Wednesday, December 8, 2010

Software Defined Radio - What Is It

Over the past year or so, I have made mention of the SDR (Software Defined Radio) in some facebook posts.  I get questions from time to time, so I thought I would write a little bit about how this works and what it is, exactly.

I have 2 different SDR's actually.  One is a receiver only, the other is a transmitter / receiver.  Both of my radios cover the HF (shortwave) bands, from 1.6 - 30 MHz.  The radios are kits, yea, you have to build them.  They are a PC board which you have to populate the board with the parts.  You supply the case for it, but the newest versions supplies all of the connectors.

The finished radios - Softrocks have no knobs, no volume control, no tuning dial, nothing.  It is a black box with an antenna connector, a USB port, and 1 or 2 audio connectors, depending on if your board is receive only or is a transceiver and a power connector.

The USB port is used to tune the radio.  The software which you use with this board sends tuning code to the board via the USB.  It also  automatically selects the band filters for the frequency youre dialed to.

The audio connector on the board sends a stereo audio frequency signal to the sound card.  This signal is audio, but there is a slight phase difference between channels that is derived by the mixer on the board.  Actually, there are 2 mixers on the board, with a common local oscillator , however, one mixer is fed a phase delayed signal from the local oscillator (90 degrees).  The outputs of the 2 mixers therefore has a slight phase shift in the mixed down signals.

In transmitting, the transmitter basically reverses the above process, amplified and transmitted to about 1 watt, which I feed into a small linear amplifier outboard.

Because of this special stereo audio, the DSP chip in your sound card and the associated software is able to distinguish between upper sideband, lower sideband, AM, narrow band FM, double sideband (with or without carrier), DRM...anything you might want to receive.

The software (there are several different programs available) displays the entire spectrum that the soundcard sample rate allows.  For instance, if your sound card is capable of a 96 Kbps sample rate, you are able to see 96KHz of spectrum at one time on your display.  Lets say you are looking at the 49 meter shortwave band at night, you will see a spectrum analyzer display that is just under 100 KHz wide, and you will see every station within that bandwidth on the display.  The software is calibrated in dBm, and you can see which signals are stronger or weaker and what frequency theyre on.  A simple mouse click will allow you to select any signal that you can see.  The demodulated output appears at your line output of your sound card.

One of the biggest features of this technology is the filtering.  By "grabbing" and dragging the audio passband window in the software, you can continuously vary the bandpass and center frequency of the filter so you can eliminate annoying heterodynes and other interference from the sighal you want to actually listen to.  There are preset filters, which vary from 2.4 KHz to 16 KHz in the AM mode (there are other filters for SSB).  One can select one of these filters and modify them any way you want to enhance the intelligibility if the signal you want to hear.

Synchronous detection on AM is available in some programs that allow you to listen to shortwave stations in the presents of "selective fading"  Selective fading is a phenomenon where the carrier fades, but the sidebands arent faded.  This causes severe distortion during the fade, but the synchronous detector eliminates that problem by injecting a phase locked BFO to the carrier frequency, simulating the original carrier, and since the BFO does not fade, you will never know there was a selective fade going on (unless you look at the display).

All of these features are in the software.  The hardware part is just a mixer and oscillator that produces an audio baseband signal for which the software can do its work.  The hardware end of it is extremely simple.  There are receivers available for as little as $20.  The all band  receivers are about $50 or so.  When these are used with a good quiet sound card, the performance is quite unbelieveable.

I hope this answers a lot of questions as to what this technology is about.  This is a basic, non-technical explanation.  There are more in-depth websites that describe the technology in far greater detail.

Saturday, November 13, 2010

2304 Yagi

Being I got some power out of the transmitter, I had an idea a couple of days ago, and thought about building a yagi antenna for 2304.

I went with the DL6WU design, but with a twist.  Instead of doing the folded dipole and balun, I went instead with the WA5VJB unbalanced half - folded driven element.  Everything else about the yagi is in accordance to DL6WU's calculations.

