delara news Delaware Amateur Radio Association, Delaware OH   VOL 36 NUMBER 8

Joe Fischer

AA8TA

The SDR Bandwagon

Well, gee, all the cool kids have a panadapter, or band scope, so why not me?  I’m pretty happy with my Kenwood TS-590S, so it is a little hard to justify getting a fancier rig just to get a band scope.  But, what if I could add one? One way of doing that is to use an SDR (software defined radio).  So, I picked up this: I would like this to “hear” the same signal as my radio.  If I had a TS-590SG, that would be super easy; hook the SDRplay up to an RCA jack on the back, change a menu setting and start playing (like that play on words?).  But, my S-model does not work that way, so a little more tinkering is involved. Fortunately, there is a jumper inside the radio that controls an attenuation setting, I assume for the broadcast band.  The RF to the receiver goes through this and is muted during transmit.  Also allows one to pick up the receive signal before the roofing filters and the dual IF circuitry later on. Here is the rig all ready for a little bit of surgery; this won’t hurt a bit: Kind of hard to see, but there is a jumper next to the right side just above one of the cover screw holes.  Now we need a suitable shorting block to pick off the signal.  I wanted the jumper shorted otherwise 20 dB of attenuation would be introduced.  An old computer had a wiring harness with a 4 or 5 pin header that would work so it was re-purposed. This was soldered onto one end of a piece of RG316 that just barely fits through a gap on the rig’s bottom cover.  One end of the RG316 jumper was cut off (hey, sacrifices have to be made) and we have this: I drew an arrow on the cover to make sure I got the cable in the right place.  I don’t want to be the doctor that removes the wrong kidney because he neglected to mark which side of the patient to operate on. Next, we insert our new jumper: The ground braid is soldered to a ring lug that is screwed to a convenient hold-down screw. And, the patient is all buttoned up and ready to return to action (no pain meds needed): The nice thing about this is that this can be easily undone; no holes were drilled and nothing was soldered to the radio.  I taped the original shorting jumper to the inside of the bottom cover because I know I’ll never remember where I put it otherwise. The radio was put back in place (not that easy), cables were hooked up, power was applied and noise was heard in the headphones – whew!  Everything works. Here we see the action on 40 meters during the IARU contest on July 8 and 9: This is adjusted to show the range from about 7000 kHz to 7060 kHz.  The numbers in the upper right don’t mean anything.  I think that I need to adjust the sensitivity because the band was packed.  I also have to get used all of this.  By the way, the software is called CubicSDR which runs on my MacMini. One thing that is missing from all of this is the ability to click on a signal on the scope and have the rig go to that frequency.  Other people have made that work but I’m not quite so lazy that I need that feature.  Well, I’m pretty lazy, but not motivated enough to do the extra stuff needed to make that work – this was enough.  Besides, I’m not sure if that would work on a Mac. Look at me now – I’m a cool kid! Those of you who are the caring, sensitive types will be happy to know that no radios were harmed in the production of this document.
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