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AMfone's Online AM Handbook => Modern Rigs => Topic started by: W1AEX on December 05, 2012, 03:24:51 PM

Title: Kenwood TS-590S Performance on AM
Post by: W1AEX on December 05, 2012, 03:24:51 PM
There’s not much that has to be done to an out-of-the-box Kenwood TS-590S to get decent results on AM. As with most current multi-mode rigs the DSP limits the total transmitted bandwidth to 6 KHz on AM, however, the receiver allows you to listen with a bandwidth of 10 KHz. A very nice feature of the receiver is that you can make direct recordings to software such as Audacity or Adobe Audition on your computer by utilizing a USB cable and the Kenwood audio codec that is present after you install the free drivers and software from the Kenwood web site. The sound quality of the recordings is excellent.

When transmitting with the AM mode I found it was necessary to increase the MIC gain level to 75 to reach 100% modulation. This is a substantial increase over the nominal level of 30 that I use with sideband. It was also necessary to reduce the carrier level setting to 15 to restrain the ALC from its tendency to clip peaks. Both of these settings are accessed from the front panel by either a short press (mic level) or a long press (carrier level) of the MIC button. Note that adjusting the carrier level setting for AM will also affect your power output with the CW mode, so after running AM you will want to raise it back to around 20 to assure that you can reach full output when transmitting with CW. My settings for running AM are listed below:

On the front panel:
MIC level – 75
CAR level – 15
PWR level – 25 (maximum)

In the user menu:
Menu item 25 – set to 10
Menu item 26 – set to 3000

The above settings resulted in an RF power output level of 12 watts carrier with peaks reaching just over 50 watts when fully modulated, as measured with a Nye RF Power Monitor.

I made a video/audio recording of the TS-590S using the above settings to provide an idea of how it sounds when running AM. The recording was made with a Flex 5000A running PowerSDR (version 2.2.4) set for a bandwidth of 8 KHz in the synchronous AM mode. You can see how the TS-590S looks in the panadapter and hear the audio as well. The microphone used with the TS-590S is a cheap electret element plugged into the front panel mic connector. I used an EQ transmit profile that I created with the free Kenwood ARCP-590 software that drops the low end response by –9 dB and raises the upper mid-range audio areas by 4 dB to attain audio that is fairly natural.

The MP3 file that is attached is a sample from the AM broadcast band of ESPN radio recorded with Adobe Audition through the USB cable connected between the TS-590S and my computer. The bandwidth of the TS-590S was set to its maximum value of 5000 which equates to 10 KHz in the AM mode.

Running AM with a stock TS-590S is not a tragic experience and most of the reports I get from stations on the other end are good. It would be interesting to see if someone can figure out how to modulate the power control FET to bypass the restrictions imposed by the DSP when transmitting AM. With such a nice sounding receiver, that would be a deluxe development!


Title: Re: Kenwood TS-590S Performance on AM
Post by: Ka2zni on December 11, 2018, 11:53:47 PM
I've been waiting for the same thing... I can't find any way to defeat the DSP for broader transmit bandwidth on AM...

Title: Re: Kenwood TS-590S Performance on AM
Post by: KD6VXI on January 13, 2019, 07:56:27 PM
Problem I see with this is:  If they use bipolar devices in the final stage (improbable honestly) , you'll need to modulate a preceeding stage as well to get full modulation.  If they use fets in the final, you'll need to rebias the amplifier to class C, no?


Title: Re: Kenwood TS-590S Performance on AM
Post by: W1AEX on January 15, 2019, 03:33:45 PM
The 590S and 590SG use a pair of RD100HHF1 mosfet devices in the final. They are very rugged and nearly indestructible (also used in the Flex rigs, ANAN 100 watt PA decks, along with some ICOM and Yaesu rigs) and a pair can easily handle the usual amateur 100 watt service. What some have done (Rick VE6CQ and Phil W2PHL come to mind) is to leave the PA deck biased for linear service and then modulate the power control FET. Rick did this with an ICOM and as I recall Phil did this with a Yaesu FT-847. A few years back I stumbled upon a web page with an easy modification that was done to a Kenwood TS-940 by running the VCC for the power control FET through the secondary of an audio transformer and then external rack audio was applied to the primary of that transformer. I'm not sure how Rick and Phil did their rigs but when I worked them they sounded great. I'll bet the same technique could be done with the 590S as well but I have never bothered to look at the schematic to see what would be involved.

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