I have 10 elements built so far.  The longest element is about 60 mm long, and the boom length is 12 inches (305 mm).  The entire antenna is made from hobby brass, the boom is 1/4 inch square brass.  The elements are 1/16 inch diameter brass rod.

Here is a photo of the driven element.  The driven element is insulated from the boom. At first I could not get the SWR down on the driven element.  Some adjusting of the driven element length, shape and spacing to the first director, I got the return loss down to -30 dB or more.  I cannot measure below that level of reflected.

As you can see, the antenna is quite small.  The antenna appears to have decent directivity.  Although I have not yet completely tested it with a weak signal source, placing my hand in front of the antenna causes wild fluctuations in the reflected power, but moving my hand around the sides and to the rear of the antenna shows very little change in reflected power.  This kind of tells me that the RF is being radiated off the front of the antenna, which is what we are looking for.

The antenna will be extended to about 2 feet.  I wanted to try to see if I could make this work with 10 elements before I waste the additional brass (and time) with a longer antenna.

I used the VK5DJ Yagi Calculator program to design this antenna.  The driven element was designed by me, using the principle that WA5VJB used on his 1296 & lower antenna.  The length was arrived at empirically, trimming the length and spacing between the DE and 1D.  The odd shape of the hairpin does not seem to affect anything, its just how I happened to bend the DE.

I still need to package up the transverter and actually finish it.  The antenna experiment was a little bit of a distraction to break some of the monotony of the rest of the project, besides, I had some ideas after talking to N6NB, Wayne at the Packrats VHF conference regarding his Quagi design.  Since his designs were done on an antenna range, with a limited number of elements, I posed the question "How do you think your principles would work on a long boom design, such as the DL6WU design - using his director calculations, but replacing the reflector and driven element with your quad elements".  His reply was that it should work.  Although I did not go with the quad elements on this design, I  did think that the WA5VJB driven element should work with this antenna, which apparently it does.

Monday, November 8, 2010

2304 MHz Transverter - Photos

As I promised, here are some photos of the nearly completed 2304 rig.

 This is the complete rig

 One of the modified RF amplifiers with the cover off.

 The other amplifier.

 Mixer and IF Attenuator

 Bandpass filter

 Unused amplifier module.
Modified MMDS unit.

So these are the pictures of how this thing looks right now.  The amplifiers are not bolted down to the aluminum panel yet.  I have yet to install a T/R switch and I need to come up with some kind of power distribution.  This unit takes +20V, -20V and +12V to make it all work.

Sunday, November 7, 2010

2304 MHz Transverter - Its almost done!

I know I promised a posting describing the filter and other modules that I'm using in this project, but I thought I would wait until I had gotten some of it actually working.  Since I am now getting a useable amount of power out, I felt it was time to write a little.  Today I built an IF attenuator to drop the 144 MHz IF level from 250 mW down to 1 mW to feed the mixer.

I then started hooking up the modules that I had built up.  The LO was fed through a commercial low level amplifier module that was part of an amplifier chain which I will describe in a couple of paragraphs down this entry.  Measured LO was about +16 dBm.  The mixer wants between +10 and +20 dBm, so this level is perfect.  From there, the output goes into the LO port of the mixer.  The IF port goes to the 24 dB attenuator that I just built, and from there goes to the FT-817.

The RF port is connected to the band pass filter.  This is a 3 pole inline resonator filter that had to be modified slightly to get it to tune 2.4 GHz.  This filter does have a cool feature that is worth talking about.  It has 2 notch filters incorporated in it.  I tuned one notch to the LO frequency, the other to the image.  This should be one clean transverter!  The LO and image look to be down better than 80 dB because of these notch filters.  The tuning of the bandpass filter is quite sharp as well.

From the band pass filter, the RF goes through my 2- mmic preamp I built from Down East.  I'm only seeing about 20 dB of gain, however, so I'm not sure if there is a problem or not.  I'm getting 0 dBm out of the preamplifier.

