TS-440S SDR: a testimonial by IK2TIF

TS-440S SDR: a testimonial by IK2TIF

Below are the notes relating to the installation of the IFace interface inside the Kenwood TS-440S by IK2TIF Fabio. In general this work is done in order to be able to extract an IF signal from the radio reception chain so that it can be used to make an SDR panadapter and add an external SDR receiver. The application scheme is shown in the following image.

The signal to be sent to the external SDR receiver is picked up immediately after the first receiving mixer and the frequency it will be tuned to will be 45.05 MHz.

The RF signal at the mixer output is taken between the transformer T3 and the anode of the diode D26.

The task of the IFace buffer card is to supply the necessary power in order to correctly drive the circuits of the external SDR receiver: in general, the intensities of the signals of interest are small fractions of mW. During transmission, on the other hand, there are powers of the order of tens of W or even more, and this can be a problem for the external receiver, especially if it is working in isofrequency with the radio. Therefore it is good to use the PTT signal to disable the buffer, a unique feature of the IFace. It is therefore necessary to identify the point inside the radio where to take this signal. Nothing could be easier, the TXB signal is present on the J1 connector and this is active high only during transmission.

Having to supply power, the IFace must also be suitably powered. From connector J6 it is possible to obtain the necessary potential difference from pins 14J and GND.

Below are some images useful for identifying the points on the RF UNIT where to intervene to take the various signals: IF, PTT and power supply. As for the IF signal, it should be noted that even IK2TIF has not used a coaxial cable to connect the IFace input to the mixer output. In this way it is possible to minimize, also thanks to a very short connection, the parasitic capacitance which is placed in parallel with the mixer output. If this were not negligible, there would be a strong attenuation of the IF signal and a general degradation of the receiver’s performance.

This image shows how to connect the IF signal to the IFace. A thin conductor (0.14 mm) covered in plastic material is used. As already highlighted, it is not recommended to use a coaxial cable because it introduces a non-negligible capacitance in parallel with the components of the mixer circuit and would modify their performance. The coaxial cable can instead be safely used as an output from the IFace.

The power cable of the card is shown in red and the following two images are related to the installation in the TS-440S.

The PTT signal enters the IFace via a thin yellow wire placed in parallel directly in the connector.

The IFace board can be fixed to an RF circuit cover plate: be careful not to short-circuit some contacts located on the underside of the board (you can use double-sided tape).

Infini you connect the external SDR receiver and start the software. The following images show the TS-440S and the SDR software screen.

In the image above it is very clear the number of stations that can be received and displayed in the waterfall of the SDR radio. The excellent installation carried out by IK2TIF is evident from the absence of unwanted signals and artifacts in the spectrum.

To purchase an IFace you can use the following buttons.

ATTENTION: Although the installation of IFace 2 is not difficult, it is done at your own risk. TSP S.r.l. is not responsible for any damage, unwanted side effects, or anything else.


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