Connect a second SDR receiver to your IC-7300
ic-7300 external panadapter . Many people complain about the lack of the possibility to connect a large display or a SDR receiver to the ICOM IC-7300.
The IC-7300 has no RX2 output, but fortunately it is possible to have access to the main board RF input after the preselector filters and LNA/Attenuator.
Some “on the shelf interfaces” are available at relatively high price. They need to modify the tuner output connector.
The purpose of this smart interface is quite the same, without external modifications or drilling in the cabinet.
ic-7300 external panadapter
No degradation of the IC 7300 specifications (sensitivity, spurious, etc.) after installation of the interface.
Audible weak signals shall be seen above the noise floor i.e. about -135dBm antenna RF input Absence of spurious in 1MHz bandwidth when the antenna is disconnected.
Output frequency between 1 and 60 MHz
Installation must be easily reversible.
Needs few components only, easy to find.
ic-7300 smart panadapter SCHEMATIC
Figure shows the solution used to avoid any drilling in the die cast cabinet: we use the “SEND” output connector normally used to make the PTT of a linear amplifier. This out put is connected to the NO contacts of the PTT relay via a choke coil and to the GND of the IC 7300.
During reception the contacts are open and the output RF signals are sent to the external receiver.
During transmission the contacts are closed and the output is connected to the ground via the ferrite bead EP102_MPZ2012S601A (600Ω at 100MHz), so the signal can be monitored even during the PTT command.
To avoid any loading of the RF at J1431 connection, we use a JFET BF245B in common drain impedance adapter.
The RF signals are “sniffed” directly on J1431; the corresponding pad is directly connected to the gate of the BF245B with an input impedance close to 50KΩ.
The output is picked directly on the source of the BF245B via 100nF and routed to the SEND connector thanks to a thin coax cable. To prevent against possible high voltage coming from the linear relay in case of PTT, two 1N1711 schottky diodes are connected between source and ground.
Keying a linear amplifier remains possible using a bias tee.
A brass spacer is installed on the RF board
The components are soldered on a small PC board; the board is fixed on the spacer making the GND connection.
TRANSMISSION TEST FROM ANTENNA TO PANADAPTER
The paths from the antenna input of the IC-7300 to the RF board output (J1431) or to the SEND connector are swiped with the spectrum analyzer and its trigger generator. The traces are recorded in max hold mode while the IC-7300 is tuned between 10KHz and 70MHz. The LNA is off.
The two traces are similar. We see that the output of the interface follows the antenna input with 3 to 4 dB difference; this is not an issue because the external receiver will keep the same C/N ratio.
This description aims to give a low-cost alternative to the “on the shelf’ IC 7300 panadapter interfaces. In needs only 3 soldering points on the RF board and no drilling in the die cast cabinet. It is completely reversible. It doesn’t degrade the performances of the IC 7300.
Used with a SDR receiver, it is possible to monitor a larger span than the IC 7300 and more accurate.
Used with Omni Rig, the panadapter RX can track the IC 7300 and some settings of the IC 7300 can be sent by the panadapter directly.
The modification will be made at his own risk and without incurring the responsibility of the author.
Download document in PDF format with all images of the assembly