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Author Topic: SDR made easy on the cheap  (Read 4346 times)
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WA1GFZ
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« on: January 10, 2006, 10:04:06 AM »

A friend who bought a RA6830 asked if we could build an SDR interface that would plug into the radio. I found a little board that was called the soft rock 40 that is no longer produced. It sold for about $25 and covered a small portion of 40 meters.
This design can be duplicated and with minor changes be made to interface any radio with a 455 KHz IF. The crystal would be replaced with a color burst rock and the unused portion of a 74HC74 wired for an additional divide by 2. This would produce a 8.44 khz if input to a sound card allowing a DSP  bandwidth up to 16 or so KHz.
Imagine an R390A interfaced to your computer showing a spectrum display with sync AM detection and variable bandwidth adjustable with a click and drag of a mouse.
I have 4 or 5 different free software packages and looks like the hardware can be built for under $40.  The soft rock guys have a new kit that is a bit more money but I have not seen the schematic yet to see if it can be converted. I'll be glad to share schematics with anyone who wants to play with this stuff.  My friend is going to make boards for us but if anyone wants to produce some volume again I would be glad to help. This is cool stuff and having the option of DSP demodulation at the turn of a volume control is cool to have. I find the DSP does a little better job when conditions are poor. The spectrum display is very cool. The monitor bandwidth depends on the sample rate of the sound card but a stock card will easily monitor 24 KHz wide.  gfz
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KA8WTK
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« Reply #1 on: January 10, 2006, 07:04:49 PM »

The new SoftRock is indeed a cool little piece. For the schematic look at  http://www.hamsdr.com/Home.aspx and go to the "Downloads" area under "Public Download Directory" and sort for the SoftRock documents.

Mine took about 8 hours to build, start to play. I mounted my own SMT devices and wound the toroid coils. I am presently using Rocky software with the radio and am learning how to use PowerSDR with it. This thing is fun!

Bill

Pictures to follow. My web cam won't focus that close!
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Bill KA8WTK
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« Reply #2 on: January 10, 2006, 10:58:00 PM »

A friend who bought a RA6830 asked if we could build an SDR interface that would plug into the radio. I found a little board that was called the soft rock 40 that is no longer produced. It sold for about $25 and covered a small portion of 40 meters.
This design can be duplicated and with minor changes be made to interface any radio with a 455 KHz IF. The crystal would be replaced with a color burst rock and the unused portion of a 74HC74 wired for an additional divide by 2. This would produce a 8.44 khz if input to a sound card allowing a DSP  bandwidth up to 16 or so KHz.
Imagine an R390A interfaced to your computer showing a spectrum display with sync AM detection and variable bandwidth adjustable with a click and drag of a mouse.
I have 4 or 5 different free software packages and looks like the hardware can be built for under $40.  The soft rock guys have a new kit that is a bit more money but I have not seen the schematic yet to see if it can be converted. I'll be glad to share schematics with anyone who wants to play with this stuff.  My friend is going to make boards for us but if anyone wants to produce some volume again I would be glad to help. This is cool stuff and having the option of DSP demodulation at the turn of a volume control is cool to have. I find the DSP does a little better job when conditions are poor. The spectrum display is very cool. The monitor bandwidth depends on the sample rate of the sound card but a stock card will easily monitor 24 KHz wide.  gfz

Neat stuff Frank...might be interested..I need to come up with a better receiver in the shack and i had thoughts of building my own receiver. This might be a cool alternative.

Brent W1IA
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WA1GFZ
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« Reply #3 on: January 11, 2006, 08:56:15 AM »