WA3TTS gave me some surplus 1.85 - 2 GHz hardware, including a filter and an amplifier chain.  The amplifier chain consists of 5 modules.  I'm not certain how much input power is required to drive the entire chain to its rated 5 watts, but my guess is about a milliwatt or 2.  The modules all needed to be retuned to 2.4 GHz.  The modules are built one stage per module, and are built on ceramic circuit board material and have etched tuning and matching circuitry with no tuning adjustments.  The modules that I've tuned so far have been tuned with my Dremel tuning tool - carefully grind away printed capacitors and tuning lines.  This is opposite of most microwave commercial hardware, as most surplus is designed to operate above the amateur bands, such as the MMDS unit that I added material to its internal PC filters to get it to cover the ham band.  Because these units operate below the band, the opposite has to be done - copper has to be removed.  Because the copper is either vacuum deposited or etched on ceramic, an X-Acto knife was pretty much useless.  I then attempted grinding away the traces carefully with a fine grinding bit on the dremel tool.  With the unit powered up and the covers off the modules, I connected the power meter to the output of the first module through the attenuator, and applied drive from the IF.   I then began grinding the input network in the module while watching the power meter.  As the power came up, I continued until I saw no more increase.  I did the same with the output network.  I'm seeing about 10 dB of gain thru each of 2 modules I have done so far.  Currently I'm getting +23 dBm out of the last amplifier.

Well, thats where I am with the project right now.  I still have a 5 watt PA to tune.  All of the modules have to be mounted down to the chassis, and the T/R switching still has to be built.  The receiver is working, and the transmit is working at the 200 mW level, and the next thing I think I'm going to do is install the T/R relay and try to make a short range contact with what I have so far.  The 5 watt PA will be more difficult to tune, as it consists of a pair of devices which will have to be balanced somehow.  I'm not entirely certain how I'll retune it, but once I figure out a gameplan on tackling it, you can bet I'll be posting a procedure right here.  Check back soon for the info!

Sunday, October 31, 2010

2304 MHz Transverter - Significant Progress Made #1

Welcome back!  Today was a good day.  Got a LOT done on the transverter with the help of WA3TTS.  There was so much that we did, I can't write it all in one post, or in one night.  I'm going to split this up into several postings.  Question is, where to start.

First thing, and probably a very important thing is we checked the LO level and spectrum.  The level is much lower than I expected, I'm getting about -3dB at the SMA connector on the receiver brick.  The good news is it is VERY clean, all spurs are down by more than 60 dB, and the nearest spur is over 100 MHz away from the intended LO freq.  My plans have changed slightly because of this.  Since I have 2 of the Down East ERA2 2 stage amplifier boards.  I plan on taking the unbuilt board, and cut it in half, making 2 single mmic boards.  I will then use one of these boards to amplify the LO.  These boards should have about 15 dB of gain, so I should get about 12 dBm out of the amplifier, enough to properly drive the mixer.  I'm certain that if i fiddle with the LO probe, I could increase this level, but since the LO is so clean, I am almost tempted not to mess with it.  At least I know how much RF is there, it wont be difficult getting the level up to where it needs to be.

While I was there, I finished the mixer module.  We added a filter (more about this on the next post), and measured -20 dBm at the RF port of the mixer.  We only used the available -3dBm from the LO source.  A signal generator simulated the IF, tuned to 144 MHz.  The mixer output saturated at +6 dBm.  I believe that when I increase the LO level to +10 - +13 dBm, the output level will increase dramatically.

We did not test the 2 stage low power amplifier.  It is ironic to think however, that the -20 dBm coming out of the mixer matches perfectly the 2 stage gain of 30 dB, and in theory, I would end up with the +10 dBm that I'm shooting for at the output of this amplifier.  I believe it would be better, however to drive the LO to the +10  dBm level and run less IF energy into the mixer, thinking the linearity would probably be better coming out of the mixer.

