I have always been a big fan of computerization. In my video production business, I was an early adopter of the Newtek Video Toaster. When I was a DJ, I was one of the first people in my area to have a mobile PC-based DJ system. I have been using PC-based audio and show control solutions for theatrical productions for 20+ years… so why would my ham radio shack be any different.
One of the neat things with Software Defined Radio (SDR) technology is that it seems to be reducing the expense for someone to get a really good receiver.. I’ve touched a few of the really high end radios at Hamvention… but I doubt that a $10,000+ rig is in my near-future radio budget. Part of of my reason for starting this website and posting my shack design and progress, is to highlight the ability of a radio operator to make some incremental additions, and to work towards a reasonably high quality HF station.
If you’ve read my recent posts about my first contest experience, this interface was inspired by my difficulties with transmit/receive switching. I found a a really good site by WS4E about interfacing an FT-450 to a Softrock. Most of the basis of this project is based upon the work that he had already done.
The idea is to tap an internal point in the radio that is after the bandpass filters and before the initial IF stages. This will allow an external SDR receiver to connect to the same antenna as your transceiver. The tap point is already after the internal T/R relay, so there is no requirement for additional switching. In fact, the neat thing is that the transceiver and SDR reciever can tune different frequencies simultaneously using the same antenna with this upgrade. The one caveat is that the tap point being after bandpass filtering, your external SDR will be limited to using the same operating band as your transceiver. I don’t consider that to be a limitation, as this fits the way that I plan to use this configuration.
After reading the WS4E post, I made contact with Jack, K8ZOA, of Clifton Laboratories. I ordered two of his Z10000U amplifiers. I mentioned to Jack where I had found his amplifiers and what I was hoping to do. I originally wanted to get the assembled boards in external boxes, as was done on the WS4E site. Jack mentioned that he had a customer mounting the buffer amp internally in an FT-450 and said that it would be advantageous to minimize the legnth of cable from the tap point to the buffer. I took his advice. He provided the buffer, an SMA with attached cable, and an SMA to BNC cable.
First step is to get power for the buffer. The simplest place to get the power was at the input location of power on the top of the radio. There were two small pads right below the large input cables that made for a convenient attachment point. The cable was easy to route from the top of the radio to the bottom where the buffer would be located. There is a hole to provide access to the coax feed from the upper board to the antenna tuner. In the picture it is difficult to see the black lead. The pad layout is symmetrical. It is also possible to just use the connection of the ground stud on the buffer to provide ground, but I provided a positive and ground, in case I had mounting issues.
The next process was to mount the SMA. There is plenty of space in the back and bottom of the radio for the cable and the connector. The one thing that was problematic, was the length of the SMA connector. The aluminum cast housing of the radio was thick enough that I needed to remove the lock-washer and star-washer to allow sufficient length to connect to the external cable.
There was a perfect place to mount the buffer, by using a small metal stand-off. The Z10000U buffer am has a single mounting hole. It doesn’t need anymore as it is a really small board. The standoff was one from parts box that was a leftover from taking old pc’s apart. In the pic, you will also notice that there is another standoff on top of the board. Two reasons: I figured it would provide a small support to prevent the bottom of the case making contact with the board, and the other reason was that I couldn’t find the right size screw to fit the standoff.
After re-assembling the case, I was very happy to find that the FT-450 still worked as it had before my modifications. One of my colleagues actually asked my why I would mod a modern rig like this. I quickly exclaimed that I had purchased the radio used. If it was a brand new rig, with a brand new price tag, I would have been more hesitant to try this. I connected the SDR-IQ to the new SMA connection and it worked as I had hoped. I found an empty frequency, and tuned up. It was easy to see that the T/R switching was working as I had hoped, as the waterfall went blank except for my transmission. I will still need a function to mute the output of the SDR software, as the SDR receiver is still sensitive enough to pickup the local transmitted signal. The good news is that there is no overload of the SDR receiver. I may still consider building a receiver guard type protector for SDR, but even at a full 100 watt output from the FT-450 there was no overload indicator on the SDR-IQ. The performance of the SDR-IQ was so good to start, that it is hard to tell if the addition of the FT-450′s bandpass filters contributes to even better performance. I have a fairly high powered AM station nearby and I would think that receive performance could only be improved by tapping after the bandpass filters.