Multi-Freq Single SDR Digi-Monitor

So this was just a convenient place to post some detail about my present SDR setup  for a friend of mine.  Sorry for the lack of wordy detail :-)

Airspy, Spyverter, Hermes, and HackRF Using Leo Bodnar GPSDO

Leo Bodnar has developed a VERY NICE Clock Reference (I would call a GPSDO) which I recently purchased from Force12Inc they sell two of them this one, and this one (with a custom low phase noise xtal).

The Airspy SDR accepts a 10 MHz clock input.  I've been using mine until recently in a modified manner where I used the ADC1 direct input (which bypasses the on board filters, and AGC) to input the 9 MHz IF output from my Yaesu FTDX-5000.  I didn't really like this method since it bypassed some important areas when there are strong signals on 50 MHz.  It would frequently overload the Airspy (which I love btw), so I have a 30dB step attenuator in line to help control this easily.

Anyway, now that the Spyverter is available, (and it's a VERY VERY nice upconverter) I wanted to try to go back to a more standard method of getting the 9 MHz IF out into the Airspy.  Unfortunately the Spyverter (even the TCXO version) suffers (slightly) from xtal drift.  I discovered this immediately as this was the reason I had abandoned use of upconverters in the past.

I emailed Youssef from Spyverter asking him if he was aware of a work around for the drift issue.  I'm 99.9% of the time a CW operator, and this drift means that I'll be close, but NOT ON when I click on a CW signal in HDSDR.  Depending on the drift of the moment.

He mentioned that they had tested removing the xtal on board, and feeding 120 Mhz clock from a Leo Bodnar Clock Reference into it instead.  Leo's nifty little reference has the ability to create TWO output clock references at the same time from one GPS antenna connected to it.  I had it working providing 120 MHz and 10 MHz output within about 5 minutes after it arrived in the post today.

It took me about an hour (CAREFULLY) removing the on board xtal on the Spyverter.  I really don't recommend doing this the way I did it.  In fact if you plan to do something like this I'd recommend contacting the airpsy/spyverter folks and ask them for a board with no xtal on it at all.  It's NOT EASY, and in fact I feel lucky to have managed to get it removed without damaging the board or components.  I suppose if I'd had a SMT de-solder station it would have been simple.  But I don't.

Here are some photo's of how I accomplished this in my setup:

Right side SMA is the new one I added

After this is all done it's ready to test.  I attached the 120 MHz reference line from the GPSDO to the new SMA port on the Spyverter, and connected everything else up normally.

When I was done, I started up HDSDR and discovered that when I went to calibrate it all, it was spot on.  

I didn't need ANY offset at all.  

NOW THAT IS A FIRST FOR ME!

So now I'm just testing things to see if there will be any drift noticed.  So far I haven't seen any at all.  

UPDATE Jan 24, 2016:

It's now 10 days later since I set this up.  Frequency hasn't drifted in any noticeable way at all.  I'd call this success.

NASA DWPR 2015-07-30 Interference @ 50 MHz

NASA Form to report reception of this sort of interference

These two video's show the NASA KSC DWPR very strong into the 50 MHz Amateur Radio Spectrum allocation.  These video's show 2.5 MHz of spectrum starting about 49.000 MHz. 

To view more like this back as far as 2011 visit this YOUTUBE Playlist

The following is what the DWPR might look like if you only have a limited spectrum display.
Note the ON/OFF nature of it.  Also the Spacing between carriers changes as the pattern changes.  Sometimes they'll be closer (more of them) sometimes less.

Click to Zoom

This Radar's location is at about EL99pp Maidenhead Grid Square.

• Work Begins to upgrade drwp @ NASA
• KSC writeup on DRWP
• Some detail about the system
• More in-depth Detail
• ITU M.2013 mentioning WPR @ 50 MHz
• 50 Mhz Doppler Radar Wind Profiler Filters

Airspy ADC1 HF - without HF upconverter

About a month ago I bought a used Airspy and have been using it with good results since then.  Anyone who's been following this blog knows I've been in search of the most frequency stable SDR setup I could build or cobble together for several years.  I think I've finally come up with a combination that meets my requirements.

I am an avid CW operator on the Ham bands.  So any drift from an RTL, Funcube, HackRF, Airspy setup makes it a hassle to continually re-calibrate HDSDR for the drift-of-the-moment.  Some setups (even the Nooelec TCXO RTL) drift way to much to be useful and practical for CW operation.

