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Piggybacked on the other side of the DizDDS VFO is a direct conversion receiver made with a Universal Diode Ring Mixer kit and a LM386 Audio Amplifier kit.
I removed the diplexer and put in a .1mfd cap and a 51 ohm resistor to ground for the bottom leg and an FT-31-43 (20T of #28 wire) in series with a 22mfd cap to the IF output. I got this from the QRP Pops website. It's the one labeled 'C' under "Product Detector and Diplexers". I'm using Diz's DDS Development Kit with Bruce Hall's (W8BH) excellent software.
The Emtech ZM-2 serves to provide some front end filtering and actually allows me to go wherever I can tune the DDS. You can just as easily add one of the bandpass filters if you want the best performance for a single band. I don't really have an antenna for the lower frequencies but it still works pretty well. Over-all there is a surprising lack of hum and the audio is loud enough to drive earphones. I use it with computer speakers. This is a pretty simple setup that works surprisingly well!.
Here is a small audio clip (SSB)
And a little bit longer recording(SSB)
*I used a 10db pad(100, 75, 100 ohms) on the RX output connector of the DDS to get to +7dbm (about 1.5V p-p into 50 ohm load) for the LO port of the DRM
Last edited by ak2b (2011-01-07 13:49:38)
Both mixer and audio amp are mounted on a piece of PC board material and bolted onto the back of the DDS VFO.
You can see the Local oscillator output of the DDS at the upper right of the picture (which is the bottom back of the VFO). The output of the ZM-2 goes to the RF port and the IF port is plugged directly into the audio amp.
This is the diode ring mixer board.
And this is the LM386 audio amp board.
The audio sure sounds sweet -Diz
Tom, You never cease to amaze me.
Thanks for your nice comments, Ron.
I am going to try one of the TDA7052A audio amps that I got from Diz along with some preamplification and see if I can drive a speaker with it.
Here is a new addition to the DizDDS direct conversion receiver.
I added a project board with female headers so that I could plug in BPF boards. The one in the picture is a dual BPF boardbuilt for 20 and 17 meters. The pins on the generic board and the BPF board don't exactly line up so I plugged everything in to each other before I soldered any pins. The BPF headers were moved from the top to the bottom.
Here is a much better recording made without any filter, directly from the output of the LM386 amplifier.
Man Tom, That sounds better than my FT-817 !!!!!
How much bandwidth are you getting out of the K&P BPF's ?
I took this pic some time ago and wanted you to look at it for me.
I also needed a test pic loaded onto my website to see if I could link it to this post.
This was taken with my HP-3585A 40mhz SA.
It's been so long ago that my guess is that I did not have a load on the DDS.
Here should be the pic:
Last edited by W4DNQ (2011-01-14 15:00:03)
Thanks for the nice comments on the RX audio.
The dual BPF shown in the DC receiver was made for 20 and 17 meters and the plots for it using the N2PK vna are here. Diz mentions elsewhere that the dual board BPF is somewhat wider than the single board filter. Since you have a spectrum analyzer(hopefully with a tracking generator) you should be able to set up the dual board to cover the bands of choice; or at least the ones I plotted. I have only the one dual band board.
See this post by Diz.
As for the sa picture - nice to see you can now post pics. Are you looking directly out of the DDS into the SA? Do you have the pad resistors installed on the DDS board?
The only drawback to a great sounding DC receiver is that you hear the signal twice. Since I already had a FireFly I bought the audio signal processing board (ASP) for the R2pro and figured I would make a phasing receiver and get rid of one of the sidebands. After realizing that I had to bias the input to the ASP, I got it to work. So, I made a video to show off http://www.youtube.com/watch?v=-KJBLCpZ3ek
Well after reading about all the fun you are having, I'm getting off my butt and building something! I've got the DDS-60 working with an ATmega32 controller and I just placed an order with Mouser for the parts I need to build the R1 receiver from Aug '92 QST. I had to make some changes because the LM387 is now extinct. I'll sub a common dual jfet op-amp and add a pair of resistors to create a virtual ground to run it with a single rail supply. I have all of the transistors or equals in the junk box and a MCL mixer. I'm going to use a 7 pole 3khz butterworth LPF, I got the values from an on line design calculator. Since I later plan on using the R1 as the product detector in a superhet I don't need a brick wall audio LPF, but I wanted something a bit less wide than the 4khz 5 pole design in the QST article. I couldn't find a 500 ohm audio taper pot so I going to use a 1k pot in parallel with a 1k resistor. I'm not sure what that will do to the taper, but it should be close. Good thing I ordered now, a lot of the parts made in Japan (Panasonic caps) are becoming backordered for who knows how long!
