This article describes the audio configuration of the TS2000 at VK1OD in May 2008.
The dynamic hand mic supplied with the TS2000 is quite susceptible to magnetic flux, and leakage from the nearby AL-811H amplifier results in low level hum in the transmit audio depending on the proximity and orientation of the microphone.
A number of options were explored for solving this problem, and the one currently pursued is a condenser microphone.
Fig 1 shows the Behringer C-2 microphone. It is a condenser microphone and requires phantom power for the internal preamp. The microphone is quite small, about the same diameter as the XLR connector that plugs into the end, and weighs less than 100g so it is comfortable to hand hold and suited to mounting in a mic stand. These sell online for about A$120 a pair. The microphone is used with the supplied foam filter to minimise pops.
I have also tried a Behringer C-1 and Behringer C-3 and they work fine.
Fig 2 shows the MIC800 preamp. These sell online for about A$80. It provides phantom power for the microphone and a low cut filter. The low cut filter is set to the 3 o'clock position, otherwise the preamp is set for flat response. The preamp shows a little susceptibility to RFI, and needs treatment of some of the cables connected to the box.
Fig 3 shows a choke applied to the MIC800 power cable, it is a LF1294 snap on sleeve. Note there are four turns of the power cable through the choke.
Fig 4 shows a choke applied to the microphone cable just adjacent to the MIC800. The choke is two Jaycar LF1260 cores with a little heatshrink sleeve to hold the cores in place.
The microphone interface on most radios is very sensitive to ingress of RF, and the TS2000 is no exception. Fig 5 shows a choke made with a Jaycar LF1260 ferrite suppression sleeve, and the two shielded cables make two turns through the sleeve then shrink sleeving is applied to finish off. A 40dB attenuator is built into the plug taking the audio from the MIC800 to drop the audio level back down to microphone level for the TS2000. The attenuator has an equivalent source impedance of 1kΩ to emulate the original microphone.
A footswitch is used for the PTT. The footswitch is a Daphon 1772 Sustain Pedal. These sell online for about A$20. This pedal has a switch to select NO or NC operation, and does not contain a pot (as do some sustain pedals).
The TS2000 is fitted with a Roger Beep chip which has TAPnYAP, so the footswitch can have latching action logically.
The preamp is located on top of the TS2000 and a short RF ground lead is connected from the preamp output plug to the back of the TS2000. This ground lead has a 0.01μF capacitor in series to prevent a hum loop.
Observers offering flattering audio reports often attribute the signal quality to the non-standard audio setup. In fact, the non-standard audio setup doesn't sound very different to the original microphone.
The transmitter is normally used with the Speech Processor active.
A test was conducted by speaking a test message into both microphones and recording the tx audio from the TX MONI output. Fig 7 shows the spectral distribution of the test message firstly on the C-2 microphone and then on the original Kenwood hand mic. There is very little difference in the spectral content.
Click on the link to listen to the test message recording. Note that most receivers will hear even less content below 300Hz due to the IF filter.
Audio quality is mainly attributable to appropriate adjustment of audio levels and drive level to the PA to minimise the risk of overdrive.
The process is:
The AL811H ALC is connected to the TS2000, but is adjusted so that it will not develop control voltage until well above 400W PEP, it is a measure for reducing grid damage from accidental gross overdrive rather than normal power control. (The ALC response is way to slow to use it effectively for normal power control.)
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