Here we are talking about how to interface a decidedly dated radio to one of those SDR receivers on USB like the well-known RTL-SDR as already done for Yaesu FT-450D in this article . The software to be used on the computer can be chosen from SDR #, SDR Console, HDSDR or others.

Panadapter SDR for TS-530S

40 years ago radio did not have displays on which to show the waterfall of the band we are working on. In some cases it was possible to buy accessories such as spectrum analyzers, but it ended there. With the IFace interface of TSP it is instead possible to add digital filters in reception, spectrum analyzer and waterfall around the frequency set on our radio and also add more receivers so to operate in split-frequency (for example) or listen to more QSOs at the same time.

How to do it? Or rather, what does the IFace interface consist of?

In most of the work published on the network, it is proposed to pick up the signal from the radio’s average frequency. And on this I think we can not disagree. Obviously the sampling should be done at the output of the mixer but before the medium frequency filter, otherwise goodbye broadband spectrum. Others propose to connect to the input of the first mixer, after the pre-amplification and band-filtering stages: in this way they take advantage of the frequency agility of the SDR receiver to tune to where they prefer (regardless of the VFO). But there is a drawback, after the band filters there is no longer all the available HF spectrum but only a small portion. For example, in other bands, VHF and UHF, the speech can make sense because the ratio between the bandwidth and the central frequency (ex: 2 MHz to 145 MHz) is much lower.

In any case this ” “signal” should be done well by limiting the undesirable effects on the reception chain of our radio (decrease in signal strength, change in impedance etc) but not all is clear this concept. The result that can be obtained is shown in this video.

In short, the IFace is a buffer, that is a circuit with unit gain that replicates the input signal at the output without going to load the source circuit. This is very important because going to alter the load seen by the medium-frequency circuits of any receiver in general is never a good thing. In fact, radiofrequency circuits often modify their frequency response depending on the load impedance. Therefore, in order not to “disturb” the operation of our RTX we will have to tap as little power as possible from the receiving circuit and to do so a buffer is needed, that is a circuit that makes a copy of the signal “without altering it”.

The signal that we will have to replicate is that of medium frequency and more precisely the first so as not to have limitations on bandwidth due to IF filters. We will therefore have to take the wiring diagram of our radio and find the exact point where to pick up the signal: in general it is at the output of the medium frequency mixer.

Panadapter SDR for TS-530S
Panadapter SDR for TS-530S

The following images show where this point is located in the TS-530s. The first shows the inside of the radio, the second the layout of the medium frequency board.

Panadapter SDR for TS-530S
Panadapter SDR for TS-530S

Next, small coaxial cables are soldered between this point at the mixer output and the IFace entrance, between the IFace exit and a coaxial connector for sending the signal to the SDR receiver and those for power supply. All this is shown in the following images.

Once the editing is finished, the result is visible in this video.

 

All this can be easily migrated to any other RTX: in other articles we will talk about it.
For questions or Curiosity write me or visit www.tspelettronica.com .

Best 73 de IZ0ABD

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