My setup is like this.  My Primary Transceiver is a Yaesu FTDX-5000.  It comes with a 9 MHz IF output on the back of the radio.  This is then connected to whatever I'm using as the SDR to feed HDSDR software with IQ data in order to visualize the band I'm on.

Since 9 MHz is lower than most of the Cheap SDR's can tune to (most seem to stop around 24 MHz for the low end) I've needed to use an HF Upconverter.  The commonly available upconverters have drift of their own which further exacerbates the overall displayed drift.  Total drift on some setups has been as much as 1khz!  So when I'm using narrow filters, and trying to click-tune to a signal I see I end up way off the actual signal, and have to fiddle around to try to get zero-beat on it.  

I spend most of my time on 50 MHz, so this 'fiddle-time' can mean the difference between coping a callsign, and never hearing it again.

After reading reviews and doing a little research on the Airspy SDR I decided to buy one.  Two major factors for me that seemed encouraging are that the Airpsy is a 12 bit SDR instead of only 8 bit.  This a huge difference.  The other was that the Airspy has the ability to be 'clocked' by an external 10 MHz source.  It so happens that I have a Jackson Labs "Fury" GPSDO which uses GPS to generate an accurate 10 Mhz Sinewave as a clock output.  This is then connected via an SMA<>MCX connector and plugged into the Airspy.  The Airspy detects that the signal exists and syncs it's internal clocking to it which causes it to never really deviate (drift) in frequency.  I have yet to see it drift using this setup.  

The trouble that still existed was that I still needed to use an upconverter to get my 9MHz IF into a range that the Airspy would receive.

I recently read that it was possible to connect an HF antenna to the "ADC1" port internally on the Airspy.  I read that there was also some special Firmware developed to enable use of the ADC1 as the Airspy's input.  So I bought a cable with the proper connector to fit the port on the Airspy, I connect that to an band pass filter, and the filter connects to an LNA which then connects to the 9 MHz IF out from the FTDX-5000.  I flashed the firmware on the Airspy with the special firmware to enable use of the ADC1, and talked IW0HDV into creating a special EXTIO DLL that would UNLOCK the low end (HF<24 MHz).  He sent me an experimental version this past weekend and today I set this all up as I just mentioned.

And wah-lah!  It all works.

Note the small coax and connector at the bottom of this picture.  This is the connector and coax that runs from the ADC1.  The MCX/SMA on the right side is the GPSDO input connector.  The white cable is the USB for the Airspy.  NOTE: that the normal SMA connector is not used.

Bottom of the image shows the Mini-circuits BPF (band pass filter) above that is the LNA HF http://lna4hf.blogspot.com/ top of the image runs directly to the 9 MHz IF from the FTDX-5000.

Stay tuned for some more images, and possibly some video of HDSDR running with this configuration.

Update

After a few weeks of testing a few very strong openings on 50 Mhz (40/s9 type openings) I realized that I needed to be able to control the signal strength input to the Airspy.  I tried to simply add a 30 db step attenuator inline, but as soon as I added as little as 1db all signals would drop out on HDSDR.  

I contacted W9RAN who was the first I'd seen attempting to use the DDC method to operate the Airspy on HF.  After some discussion I decided what I need to try to do was to increase the gain, and see if I could use the step attenutor without signals completely dropping out.

I added a 34dB+ gain Miteq LNA which covers 1-100 MHz.  And a static 10dB minicircuits attenuator.  This sould give me about 24db gain to play with.  And I can then attenutate signals to -6dB below what is coming out of the FTDX-5000.  The point being I need to be able to see weak EME type signals but be able to attenuate way down when need be.

This seems to work.  I can operate the 30 dB step attenuator all the way through Max from 0 without having HDSDR completely drop out.

I have a second 30 step attenuator I may attempt to add to the chain for those extremely strong 50 MHz openings.

On HF I have a lot of local line noise garbage, but this'll give you an idea how it works at least.  I mostly work 50 MHz here.  Also I don't use the Audio output form HDSDR except to feed IQ to CW Skimmer.  So I don't normally use the audio out to 'listen' to.  It just gets piped to VAC and on to CW Skimmer.

I'm also seeing some images in this that are probably coming from up-band, so I'll be working on a better pass band filter for this.

Also this demo doesn't really show you what I was most concerned with unfortunately; that being freq drift of the TCXO RTL vs. Airspy.  But I'll just note here that the drift is ZERO.  Nothing I can detect anyway.  It works perfectly for my needs.