As you can see from what is presented here, the rig is almost ready to hook to an antenna.  All that it needs is a good filter following the mixer, and perhaps a bit more power.  Tomorrow I'll write about a filter that we retuned and some of the really cool features of this filter.  We'll also talk a little bit about power amplification too.  I'll leave the cliffhanger here... Lets just say, I got a solid state power amplifier that will provide meaningful power for portable work.  It will need some work to get it to run on 2304, so will be experimenting with that soon also.

Stay tuned, keep the dish pointed this way, and check this frequency soon for the next update.  73 for now.

Thursday, October 28, 2010

2304 MHz Transverter - A Little Bit About the TX Mixer

While I'm waiting for the parts to come to repair the ABPM, I thought I'd write a little something about the mixer that I'll be using with this rig.  The mixer I'm going to use is an old Vari-L DBM-184 flatpack double balanced mixer.  The specs on this device, although it is a rather old device shows some promise according to the datasheet.  It will accept up to a +20 dBm LO, the LO to RF isolation is about 20 dB, and is good to 2500 MHz on the RF port.  The conversion loss is about 8 dB, which is typical for a DBM.  Its 3 dB compression point is +6 dBm, which I would assume is the output power, which corresponds to an IF drive level of +14 dBm when  used with a +20 dBm LO.  I will not be driving this device that hard though, figuring on driving the device with about 0 dBm, and between +10 - +13 dBm on the LO port.

I picked up 2 of these mixers at the 2010 Packrat (Mt. Airy VHF Club) VHF Conference.

I am in the process of packaging the mixer in a brass box, just slightly larger than the mixer itself (3/4 inch square), with SMA connectors connected to all 3 ports.  This will make the unit a "module" which is how I like to build things, especially when working with the microwave bands.  This method of construction allows one to substitute different components, so one can experiment to find the best performing module for this particular combination of parts.

Basically, the planned signal path will be something like this:
From the LO tap in the CalAmp RX converter, LO will be amplified using a MSA-0386 in a homebrew amplifier run at saturation, feeding the DBM-184 mixer.  The IF will be an attenuated 144 MHz TX signal from the FT-817nd, feeding 0 dBm into the IF port of the mixer.  The RF port will feed a 3 resonator BPF designed by G0ORY, details of which appear here.  From the filter, the RF will be amplified by the already constructed ERA-2 mmic amplifier.  From that point, I'm unsure as to what the final power output will be, but I am hoping I will find an amplifier that will provide a couple of watts on the band.  What I use will depend on what the pocketbook will allow, as well as what power supply I have available.

Once again, stay tuned, as work progresses, I will post again.

Saturday, October 23, 2010

2304 MHz Transverter - Transmitter Construction

After what seemed like forever, the ABPM (All Band Power Meter) arrived from Down East Microwave.  I had also ordered 2 ERA-2 amplifier boards at the same time.  I had the power meter built that evening, and went to test it, and the microwave detector does not work.  The parts in that section are extremely tiny, and I'm thinking I popped the detector chip.  I think it was probably my fault.  I also believe I'm losing my touch, as I'm having more difficulty working with surface mount parts due to their size.  I think I need to invest in one of those big magnifyers with the light in the head if I plan on continuing to work on this sort of thing.

Anyway, the power meter will read from about -20 dBm to +10 dBm in 2 bands - HF thru 500 MHz, and from 500 MHz to 10 GHz.  The low frequency sensor is working perfectly.  I got this shipment yesterday.

Today, I built one of the ERA2 dual mmic amplifiers.  I am going to use this as a transmit amplifier to get to the 10 milliwatt level.  10 milliwatts is a magic power level, as many higher power amplifiers are designed to input 10 milliwatts to get you from 1 watt to 100 watts, depending on what you are planning.

The ERA2 preamp boards are tiny as well, but I didnt have too much trouble building this one.  The 0805 chip caps are small, but fortunately, in these amplifiers, they're not too close together, and the circuit for a mmic amplifier is very simple.  These boards are nice high quality boards, made of Teflon, and have plated through via's.  These amplifiers provide about 30 dB of low level amplification, and will output up to 20 milliwatts at the 1 dB compression point.

