received several positive comments on the quality of my AM transmissions.
The specific ESSB modification that I attribute to the high quality AM performance is the direct application of audio to the balanced modulator. Check out my TS-940 Mod page for details.
The bandwidth I was achieving with the stock 455K AM filter (CF2 on the IF board) was around 5KC. The audio fidelity was pretty good at this BW but I wanted more.
Though discussions with Bob, WB9ECK and Steve, KG8CQ I decided to install wider AM filter. Mouser Electronics has a great selection of Murata Signal Conditioning filters. I found a filter with the exact footprint required to interface with the 940 IF board.
I purchased several different bandwidth filters but ended up installing a +/- 7.5 kHz @ -6db (15 kHz max) filter. The mfg part number is: CFWLA455KEFA-B0.
The installation was very easy (if you are comfortable removing and soldering on the IF board). The photo below shows the bottom of the 940 with the IF board highlited in blue.
The photo below shows a close up of "CF2" on the 940 IF board. This is the filter you will need to replace.
This modification does not require any other adjustments to the rig... just remove the old filter and install the new one.
Please reference the audio recordings below to hear the before and after difference.
Recording made by Rick, VE6CQ of my the stock 455K filter
Recording made by W9AD 4/21/12 (he opened recieve filter from 6 to 10 kc during recording)
Recording of new filter made through a diode detector
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