I was toying with the idea of ordering the PCB from Far Circuits for the R1, but since it's all audio anyway I'll just breadboard it on a perfboard. I'm making some changes to the circuit anyway (due to subbing out the '387) and I don't need the mute fet. I also have an AD9954 based DDS in the works (I ordered a chip 340mhz oscillator for that as well as the parts for a 100mhz LPF). I'll stick with the DDS-60 for now, but I'm curious to see if the '9954 will have less spurs.
I'll probably test the circuit out on 20 meters first with a simple front end, then order the PA3AKE toroid kit from 'DIZ to make it an all bander. I've got a nice cabinet to house the project in (I hope to eventually end up with a complete HF SSB transceiver) that I found on Canal Street NYC (Leed's Radio) back in the '70's when I was in college.
I see there are a few versions of the R1 - which seems to have evolved along the way to the R2. I am very interested in seeing the outcome of your project. Please post pics, etc.
The meter used in my icon is from Leed's on Canal Street, also from the 70's. I used to take the subway every Saturday morning and hang around down there. .
I see there are a few versions of the R1 - which seems to have evolved along the way to the R2. I am very interested in seeing the outcome of your project. Please post pics, etc. The meter used in my icon is from Leed's on Canal Street, also from the 70's. I used to take the subway every Saturday morning and hang around down there. .
Leed's is now in Brooklyn. I used to work at Ramco Electronics on Canal Street in the early 70's. I also worked one summer at Arrow Audio on Chambers Street.
The R1 has been used as the product detector / af stage in a few receiver/transceiver homebrew designs following an IF strip. I have about half a dozen surplus 9mhz filters that were made for the Clegg Sidewinder transceiver. They have a BW of about 3.1khz, but they are eight pole filters with skirt walls a gazillion db high so they might have the ultimate rejection of a much narrower filter. (Especially if I cascade three of them in the IF strip!). I got them at Dayton in '92. I'm not sure yet what I will do for the IF strip of the superhet receiver that will come later, but I do have about two dozen CA3028A IC's (bought them from Jameco on sellout a few years back). At this point, there is SO much crap in my Junquebox after two score years of collecting that I HAVE to put SOME of it to use!
One idea I have to yet code in the DDS controller is for an alignment generator using the A/D channel and an AD8307 log detector chip. I can program the DDS to sweep and read the output of a filter (BP, LP, xtal, etc) and collect the data on the PC. I think I can call functions in GnuPlot to graph the results. This way I can align the PA3AKE BP filters in the front end.
I'll post some pix on my website at www.scharkalvin.weebly.com later.
Here is a photo of my DDS-60 controller. The DDS-60 is in the metal box in the upper left hand corner. The box contains an MCL power splitter so the DDS can drive both a receiving and transmitting mixer without switching. The probe is connected to a frequency counter. Between the DDS-60 and the LCD is a small speaker that is used to generate a 'beep' whenever a key is pressed on the keypad. The circuit below the LCD is a constant current regulator to power the LCD LED back light. I know it's a tad overkill as a simple resistor would work, but this allows me to adjust the light level. The controller itself is an Atmel atmega32 on a simple prototyping board I found on ebay. You can barely see the rotary encoder and knob at the bottom of the picture. The keypad shares all of the lines used to interface the LCD.
Last edited by wa2mze (2011-03-29 20:29:27)
My parts order from Mouser arrived on Friday. As usual I managed to screw something up, an 82nh inductor ended up as .82uh. My fault navigating the website. Only a $2 mistake. I can live without it for now, I'll get to the AD9954 DDS later.
I downloaded the freeware version of Eagle Cad and started playing around with it. I still have a lot to figure out, but I did capture the R1 schematic from the mixer up to the volume control. I'll make the amplifier portion on a separate circuit sheet (and a separate PC board). It took awhile to layout the parts to fit on a single sided board 2.25" x 3.375" without any jumpers. (I did have to squeeze a trace between the emitter and collector pads of a triangular transistor pattern). I was also able to figure out how to print only the pads and bottom side artwork onto a piece of 'press-n-peel blue' toner transfer paper. The board is now etched and ready to drill out.
Eagle isn't a bad PC cad package. The free version limits you to boards 80mm x 100mm with two layers for conductors. It's free only if you don't sell your designs, otherwise it costs $49. The catch is that if you need larger boards (160mm x 100mm) and 6 layers the cost for the full package goes up to $747! ($498 if you can live without the autorouter). I tried the autorouter out, but I ended up routing my simple board by hand. If you are going to make PC boards about the same size as most of DIZ's kits the $49 package will serve you well. Oh and they have versions for Windows, Mac, and Linux! (I'm using the Linux version).
Here are the Eaglecad files for the R1 receiver PC board I laid out. This board only contains the product detector, diplexor and low pass filter.
The audio amplifier will be on a separate PC board
The file names are actually r2a.brd and r2a.sch. I had a 'brainfart' and called the project r2 instead of r1 when I created the Eaglecad project (well I screwed up my first attempt while learning eagle and started over).
Last edited by wa2mze (2011-04-07 09:51:28)