Better PTRX-7300 with better price!

As a ham radio operator, you may already know that ICOM IC-7300 is one of the most popular radio rig in the world. In addition to this, you may be one of the user of this commonly used radio equipment. On the other hand due to lack of RF output support capabilities of IC-7300, you may feel restricted for your ability to use SDR receivers such as AirSpy, HackRF, RTL-SDR, SDRplay and software like HDSDR, SDRuno, SDRSharp, GNURadio as well. As a result, we would like to fill in this gap by designing a high impedance signal probing product PTRX-7300 to help ham radio operators to utilize their IC-7300 with full SDR functionality.

For detailed installation manual, please click here.

PTRX-7300 utilizes active high impedance current-feedback probing technique to probe bidirectional TX/RX signal line of IC-7300 (J1431). Due to high impedance nature of the unit, you do not introduce any insertion loss. Therefore there is no adverse affects on the radio side in terms of signal quality. In this method, there isn’t any 3dB insertion loss as in power splitting approach to probe the signal.  You can see the block diagram in Figure. 1.

PTRX 7300 Installation Diagram by RadioSpectral
Figure. 1: PTRX-7300 block diagram.

During the design phase, we first measured dynamic range of TX/RX line (J1431) of IC-7300 in terms of both voltage and frequency. Once we extract these information to define design specification of the unit, we developed proof of concept designs with helping SPICE simulations. In these simulations, we took into account both signal integrity and amplification characteristics. With helping DDS based signal generator (30kHz to 120MHz, @980mVpp), we analyzed signal quality in both time and frequency domain

Our high impedance probe has been designed with components from reputable distributors, such as Digi-Key in order to maintain highest level of component quality. One of the major observation during testing the unit, we saw input/output MCX connectors have vital role to generate distortion/attenuation free signal. Please look at the Figure.7 for design and quality details. Any counterfeit/low quality MCX connectors result extremely poor signal quality.  You can see the proof of concept design regarding development of the unit in Figure.3.

Full view of PTRX 7300
Figure. 2: Actual PTRX-7300 set.
3D CAD Model of PTRX 7300
Figure. 3: CAD model of PTRX-7300.

Design process happened without compromising external tuner functionality. Therefore schematics and the mechanical model have been designed for IC-7300 external tuner opening.

Simply it bypasses external tuner cables to outside, so you do not lose any external tuner functionality. It requires 13.8V DC to operate. For this reason, we utilize power line from external tuner cable without adding external power supply to the unit which consumes up to 30 mA from external tuner cable so it does not disturb your tuner operations. You can see the details in Figure.4.

Installed PTRX 7300 on ICOM IC-7300
Figure. 4: Installed PTRX-7300.
Rear view of installed PTRX 7300
Figure. 5: Rear view of installed PTRX-7300 into IC-7300.


As we mentioned before we applied variable test signals in order to simulate extreme conditions. IC-7300 can operate between frequency range 30kHz and 74.8MHz (up to 500mVpp), but we tested, ranges varying from 30kHz to 120MHz (@980mVpp). We make sure that the unit has flat frequency response for this range. Please watch our test video called “PTRX-7300 Frequency Response.

Our test also covers AM and DRM demodulation on actual HF band conditions. As we come to testing CAT control synchronization with SDR software, we used OmniRig with HDSDR.

PTRX 7300 and SDR connection
Figure. 6: SDR connection for PTRX-7300.


Radio Spectral PTRX-7300 Comparison with the Competitor
Figure. 7: Comparison of RadioSPECTRAL PTRX-7300 with competitor.
Figure. 8: Time domain comparion for PTRX-7300s. Yellow trace is from RadioSPECTRAL, green trace is the input signal.

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