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Bron: radioanalog.com

PTRX-7300 is utilizing active high impedance probing technique to sample bidirectional TX/RX signal line. Because circuit is just sniffing (not loading RF signal line), thanks to its high input impedance amplifier, it can not be sensed by the rig and has no adverse effect on normal operation. There is no 3 dB loss as in the case of power splitting approach to sample the signal. Amplifier is designed with state of art components for ultra low distortion and low noise. Active and passive components are from well-known vendors, such as Analog Devices, Texas Instruments, AVX, TE Connectivity, etc. Designed CAD model and manufactured product are shown in Figure 1.  Beside designing high performance amplifer, there is also need for proper connectorized access to RF signal line. Fortunately, IC-7300 has a connector on its PCB designated as J1431 where you can sample TX/RX signals. Antenna RX signal reaches this point after passing through input filters and low noise amplifiers. There is also low power TX signal going to Power Amplifier. TX signal level is low enough (<500 mVpeak) to monitor with same SDR hardware.Download PTRX-7300 Installation Guide

Figure 1: PTRX-7300 CAD Model and Assembled Board

Figure 4: PTRX-7300 Block and Wiring DiagramPTRX-7300’s schematics, PCB and mechanical model has been specifically designed for IC-7300. Tuner connector opening of the rig on back panel is used as panadapter mounting hole. Bigger size tuner connector has been replaced with a smaller rectangular one, the MCX RF connector which is carrying RF signal also placed beside it. An aluminium fixture is designed and CNC machined to place panadapter to the tuner opening on the back panel of the rig. Figure 2 is showing mounting scheme. Figure 3 is showing back panel RF and Tuner connections of panadapter. Figure 5 is showing previously mentioned tapping point on schematics, layout and wiring diagram of IC-7300 service manual.

Figure 2: PTRX-7300 installed in ICOM-7300

Figure 3: Rear View of PTRX-7300 after installation

Amplifier circuit of panadapter also needs a DC power supply to operate. Best way to meet supply requirement is to find a connector carrying DC voltage inside the rig rather than using bulky external power supply. For this purpose we discovered that tuner connector designated as J331 is a good candidate on PA UNIT PCB. This connector is originally passed to back panel of the rig for external tuner connection via a cable assembly. We replaced this cable with a new one and passed tuner connector to the output panel again over panadapter PCB. DC power rails available on tuner connector are used as power supply of the amplifier. Amplifier only draws 30 mA current so doesn’t hurt tuner power rails which is capable of supplying more than one ampere current. Figure 4 is showing block and wiring diagram of panadapter.

Figure 5: PCB and Schematic pages of IC-7300 showing RF tapping point

COMPARISON TABLE

The table below is showing comparison between PTRX-7300 and typical antenna signal switching/splitting/routing approaches.

TESTING PTRX-7300

After design and manufacturing period, PTRX-7300 is fistly tested and verified by appliying artificial signals and monitoring output on oscilloscope and spectrum analyzer. Also S-parameter measurements have been conducted in each port. Afterwards PTRX-7300 has been installed and tested in actual working conditions. As hardware RTL-SDR (HF), as software HDSDR and GQRX are used. 

First tests were covering AM and DRM demodulation which intended to show high signal quality of the PTRX-7300. The last test was demonstrating another important feature which is synchronization of IC-7300 and SDR over CAT control. OmniRig free software is used with HDSDR.