Worldwide DX Amateur Radio Forums - Ham - CB - HF - VHF - UHF

Over the years I've heard many customers state that most HF rigs are not able to reproduce good sounding AM. My response has been to abandon the low level IF modulation technique in favor of low level RF modulation. Simply put, the IF stages of HF rigs have too many filters inline that restrict bandwidth. It is not worth trying to modify the IF stages. The modification found here The AM Window: Tech: Mods: TS-940S will make your TS-940S sound like a broadcast transmitter on AM and it also improves the SSB response.

And something else to keep in mind is that CB/ham radio is not 'broadcast' radio, there is no good excuse for some of the 'Hi-fi' audio you hear on the bands. Quite simply, all it produces is some 'brag' factor and interference. Take a good look at what you are calling 'good' audio.
- 'Doc

Believe me, A HI-FI or "broadcast quality" AM transmitter will cause alot less interference than a connex 3300 wit dar peak and tune! Problem with the TRUE Hi FI AM is that most recievers dont have a hi enough bandwidth to hear all of the transmitted signal.

It's important to understand that this modification accomplishes two things. The first is that it removes modulation from the balanced modulator and the IF stage. This alone has tremendous impact on the transmitters ability to reproduce positive audio peaks. This gives the ability to modulate the carrier at much higher levels before distortion occurs.

The second part of this modification deals with Hi-Fi. Changing various capacitors allows more bass and treble to pass through. This part has a lot to do with the microphone you use. If you don't want extreme bandwidth just use a D-104 or another communications style mic. If you want Hi-Fi then use a studio XLR type mic with some type of EQ.

I know most receivers will not reproduce the capabilities this modification allows. However, even the typical receiver bandwidth of 300 cycles to 3 KHz will definitely show a good deal of improvement with this modification. The TX bandwidth will only be as wide as the audio feeding the modulator. The radio is no longer the limiting factor, the mic is now, and can be tailored to suit your desires.

Why butcher a TS-940S when all you have to do is pick up a boat anchor and run REAL AM the way it was meant to be run? Hell even my old Heath DX-60 has superb audio and nothing has been done except changing the series coupling capacitors in the audio amp stage and using a decent studio microphone. Serious AM operators always use boat anchors or home brew plate modulated rigs.

__________________
Front/back ratio comes from the antenna. Forward gain comes from the wall socket.

EXACTLY !!!

- 399

Changing a few caps is hardly butchering. Look at the photos and then judge. Anyway the days of boat anchors ruling 75 meters AM are long past. There are more modified rice boxes, home brew class E rigs ,and flex radios on the band now then boat anchors. I've got a collection of them myself. I run a T-368 and a Johnson Valiant. They have great sounding AM but can not even come close to the positive modulation peaks and frequency response of the modified Kenwood. Did you forget about all the limitations dealing with modulation transformers in those rigs?

I've found that an extra 20 seconds in the microwave pops most of the kernels without burning

HiDef,
That is probably the best advice I've seen so far! LOL
- 'Doc

What limitations? I have seen plate modulated transmitters with flat freq response (within 1.5 dB) from 15 Hz up to 12 KHz and beyond. In fact I worked on some. They had names like RCA, Gates, Harris, Collins, and Continental. The only limiting factor about mod transformers is how strong your back is. Those SOB's are heavy!

__________________
Front/back ratio comes from the antenna. Forward gain comes from the wall socket.