For quite awhile I have "dreamed" of adding an SDR in my station to enhance the operation of my Kenwood TS-480. I started down the path of a SoftRock wired into the IF of the TS480 but I was not excited about tinkering inside my Kenwood, so the panadapter project went on the back burner. After reading W9RAN's article "Cheap and Easy SDR in January 2013 QST, I went out and bought a DVB-T dongle. I also purchased the Opendous upconverter.
I was already using HRD to control my TS480, so I got see away to sync the two receivers. For the SDR control, I am using HDSDR. Omnirig software allows HDSDR to also communicate with the TS480 through HRD. This requires the use of virtual comm port software. I am using free software, Eterlogic's Virtual Serial Ports Emulator. I set up a virtual comm port, which is paired with com 1, which is used from the TS480 to HRD. Virtual Serial Ports Emulator then allows other applications to bidirectionally share the virtual com port. Omni-rig in HDSDR then allows the configuration where HDSDR will sync bidirectionally with HRD.
After getting that to work and "playing around" for awhile with the SDR, I build the LZ1AQ Splitter Box to allow the Kenwood TS480 and the SDR to share the same receive antenna. http://www.lz1aq.signacor.com/docs/Integrating-Software-Defined-Radio_II_HP_eng/Integrating%20Software%20Defined%20Radio_II_v41.htm
Since I was only using the SDR for a visual display and for the "point and click" selection of a station from the waterfall, I didn't build the circuit that LZ1AQ added for controlling the switching and muting of the headset. The Splitter Box uses a coax T connector, which I have between my TS480 and my homebrew solid state linear. The Splitter Box feeds the signal through a wide-band transformer and a low wattage attenuator to the SDR. An inverting Schmidt trigger is used to take the PTT input from the transceiver, eliminate any bounce, and control a relay that shorts the input to the SDR when transmitting. To add further protection of the SDR, I put two diodes back to back across the SDR antenna input.
To say that I am happy with the final project would be a big understatement. I have only been using this for a day now, but I have used it on all bands that I operate on HF. The LZ1AQ Splitter Box is between my TS480 and my homebrew 600 watt solid state linear. I had numerous QSO's today on 20, 15, and 10 meters and what a joy it is to be able to see at a glance if a band is open and quickly point and click to select a station. I don't know how I got a long without this functionality. I can see now why people spend the big bucks on the high-end, dual receivers with a panadapter display. With this low-cost setup, anyone can have that functionality using a low-end transceiver and a dongle SDR at very low-cost.
With the two receivers in parallel, you are going to have a little over 3db of loss when using the SDR panadapter. A toggle switch on the Splitter Box will short out the SDR and eliminate this loss if you need to pull a station out of the noise.
Enough said, it is time to go back to playing with my SDR panadapter and enjoying ham radio. If you want to try this and have any questions, drop me an email at firstname.lastname@example.org
and I will be glad to help.