22 November 2020


 A few months ago I purchased the PTRX-7300 panadapter interface board for the Icom IC-7300 from DXEngineering. The PTRX-7300 is manufactured in Europe by a company called RadioAnalog. The board is installed in the 7300 (no soldering required!) and it 'sniffs' the incoming RF without otherwise burdening the radio (the 7300 doesn't even know it's there). The PTRX-7300 outputs that RX signal tap to an external software defined receiver (SDR) of your choice. With the SDR radio connected to a computer and running SDR software you now have a panadapter display that is shows not just the small slice of the amateur radio band visible on the IC-7300's front panel, you get to see the entire band in one view. Even better, the incoming RF line that the PTRX-7300 'sniffs' is tied to the radio's RX/TX circuit. When you transmit on the 7300 the RX circuit is shut down, so the PTRX-7300 is protected.

About a week ago I found the time to open up my IC-7300 and do the install. I had read reports and watched YouTube videos that talked about how easy the installation is. They were all right. It literally took me more time to get all the screws out of the IC-7300 case than it did to install the PTRX-7300. The board is extremely well designed and built, and very cleverly ports the RF 'tap' out through the radio's external tuner port. Don't worry, you can still use an external tuner. You just end up with an extra cable that you connect the tuner to. It all works just fine.

For an SDR, you can use whatever you want, even one of the inexpensive SDR dongles like the RTL-SDR. However, keep in mind that many of the SDR dongles are optimized for VHF & UHF frequencies and don't do well in the HF spectrum. I chose to use an SDRPlay RSP2 that I've had for a few years. The RSP2 is a single receiver/two anetnna input design, which works great in this application. The RSP2 has been discontinued, and is replaced in the SDRPlay lineup by the RSPdx. Hmmm... may have to ask Santa for an upgrade.

SDRPlay also develops the SDRuno software application that drives their line of receivers. This application is best-in-class for controlling SDR receivers (and not just SDRPlay units, but the software can also control other receiver models, like the RTL-SDR units). Even better - the application is free! The SDRuno user interface can be a bit daunting at first, but within just a few operating sessions you'll have it down.

So let's see how this all goes together.

The PTRX-7300 board installed. The install kit includes all necessary cables

The cable on the left is the external tuner extension.
The cable on the right is the RF 'tap' cable that connects
to your SDR

Everything buttoned up and showing the cabling

View showing the RSP2pro connected to the IC-7300. For convenience, I attached the receiver to
the 7300 using double-sided tape

Once all the hardware is connected it's time to take a look at the software. The SDRuno application is Omni-Rig 'compliant', which means if SDRuno sees the Omni-Rig software running, it automatically slaves itself to the rig control software. All you have to do is configure your IC-7300 as RIG 1 in the Omni-Rig interface and the 7300 and SDRuno will be driven simultaneously by Omni-Rig. Change frequencies on the radio, SDRuno follows along. Change to a new band in Omni-Rig, the 7300 follows along. You get the idea.

Configure Omni-Rig to sync with
the IC-7300 as RIG1.
The RSP2 acts as a sub-receiver, controlled
via Omni-Rig

When launched, SDRuno is a sea of floating windows, but that's one of the keys to its versatility. You can launch multiple virtual receivers, each with its own panadapter window, you can tweak the passband settings, you can install and manage frequency libraries, and lots more. Basic functionality is easy to figure out; the more complex functions involve a bit of a learning curve.

One of the neat features introduced with the newest version of SDRuno is the ability to use third party plug-ins. For example, SDRuno can not decode any digital modes like FT8 or PSK. It can hear them, but can't make sense of them. With the third party plug-in concept, a developer can make an FT8 plug-in and you will be able to decode FT8 traffic right within the SDRuno interface. The SDRuno install packages includes a few 'trial' plug-ins, and in the image below I'm running the DXCluster plug-in. It superimposes DX stations on the panadapter display, making it easy to visulaize them in relation to the spectrum. I'm really eager to see what other developers bring to this new plug-in environment.

Note the DXCluster indicators in the right side of the panadapter display.
I'm using the DXCluster plug-in to display the stations on a 5 minute refresh interval

One of the neat tricks you can do with a dual-antenna input receiver like the RSP2 is run the receiver without the IC-7300 in the chain. This allows you to poke around the band and frequency segments that the IC-7300 can't handle, like VHF and UHF. The concept is simple, and there's no need to plug or unplug cables or re-configure software. Just choose 'ANT2' (antenna 2) in the SDRuno interface to bypass the IC-7300:

Wire up the IC-7300 and the RSP2 via the ANT1 connector on the RSP2 to
make it a sub-receiver controlled by Omni-Rig

Want to explore frequencies beyond the IC-7300's capabilities? Just turn off the 7300 and switch
over to ANT2. You'll have to push the audio through your computer speakers vs. the 7300

I'm still playing around with and tweaking this setup, and I have run up against a few issues users need to be aware of:

  • You need to set your matching baud rates in both the SDRuno interface and the Omni-Rig settings, and they must match what's set on the IC-7300. If all three don't match then SDRuno will kinda'-sorta' look like it's running properly, then stop responding. It took me a day or two to figure this out
  • For some reason, either SDRuno or Omni-Rig changes the IC-7300 CI-V Transcieve mode to OFF (default is ON). While this doesn't impact voice transmissions, it does lock out TX controlled by digital mode software like Fldigi or JS8Call. I'm still trying to troubleshoot this issue, but it's easy to reset the CI-V Transcieve mode back to ON from the radio's front panel display (it's under the 'Connectors' menu setting)
  • I have not tested this IC-7300 - Omni-Rig - SDRuno setup in conjunction with digital mode software such as Fldigi or Winlink; I'm not sure yet if you can simultaneously run another software application that requires control of the radio's settings. After I test I'll report back
So that's it for now. My overall opinion of the PTRX-7300 add-on board is pretty good. It's a very well designed and built piece of hardware that adds real capabilities to the IC-7300 setup. If you want a panadapter for your IC-7300 this is the most versatile and elegant way to get it. Highly recommended.

W8BYH out

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