Monday, July 4, 2011

FT-450 SDR Interface to Softrock Ensemble II

EDIT (9/2/2011): Here is a copy of the SDR Presentation I did for my local ham club and used this FT-450+Softrock setup as a live demo. 

I have been playing with a Softrock SDR Ensemble II HF Receiver for a while and then I read about a european ham, who modded his FT-450 to work with his SDR (a Mercury SDR, not a Softrock), so I thought I might follow in his footsteps and do some experimenting as well.

The first thing I tried as duplicating the IF-tap that he had performed, it was fairly simple to do, just connecting a stereo cable up to a couple of pads on the RF board on the bottom of the radio and you can extract the I/Q signals from the built in quadrature detector(SDR) built inside the radio itself.

Here are the points on the board.

While it did 'work', it was quite disappointing to see only a few khz of bandwidth on the the display after having been spoiled using my Softrock to see 192khz wide bandwidth that usually covers most of an entire band in real time.

You can see the parts of the band that do escape the 10hkz roofing filter on the FT-450 IF in the SDR software here, you end up with a little signal on each side of the center point:

That was pretty sad looking compared to my Softrock in 192khz, look at the whole band goodness.   So, after that experiment, I moved on to trying to perform the "RF Tap", where you tap into the RF front end of the FT-450 to provide an RF out just after the passband filters, the preamp, and attenuator, and the transmit/receive switching inside the radio.  

This lets you share the same antenna with your SDR Receiver and your FT-450 continuously, and use the SDR as a sort of panadapter for your rig that has independent receivers.

This mod is also pretty easy, it involves bringing an antenna connection from inside the FT-450 to the outside to feed into the FT-450.  

When you pull the bottom board out of the FT-450, you will see that there is quite a bit of room inside there for cooling fins and airflow, and this makes it pretty easy to put in the ultra thin coax run to a jack on the back.

You can see all the room in there in this photo:

The connection points for the coax are on the bottom board that normally covers that space, so its a simple matter of soldering the coax leads to the correct points on that board, running the coax in the corner and under the board into this big space, and to the back of the radio.

Here is where you can see the points to connect the coax leads:

The coax is connected to the leg(that you can't see) on that inductor to the top left next to the finger.  

I made a little strip of copper to solder to the metal shield box that I could lay the coax into, let it provide some stability and strain relief for the cable, and solder the coax shield to as well.  The center conductor of the coax is soldered to the top left pin on the inductor.

Here is a photo(sorry, its a little fuzzy) of what it looked like after the coax was soldered to the board.

I then ran that coax down in the crack between the case and the board, to the open area underneath where I put in a SMA Connector into one of the cooling slots on the back.  The slots are nearly big enough and barely needed any drilling to make the SMA connector go through.    BTW, I put my board into a computer static bag, sealed as best I could, and then used a powerful shop vac to make sure that any stray metal pieces were not going to be loose inside the radio after using the drill on the aluminum rear panel.

Here is the SMA connector:

The Softrock radios, have a pretty strong signal that they leak back down the antenna and that would NOT be a good idea to leak signal into the beginning of the receiver IF Stage in the FT-450.   So, I used a buffer amp to put between the FT-450 and the softrock to eliminate that possibility.  A buffer amp creates a one-way only RF connection and does not allow any signal to leak back up to the FT-450.  It also provides a little bit of pre-amplification as well.  I choose to use one of the popular Clifton Laboratories Z10000 buffer amps, that is used by many people interfacing Softrocks with various types of radios.

This photo shows my finished setup, FT-450 SMA-BNC -> connected to the Buffer Amp -> connected to the Softrock.

With this setup, I can now get the full 192khz bandwidth use out of my Softrock, use is as an independent receiver, while sharing the single antenna, getting automatic T/R switching, and still take advantage of the front end preamp(IPO), attenuator, and extra bandpass filtering inside the FT-450 front end.  

This is much better than when I was using the Softrock before, I had to either disconnect the FT-450, or use another no so good antenna for receive only.  Being able to have both radios connected to my 80M OCF full-time has made the Softrock receiver a very important part of my radio setup and working right alongside my FT-450.

There just is no comparison between the 10khz output of the FT-450 internal IF, vs using the full 192khz of the Softrock.

Its quite a setup that complements my FT-450 for just only the $74 for the Softrock Ensemble II HF Reciever, and the $25 Z10000 buffer amp.  


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