This is a photo of the amplifier board.  As you can see, it is quite small.  Of course, I have no way to test it until I have the mixer finished.  I am currently working on that now, but I'm short one SMA connector to make that happen.

I still need to finish the mixer, and I also need to make a bandpass filter to place after the mixer that will pass 2304 MHz, but block the 2160 LO and 2016 MHz image.  I am going to use a 3-resonator type filter similar to the one I made for my 1296 rig.  Things start to get rather small on 2304 MHz, the resonators are less than an inch long on this band.  Its a good thing I have a micrometer.  I'll have the filter swept before I use it on the air.  If it's not selective enough, I'll use a cavity filter instead (or in addition to).  2304 is an awkward band in that it is more difficult to homebrew components such as the filters.  Cavities for 2304 are about 1 1/2 inches high, which makes them somewhat on the large size if you are trying to build small.  The resonator filters are less than an inch, and they require some level of precision for them to work well.

Once I get the mixer and filter built, I'll post again, and let you know how it all plays together.  Once I get to the 10 milliwatt level, I may attempt to make a contact on the rig if I can find someone with the capability to operate that band without having to drive too far.

Stay tuned, the next update will be coming soon!

Saturday, October 16, 2010

New Project - 2304 MHz Transverter - Tuning the Front End

OK, I got the ambition to hook it all up today and start tuning the receiver.  I used a very crude setup.  The only signal source I have that will generate a signal near 2304 MHz is the second harmonic of the local oscillator in my 1296 transverter.  I used that as the signal source.

I had to set up the signal source about 20 feet away from the workbench to keep the RF from being picked up directly on the 13 cm circuit board.  I put a homebrew 1/4 wavelength antenna on the input side of a 0 - 50 dB attenuator, then fed the other side of the attenuator into the RF in on the converter.  I used my FT-817 as the IF.  Tuned to USB, I easily spotted the signal very close to 144 MHz on the IF.  The signal was about an S-2 with 0 dB of attenuation inline with the little 3 cm long antenna.  I began snowflaking the hairpins, adding small strips of copper to the hairpins where I saw an increase in signal and soldered them in place.  There were a couple places that gave huge increases in gain, in the middle of the filter.  After about 2 hours work, I was able to get the signal up to about an S-7 with 20 dB of attenuation in line with the little whip antenna I was using as a pickup.

The frequency stability appeared to be quite good, there was some drift when I first powered it all up, but that quickly settled down after it was on for about 5 minutes or so.  I did not have to touch the VFO dial in the IF rig after  that time.

The next step will be in building the transmit side of the transverter.  I am still waiting on my order to come in from Down East- one of W1GHZ's power meters and a couple of MMIC low level amplifier boards.  I need the power meter in order to tune the TX filter which I have yet to build.

Oh, I'm using this article as a guide to my conversion:  No sense reinventing the wheel, being Adam already did the hard part.

Stay tuned, when I start on the TX portion, you can bet I'll talk about it here.

Thursday, October 14, 2010

New Project - 2304 MHz Transverter

Its been so long since I've posted in here, I almost forgot I had this blog site.  I haven't been very active since my last post, but I feel its time to document a new project that I just started today.  This is a major project for me.  What I'm doing is building up a transverter for 2304 MHz, partially from scratch, partly from an old MMDS receive converter.  I'm building this unit around the California Amplifier model 31732 MMDS downconverter.  These units were originally used to receive over the air cable television.  I have successfully retuned one for Amsat Oscar 51 (AO51) ham satellite S band downlink on 2401.200 MHz.  The converter is extremely sensitive and they appear to be stable enough to use as a basis for this project.  This is the first time I've attempted to build my own microwave rig from either converting surplus or scratchbuilt.

The design goal for this transverter is to build a portable 13 cm station.  Power output of a couple of watts, and later perhaps as much as 75 watts using converted surplus.  This band is easy to do this with, being there is a nice variety of surplus hardware that can be used on these frequencies.  The project will use the MMDS converter for the entire receive chain, including the LO.  A probe (first modification) is installed just above the LO filter striplines, and exits the chassis to an SMA connector to be used to drive the TX mixer.

