Kenwood TS-930S

[Edward Cain]

Hello group,
   I just acquired this radio and am wondering if anyone in the group has any experience with AM operation with this transceiver.
   I am particularly interested in any documented mods for optimizing AM transmit or receive.
   FWIW, this radio is a 5xxxxxx serial # and has factory installed antenna tuner.

   I am aware of the power transformer issues and limited capability of the tuner.

   Any advice will be greatly appreciated.

Thanks,
Ed/KJ4JST

[k7iou]

Ed, the rig is capable of 25W of carrier in AM mode. If you see your power meter move upwards on voice modulation you are good to go. My Icom 756 would move rearward due to the ALC folding back power in AM mode. I had to build a circuit and plug it into the ALC with -1.6V to fool it so now I have forward modulation in AM.
Kenwood doesn't seem to have this design issue.
Enjoy!
de k7iou

[K1JJ]

If you have the skills, then build this balanced modulator board and install it into the 930.  It will give you DC to light clean audio frequency response with no undesired ALC action.  Bypass the TX AM filter as mentioned below.

http://amfone.net/Amforum/index.php?topic=32949.0

Match the proper I.F. and you're golden.


As an alternative, inject your hi-fi audio directly into the existing 930 balanced modulator and then disconnect or turn down the ALC pot until there's no ALC meter action on AM transmit.

For receive, tap the audio directly off the detector area and go into an small sudio amp and large speaker..   For RX filtering, a cheap and dirty method is to place a small 15 pF capacitor (or whatever works well) across the existing AM filter. Find a value that just broadens out the response, but not too much.

Tom, K1JJ

[k7iou]

If you have the skills, then build this balanced modulator board and install it into the 930.  It will give you DC to light clean audio frequency response with no undesired ALC action.  Bypass the TX AM filter as mentioned below.

http://amfone.net/Amforum/index.php?topic=32949.0

Match the proper I.F. and you're golden.


As an alternative, inject your hi-fi audio directly into the existing 930 balanced modulator and then disconnect or turn down the ALC pot until there's no ALC meter action on AM transmit.

For receive, tap the audio directly off the detector area and go into an small sudio amp and large speaker..   For RX filtering, a cheap and dirty method is to place a small 15 pF capacitor (or whatever works well) across the existing AM filter. Find a value that just broadens out the response, but not too much.

Tom, K1JJ

Tom, correct me if I am wrong the article you referred to is for Yaesu. Most or all hams I talk with on AM with Kenwood work well out of the box with no modifications. They won't modulate like a Valiant or Five Hundred but they do work good for a rice box and better than my Icom. 73 de k7iou

[Pete, WA2CWA]

Here's a quote off N2CKH's web site:
"For instance, the TS-930S I bought in the early 80's new, it has the optional AM filter for receive, but on transmit it is USB and full carrier. If you adjust it accroding to the owners manual it has no audio level (60% modulation ?) and the carrier falls back with modulation. I if you overcome the carrier with too much audio you will sound like SSB to all using AM receivers to hear your transmission. However, if you adjust the carrier level to about 10 watts or less then with modulation you will get a nice 100% plus modulated signal with a nice upward swing. You need to be careful not to overmodulate or you will sound like an SSB signal."

[K1JJ]

Tom, correct me if I am wrong the article you referred to is for Yaesu. Most or all hams I talk with on AM with Kenwood work well out of the box with no modifications. They won't modulate like a Valiant or Five Hundred but they do work good for a rice box and better than my Icom. 73 de k7iou

Hi Dave,

Sure, the Kenwood will "work OK" on AM stock. But sweep it and you will find that the response is lacking from perfect.  If we go thru the stock mic input into the stock audio, it will have limitations.  The AM filter is probably the same.  Some of the balanced modulators on AM have IMD problems too.  Ask Steve WA1QIX about the distortion he found on a Yaesu FT-101 and the mods he did to get that balanced modulator right. The NE-602 board solves all that.  

However, they all will still suffer from the DSB wavelets problem when modulated too heavily.  A low level negative peak limiter is required. That is another subject.

The NE-602 board will work with any I.F., as long as the board is built for the proper frequency -  Yaesu, Kenwood, Icom, or whatever.  The NE-602 board mod makes it easy to get a perfect and very clean response right from the start.

I would think the best way to approach any ricebox modification for AM is to first sweep it stock with an audio signal generator and see how it does. This may be good enuff for some guys. Others may want a broader response and can start changing things and look at the response again until satisfied.

Personally, I would not settle for less than 1 Hz to 20Khz flat with next to nil IMD products. Then use an outboard audio EQ to tailor the audio where we need.  It's not hard to get perfection with a modified ricebox and theoretically it should sound better than the best class E or plate modulated rig out there.  We are using low level "precision" chips here. The linear amplifier RF power stages afterwards are also cleaner than any high level AM rigs, as long as the linear amps are properly designed, run conservatively and  adjusted for best IMD.

SDR transmitters are also good on AM right out of the box, once adjusted properly - no fussing.

T

[Edward Cain]

Thank you all for your input. I now have access to all the information I need.

Ed