The problem with most modern rice boxes is the DDS LO. A DDS is a crap generator and you just can't get maximum performance with a crap lo. The R390A is just about the cleanest LO. Hanging a SDR off it would be cool. The problem with the R390A is the 6C4 mixers.
I'm trying to come up with an SDR interface that can be built for under $50 including a pc board. Rocky software is cool I like the display. I like the performance of I2PHD software better though. His display is not quite as sharp but latest rev is pretty close to rocky. I2PHD has a nice AM sync detector that works much better than a sherwood SD3.
I just got Flex software working and plan to do some testing. It is similar to I2PHD with variable bandwidth.
You can't claim 100 dB of dynamic range if your lo makes a lot of noise.
The RA6830 phase noise falls below -100 dB at about 8 KHz off center meaning 100 db of dynamic range at 10 KHz spacing is possible.
You can't claim 100 dB of dynamic range if your IF filters fall apart at - 60 dB.
It took 3 sets of filters in my hot rod to get better than 100 dB of stop band.
Then it takes a crap load of shielding to isolate circuits.
SDR is just the icing on the cake. The trick will be to use enough hardware from a good radio to actually make a better system.
It is very cool that these software guys share the cool demodulation software for free!
BTW My TCI 8174 seems to be the best SDR demodulation but the bandwidth is limited to 6 KHz. The analog hardware is very similar to the cubic R3030 with a digital AGC. I would love to get my hands on th esource code for that radio. Then get the hardware for the second DSP that does spectrum display and I/Q output.
FFT Spectrum dislay is very cool. fc
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KA8WTK
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« Reply #4 on: January 11, 2006, 07:00:05 PM »

This is the SoftRock v5.o..... The two boards stack on each other..see next post...


* 3.jpg (26.78 KB, 320x240 - viewed 216 times.)
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Bill KA8WTK
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« Reply #5 on: January 11, 2006, 07:01:41 PM »

The bottom of the QSD board...whole unit not any bigger than a 9vt battery!


* 2.jpg (23.69 KB, 320x240 - viewed 221 times.)
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Bill KA8WTK
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« Reply #6 on: January 11, 2006, 07:03:26 PM »

Whole unit stacked up and ready to go! They have already sold 750 kits and are sold out for now.
Hope the pictures look "OK"

Bill


* 1.jpg (20.03 KB, 320x240 - viewed 220 times.)
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Bill KA8WTK
WA1GFZ
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« Reply #7 on: January 11, 2006, 09:42:38 PM »

Cool pictures. I want to build something to interface to a 455 KHz IF allowing the rest of the radio to act normal with the addition of SDR modulation. A friend and I will make the first units able to plug into a RA6830 A8 slot. This will allow stock demodulation or SDR or both at the turn of a volume control 
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ka0pad
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« Reply #8 on: January 11, 2006, 11:03:07 PM »

I've got a softrock40 tapped into the IF of my ts-430s, pretty nice to have the spectrum up on the monitor, and the AM out of my sound card and speakers is really nice, the ts430 sounds like crap. I've got another one here and plan to tap into my sp-600's If, just need the time to  do it, maybe this weekend. Might do my ft-102 after that.
It's been pretty frustrating for me because I'm a linux bigot, cant bring myself to touch windows except when I have to maintain the wife and daughters machine and I hate that. Just recently a couple linux gui's have appeared. I havnt been able to get John Melton's java gui to talk to the fifo's on my system, but am hopefull Edson's will work out. These guys have been over-generous with thier code. There are a couple yahoo groups active for all of this.
The newer softrock can be adjusted to any IF, just like the old one. The oscilator runs at the desired target freq, not x4 like the first one.

Fun stuff.

Larry

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WA1GFZ
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« Reply #9 on: January 12, 2006, 08:16:49 AM »

Very Good Larry,
That is what we plan to do. The spare 74HC74 will be pressed into service. This will allow a color burst crystal frequency giving a 8.44 KHz IF off the 455 HKz. The circuit will work with almost any other IF. I'm actually considering a Hot rod model off my 40.455 MHz iF with high dynamic range parts. This would eliminate the second IF.
It will take higher dynamic range parts to get full performance. I was thinking of using a pair of double balanced mixers. I have tried a number of software packages and love the spectrum display and variable bandwidth. The Sync detector for am is cool
with I2PHD the best with the phase meter.  fc
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Steve - WB3HUZ
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« Reply #10 on: January 12, 2006, 09:43:37 PM »

I trust you've heard of Gnu Radio. It runs on Linux. Seems to be a little short in the amateur radio capabilities though. I guess there room to do some coding.

http://www.gnu.org/software/gnuradio/
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WA1GFZ
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« Reply #11 on: January 13, 2006, 08:49:53 AM »