The TX mixer, bandpass filter and low level transmit amplifier will be homebrew, external to the MMDS whitebox. A surplus double balanced diode ring mixer will be used as the transmit mixer.  From the RF port, a homebrew 3 resonator filter will pass only the LO + IF output of the mixer, then will be amplified to approximately +10 dBm, which will drive a commercial PA, which, depending on what I use, will run anywhere from 2 to 75 watts, depending on the model I'm able to acquire.

The first modification I have done was to install the TX LO probe to tap off some 2160 MHz energy to drive the TX mixer.  This involved milling down a lip  on the case of the converter and installing an SMA connector with a 30 mm probe inside the whitebox.

Today, I received the necessary crystal to change the frequency of the LO synthesizer to output the 2160 MHz.  The crystal frequency is calculated by taking the operating frequency (2304) minus the IF frequency (144), then dividing the result (2160) by 256 (8.4375).  This is the frequency of the crystal I ordered.  I ordered this crystal from International Crystal, and it came in today.  I installed the crystal, and checked the frequency, and it netted on frequency with very little effort.  The output from the probe seems to be enough to drive the TX mixer.

The next step will be in tuning the receiver printed circuit bandpass filter, lowering its frequency from 2500 MHz down to 2300 MHz.  My next post will describe the procedure, and will keep you informed as to my progress.  So until then, I'll have to wait until I get some RG59 and some connectors so I can hook up the IF rig to the unit and start adjusting the hairpins on the pc board.

Saturday, April 17, 2010

Cell Phone Interference on the Softrock Series SDR

Ever since I built my first Softrock, I was plagued by the usual buzz sound caused by a cell phone in close proximity to the radio.  It was so bad with the rig, that the phone could be anywhere within about 15 feet (or more) and the interference was still quite noticeable.  I had some success reducing it slightly by putting ferrites on the cables going to the radio, but could never reduce it to the point where it would not be annoying - until today.

The following modification should work on any of the Softrock sets, although I tested it on a TX/RX 6.3.

On an old scrap circuit board in my junk box, I found some molded RF chokes.  The particular value I found were 4.7 microhenries.  I installed one in series with the B+ line at the power jack in my shielded metal chassis thats holds the radio.  This reduced the interference substantially.  I then bonded the B-, shield of the serial connector and the grounds of the 2 audio connectors as well as the ground of the USB cable in my 6.3, and that reduced the interference to the point where I no longer hear the interference with the phone in my pocket, about 3 feet away from the unit.

I tried the inductor on the B- side of the power supply also, but when I did so, the interference came back to about the same level as it was before I began.

As an added bonus, by making this modification, I was able to also reduce the center "hump" substantially as well.  My analyzer screen in PowerSDR is now almost totally flat across the passband of the sound card.

If you have this type of interference on your V9 or 6.3, I strongly recommend doing this mod.  I assume the inductor value isn't critical, so long as the value is relatively small.  It seems that there is not enough capacitance between windings on the inductor I used to pass the 800 MHz garbage.

Saturday, March 6, 2010

Progress Made on 1296 Rig

Well, we figured out the problem with the 1296 rig, but I'm unsure how to fix the problem.  Apparently there has been no oscillation problem all along, the local oscillator chain is producing harmonics that are causing some strange mixing products.  We had a strong output on around 1250 mhz that was always at the output anytime the transverter was keyed.  This signal goes away when the oscillator is detuned so that it stops oscillating, but is always there anytime the oscillator is going.  The signal levels are equal to the desired 1296 signal when driven by the IF rig.  So when the rig is running, I had an output on 1296 and a carrier at 1250 (or thereabouts).  We traced the problem to a dirty LO chain. 

We were able to clean it up substantially by inserting a 3 pole BPF between the 10 mW transverter output and the next amplifier stage.  The correct way to fix this in my opinion would be to incorporate another of these filters in the output of the LO chain.  We didnt get that far with it today though.

