Interface performance including analyser noise plots and real-time captures of data on an XGGCOMMS.COM interface compared to the competition

Noise Performance

One of the major concerns hams have regarding this type of Computer-to-Radio interface is the possible computer noise and interference that it may generate in your receiver. The last thing you need to hear is "computer buzz" when you are trying to dig out that weak signal. I have thoroughly tested my interfaces and they are interference free. I have tested my interface on an Agilent ESA Spectrum analyser and have produced these screen grabs to demonstrate the clean nature of the interface. Trace 1 shows the 40M band straight off my antenna.  (I have put a marker on the 40M PSK31 frequency of 7.035MHz as a reference).Trace 2 is the analyser connected to the interface output to check what unwanted signals the computer/CI-V interface might be generating. This is done within the same band and with all the same settings as Trace 1.

As you can see, all that is present in Trace 2 is the noise floor of the analyser at around -111dBm. There are no measurable signal spikes or electronic noise being generated by the CI-V interface or PC that can be measured by my test equipment.

I have had a number of customers who have purchased my interface because they found other interfaces in the marketplace were "noisy" and have commented that the noise performance on this interface is superior.



Spectrum Analyser Trace 1 (off antenna)


Spectrum Analyser Trace 2 (off CI-V port)


Data Performance

The interface works 100% reliably at the highest Baud Rates on the supported radios. The double sided interface PCB is housed within in the 9 Pin D Type Shell and is constructed using surface mount components. All of my interfaces are thoroughly tested on Laptop and Desktop PC's before shipping. The interface is designed to minimise any chance of damage to your radio or PC. This photo below is a close up of the internals of the interface for those who are interested to see how it fits in the shell. The side of the PCB facing up has the PTT/CW Keying circuit and the underside contains the RS-232 to CI-V circuit.




One huge benefit with this type of interface is that it is powered via the PC serial port. However, this can also be the achilles heel on poorer interface designs. Laptops have notoriously fussy serial ports and so can produce lower supply voltage and have reduced current drive ability. Some Dell laptops fall squarely into this category. I know because I own one.

I have found through experience and by feedback from my customers that some competing designs struggle to work on laptops. I purchased a competitors design and it failed to work at all on my Dell Latitude and so I though I would have a look on the storage oscilloscope.

These comparison traces were done with my PC driving the interface as I could not even get the competing design to fire data across the CI-V bus whilst using my Dell Latitude.

The traces are data captures from the interface as measured on the data input pin on the radio CI-V/CAT Jack.

The Trace on the left is from my interface
As you can see, it is producing a nice shaped pulses with no ringing or poor rise/fall time issues.

The Trace on the right is a competing interface
It is obvious that the pulse shape is poor with very slow rise times. This may be due to it asking too much of the drive capabilities of the serial port even on my desktop PC. With this sort of performance, it had little chance of working on my Dell Laptop. I suspect this competing design may have issues with occasional errored data even on a normal PC serial port judging by the poor pulse shape.



 Leading Competitors Trace