Good point Steve. The problem with some software packages like Flex is bill gates needs about 30 meg of your hard drive to allow it to function. This is the only thing I worry about playing SDR. My drafting friend will be ready to lay track in a few days so I need to finalize the design. It looks like the SR40 oscillator chain and Flex Tayloe  with a mux from a different source provide the best performance for the least number of components. He has the board with the connector mounted so it is time for the hardware puke to release the design. I'm hoping he wants to sell some boards for others to play with the interface is a 96 pin 3 row DIN connector with SMB RF connectors. Output will be 1/8 stereo connector. Real easy to use anywhere. fc
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WA1GFZ
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« Reply #12 on: January 14, 2006, 10:56:54 PM »

GFZSDR design has beed submitted to drafting. The mixer comes form Flex Youngblood first article. I modified it from single balanced tayloe to double balanced.
I found a Fairchild mux pin for pin to replace the IDT part. Then I took the Soft Rock 40 oscillator circuit and added a 74AC74 divider section. Then added a couple caps to bypass the juice and it is a wrap. The plan is to plug the board into the RA6830 with a 1/8 inch stereo jack on the back. I'm sure it will be pretty cheap parts and maybe
we can provide some pc boards if anyone is interested. The plan is to be able to modify it to work on any IF and there will be 1 spare divide by 2 if a lower IF is the interface. The power interface is a cheap VME 96 pin DIN connector used in the Racal
and could be elininated or mated. more to come. fc
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Steve - WB3HUZ
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« Reply #13 on: January 14, 2006, 11:14:30 PM »

Nice. Wish I had a Racal.
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ka0pad
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« Reply #14 on: January 14, 2006, 11:39:48 PM »

Frank,

I'll take one if you have extra's. Please let me know.

Larry
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WA1GFZ
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« Reply #15 on: January 15, 2006, 11:52:08 AM »

Steve,
You do not need a Racal. It will work with any 455 KHz. IF. I'm putting a set of pads for an attenuator pad to set the level and 50 ohm input. The Racal puts out about -12 DBM. This converter will interface to an antenna with an input filter. It can be a stand alone SDR receiver with a 4X LO. The goal was to make it universal. I will try to see if we can do some boards if there is enough interest. My drafting friend has his own doard process and I don't know how many he is interested in making. I'm hoping we could make a file express pcb could work with. I also provisioned for an additional divide by 2 if a lower IF is the interface. This would also require a crystal change.
The power required will be plus and minus 12 to 15 vdc. It could be converted to single ended. fc
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WA1GFZ
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« Reply #16 on: January 15, 2006, 03:10:25 PM »

first round of schematic review complete. This guy is on a roll.
Components 1 transistor, 3 didital IC, 1 comparator, 2 op amps, 1 voltage regulator
and a hnadfull of small parts. should be cheap to build. now if we can produce a cheap board. I asked if we could do express pcb if there is enough interest and the price is right.  gfz
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Steve - WB3HUZ
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« Reply #17 on: January 15, 2006, 06:01:12 PM »

Ah, cool. So I could interface it with my SP-600. The 51J has a 500k IF, so a crapstal change would be needed. If you plan to build these, put me down for one.
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WA1GFZ
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« Reply #18 on: January 15, 2006, 11:38:14 PM »

Larry,
I asked my drafting contact to consider using a system that could talk with express pcb. This way we could do a production run if there is enough interest. There are no odd ball parts but I think he is going to do surface mount parts. I told him that was his choice. Us Hams are a bunch of cheap asses so I have no desire to make this a big deal. I would only like to share the hard part being the board.
My drafting guy is only set up to do a few boards and he has a real business designing custom houses.  fc
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ka0pad
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« Reply #19 on: January 16, 2006, 09:41:31 AM »

Hi Frank,

That sounds good, I can gather parts, the pcba is the tough one. Let me know if chipping in ahead of time would make sense.

Larry
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WA1GFZ
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« Reply #20 on: January 16, 2006, 10:58:00 AM »

Express PCB 2.5 by 3.8 inches which should fit  3 pcs for $51.
I will see if my friend can do that. fc
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