When we hooked up the 2W PA, there was no output from the amp, and we didnt have time to troubleshoot it.  It was working when we began testing, so I am guessing it is something simple, such as a short in the RF path somewhere.  Since the TX is now clean, I can now troubleshoot the amp and try to maximise the output power.

Another possible problem with the dirty LO is that of receive performance.  With a dirty LO, the receiver will be receiving on 2 different frequencies, cutting the gain down by 3dB (or more) on the desired 1296 MHz, and also increasing the noise by 3 dB (or more),  I never really noticed a receive problem with the exception of the RF stage oscillating, which was a confirmed problem.  So, with that discovery, work can begin cleaning up the LO, and eventually I should get a 1296 rig on the air , hopefully before summer.

Wednesday, March 3, 2010

1296 Transverter Progress

For quite awhile, I have been battling a low power problem with an older circa 1995 Down East Microwave 1296-144 transverter.  At first I thought the PA was blown, I removed it and installed an outboard PA with no success.  Eventually I replaced the entire transmit chain with still no improvement.

Most recently, I replaced the mixer IC.  The original mixer chip is no longer made, however a newer model which spec's somewhat better than the original was installed.

I never reinstalled the PA module.  I am going to do some testing very soon with the +10dBm output from the driver.  If everything checks out, I'll continue to use the outboard 2W module, then feed that into the 30W PA.  Keeping the rig this way, in my opinion would be more versatile as far as making improvements and upgrades on the circuit.  Because everything is interconnected using UT-141 copper hardline, things such as bandpass filters and amplifier replacements can be more easily tried.

I am hoping to put the rig on a spectrum analyser and power meter to determine if the transverter is working properly.  If it is, I plan on operating some 1296 up on the Lake, as well as possibly some mountaintop operations this summer.  Stay tuned to my blog, I'll report here on the performance once I am able to make the proper tests.

Softrock 6.3 RXTX with USB Control

I ordered and built the USB I2C controller board for my Softrock 6.3 RXTX.  Adding this option opens up a whole new world for your Softrock.  Not only does it allow you to tune the entire bands, but also allows you to have general coverage receive capability with the rig.

It also allows external programs to take control of the radio.  This is REALLY cool, as you can run Powersdr in the background and use software such as fldigi and WSPR to actually control the frequency.  Fldigi logging works great too, as it can read the frequency of the radio and it puts that into the log automatically.

Another added feature is you no longer need the serial cable to key the transmitter.  This is all done now via the USB port.  Of course, you still need to set up virtual com ports so the additional software can communicate PTT to Powersdr. 

I have been using PowerSDR v. with this new setup.  This version has been designed for use with CURRENT firmware in your softrock, and it works quite well.  I find the audio is less choppy with this version as well, and it's a lot prettier on the screen with its customizable skins.

Upgrading your Softrock with this little $11 board is more than worth adding the option. 

On a sidenote, the other night I thought I would try some digital communications running barefoot 1 watt from the radio, and worked a fellow in Arkansas using Olivia 500/16 on 40 meters.  I was running 1 watt, he was running 40 watts and was using a Flex-5000.  We maintained contact for 1 1/2 hours, talking about SDR in general.  Was a real fun QSO.  I'm looking forward to working my first Softrock to Softrock rig, as I think that would be quite interesting.

Saturday, February 13, 2010

Softrock and the Digital Modes

Today I was experimenting with setting up PowerSDR-SR40 for use with fldigi and other digital software, and I got everything talking to each other.  When everything is working together, it makes operating digital so easy.  So far, I got PSDR working with fldigi and Ham Radio Deluxe.  I'm planning on getting it working with MMSSTV and EasyPal Digital SSTV program.  I dont think there will be any problems, as they should set up the same as the ones I already got working.

There are 2 programs you will need in order to make everything play nice.  First is "Virtual Audio Cable". it can be downloaded from here:

When you get it, you will need to create 2 virtual sound devices.  There are good instructions at the above website on doing this.  One will be needed for receive, the other for transmit.

