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Kenwood TS-430 Modifications

This article first appeared in CQ BARS, newsletter of Bolingbrook Amateur Radio Society, in September 1989. If you come across a second-hand TS-430, it could still be helpful. Be warned though -- you'll probably have a hard time finding new accessories such as the optional IF filters or FM adapter these days.

TS-430 Mods (1989)

ts430.jpg (5765 bytes)The TS-430S is a fine little solid-state HF transceiver which was discontinued by Kenwood a couple of years ago. This mobile or fixed station set has two VFOs and eight memory channels, with a general-coverage receive range of 150 kHz to 30 MHz. Power output on the HF amateur bands is around 100 watts PEP. Second-hand prices vary from $500 to $1000 depending on the number of bolt-on goodies included, such as the matching PS-430 power supply or the AT-250 automatic antenna tuner.

If you are lucky enought to acquire a TS-430S, here are a few suggestions to improve the performance. First of all, check which filters have been fitted by the previous owner. The standard 2.4 kHz SSB filter can be supplemented by a 6kHz YK-88A AM filter, a 1.8 kHz narrow SSB filter (YK-88SN) and by 500 Hz or 270 Hz CW filters (YK-88C, YK-88CN). These filters are still available off the shelf for the Kenwood TS-440S and R-5000. Filters from other manufacturers are not recommended. They may be the wrong physical size and have poor performance. Incidentally, the FM-430 optional FM adapter is still available from AES.

The Instruction Manual contains a couple of useful hints. If you would like the frequency display to show 10 Hz resolution instead of 100 Hz, simply cut a jumper on the control unit board. To transmit as well as receive on the 18.06 MHz and 24.89 MHz WARC bands, cut the white jumper on the RF unit.

If you would like unrestricted HF transmit coverage (and remember that even if licensed, you must never transmit outside the amateur bands on non-type accepted equipment except in an emergency!), WB6NOA in March '87 WorldRadio suggests unplugging the RF Unit connector #10, though the Kenwood factory indicates that a safer mod would be to clip D39 near this connector then locate IC-2 on the Control Unit (under the IF Unit) and snip resistor R-148 near IC-2. This same article also gives mods for general-coverage transmit with other popular transceivers.

If you would like to extend receive coverage below 150 kHz, search out the PLL Unit at the bottom of the transceiver and cut one end of resistor R52, 47k. The receiver will now tune below 150 kHz and you should be able to hear pulses from the LORAN navigation system, around 100 kHz. Sensitivity isn't wonderful, and there are quite a few birdies, but at least you can hear things! (This modification originated with N7ETV, in the IRT Kenwood newsletter, reprinted in 73 July '89.)

Incidentally, if you connect the earphone socket of a portable FM radio (mono) to the antenna input of any general-coverage receiver or transceiver with LF coverage, then tune the portable to a local VHF-FM radio station, you should be able to hear the stereo difference signal sidebands (L - R) around 38 kHz on the general coverage RX. You can also check for the presence of SCA (Subsidiary Communications Authorization) subcarriers carrying background music, data or specialist talk-channels by tuning around 67 or 90 kHz with the general coverage receiver on FM! (But don't listen to the contents.) This works fine on a modified TS-430:

ts430pix.jpg (8800 bytes)

One of the advantages of a general coverage receiver is the ability to listen to short-wave broadcasters from around the world on AM. The TS-430 gives a very good performance with the optional AM filter, but the bass response is poor, which is unfortunate if you are listening on a large speaker. To improve the bass response, locate the IF Unit and increase C45 (.047mF) to a l0mF tantalum then increase C57 from 0.47 mF to 2.2 mF. You can strap the new components in parallel with the existing ones. Watch the polarity on electrolytic capacitors! This modification also makes it easier to tune carriers to zero-beat against the BFO on SSB.

Finally, there is one other source of quality AM signals, and that is the standard AM broadcast band of 540 to 1590 kHz. In my TS-430, the sensitivity dropped considerably when tuning between 500 kHz and 1600 kHz.Apart from making distant AM broadcasts inaudible, this also spoils reception of NAVTEX navigational telex transmissions on 518 kHz. The cause was the attenuator circuit in the RF unit's 0.5-1.6 MHz bandpass filter; although the circuit says R7 should be 22W , a 220W resistor had been installed. Bridging this resistor with 27W improved the sensitivity to a very respectable level, and there is almost no change now in S-meter reading as the dial is tuned past 500 or past 1600 kHz.

Let me know if you find any of these TS-430 mods useful… (and tell me if you come across any other good ones!)

- 73 de Malcolm, NM9J

G3VNQ-NM9J amateur radio site, 05-Jun-2007