The other program you will need, and you will only need it for software that also controls the radio, such as fldigi and Ham Radio Deluxe, and that is "com0com", This creates virtual com ports to link the control aspects together.  It can be gotten here:

You will need to create 1 pair of com ports for most applications.  There are excellent pdf directions on how to do this at the above website.

Then go into Powersdr and set up the "CAT" section.  Although some software will work using the identifier set for "SDR-1000", I've had better luck setting up emulating a TS-2000.  Under CAT control, set the com port as the lower com port number that you created in the virtual com ports, I used COM5. Fldigi will use COM6 under its CAT settings.  I used RIGCAT in Windows to control the SDR, and it plays nice.  I have had some problems getting the external programs to control PTT, so I just use VOX for that.  I used to use VOX in my Yaesu too when I ran digi modes.

To get audio to the programs, you need to set up virtual audio cable.  I used Virtual Audio Cable #1 for audio out from PSDR and VAC #2 for the TX input audio.  These settings will be found in the VAC tab in the audio settings in PSDR.  The audio settings in fldigi are just the opposite - VAC2 is the output device, and VAC 1 is the input.

Once everything is talking, fldigi will read the frequency of the radio and you can then use the logger in fldigi, and it works like any other radio would with CAT control.

Ham Radio Deluxe sets up in a similar fashion.

To listen to your receive audio, should you choose to do so, VAC has a little utility called an Audio Repeater.  You can set that up to input the proper VAC device as the input, and your soundcard that you use for your speaker audio as the output of the repeater.

There you have it, a basic overview as to how to set up different software so they will talk to eachother.  Once they talk, operation is a breeze.  I worked a little bit of the RTTY contest, and worked about 25 contacts in less than an hour with only 15 watts of TX power.

Good luck, and I hope this helps you get things working with your Software Defined Radio.

Tuesday, February 9, 2010

SoftRock v6.3 RXTX+Xtall

About 2 weeks ago, I finished building a SoftRock v6.3 RXTX+Xtall SDR transceiver.  I ordered the transceiver and  3 power amp, low pass TX filters, so I can cover 80 meters thru 10 meters.

The 6.3 TXRX is a 1 watt PEP transceiver capable of running whatever frequency bands that you supply PA's for.  The standard kit allows for 16 presettable (with a 4 section DIP switch) frequencies.  Each frequency is tunable over  a span of 96 KHz with the software, with the preset dip switch setting being the center of that tuning range.  All modes are possible, including SSB, AM, NB FM, and all of the digital modes, including Slow Scan Television using outboard software.

Most of my operation so far has been on WSPR on the 40 meter band, however I have operated SSB on 20 and 40 meters, and have worked a couple of countries using an outboard HFPack amplifier at about 15 watts.  The performance is nothing short of remarkable, and have gotten exceptional audio reports while using a VERY cheap computer microphone.

Operating an SDR transceiver requires the use of 2 different sound cards.  I use one card that works as the digital signal processor for the radio and the other to drive the speaker on receive and mic for transmit.  For the radio card, you want the best sound card you can get, with the lowest noise and highest sample rate.  92 khz sample rate cards are available with noise floors in excess of -100 dB, and they are common and inexpensive.  I bought a Soundblaster Audigy card for this purpose, but with many soundblaster internal cards, there is some phase shifting in the card, and I couldnt get a good balance without setting the phase and amplitude all over the place.  I've used an older USB card such as the Soundblaster Live external card and that works pretty well.  The external cards apparently do not suffer from the phase shifting that the internal cards do.

With the bare transceiver with the fixed frequency settings, the only software that is useable with it is a special version of PowerSDR, called;PowerSDR-SR40 and is available at  All other versions do not allow you to transmit if the fixed frequency is enabled.  There is, however an add on module that allows USB control of the Si570 oscillator that allows continuous tuning, which I ordered but have not received yet.

I will write more stories on this radio, and will detail a little more precisely on setting up this radio for use.  It is a fun little rig, and for roughly a $100 investment, you will have yourself a very capable little radio.

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