For a long time now I have been thinking about buying an SDR radio.

I have plenty of low cost RTL dongles, they represent great value for money and are good for experimenting with the concept of SDR but when it comes to listening to steaming digital audio over several frequencies rapidly on lets say the AM airband, the cheaper $20USD DVB-T dongle types have their limitations.

I tried RTLSDR-Airband, a program for raspberry pi.

https://github.com/szpajder/RTLSDR-Airband

It seemed to offer all I was looking for and I gave a fair go with a raspberry Pi-2 and RTL-SDR dongle V3 ( an excellent device for a beginner by the way), but unfortunately I couldnt get to grips with this program. It is largely a linux based program which is fine and I had it running all okay on the raspberry pi scanning away 2 banks of stored frequencies as a trial ..BUT, trying to monitor the audio using a windows machine is where I came across problems. I suspect it would be a whole lot easier if I had used a linux distribution on the laptop/ monitoring device.

Monitoring will work on windows I am told. The author was very helpful but alas I have to admit I gave up after a few weeks of jumping through hoops trying to get it to work.

Nice program idea though, I have no doubt that over time things will improve/develop with this project.

So I looked around the internet and consulted plenty of forums.I wanted an SDR radio that I could use with a raspberry pi3 or similar single board computer attached to my home network acting as a radio server.. and log in to this server from a laptop or windows tablet in another part of my house to monitor the audio.

There are some very good radios out in the marketplace at the moment for the hobby listener, some with huge followings and excellent reviews.

Airspy,SDRPlay,Funcube etc can all be attached directly to a computer and they work fine for their users..But

One SDR radio stood out from the rest or my needs, the Airspy R2, a device created by Youssef Touil from France who is also the creator of SDR# (SDR Sharp), perhaps the most popular radio monitoring program in use today. .

What set this apart from the rest was the program used to stream the audio over a network.

The program called spyserver is available for linux / raspberry pi and it is quite easy to install.

I think where this program is different from all the other offerings is,

  1. The bandwidth traffic rate used across a network is relatively small so if care is taken a raspberry pi 3 can be used with no audio drop outs.This is a huge plus if you want to access the device remotely from another part of the house or even the garden like I do.
  2. Ease of install/use plus due to the massive following/popularity of SDR sharp, the comfort in knowing that any bugs will be addressed very quickly.Also, new plugins are constantly being developed by the SDR sharp community.

One thing I should mention before going any further is anyone who is thinking of setting up a raspberry pi with spyserver, and monitor on another device using SDR sharp you should consult two excellent website guides. Both are very good indeed and will help you a lot.

Firstly Mike Richards G4WNC a fellow radio amateur from right here in the UK , his excellent webpage guide is below.

https://photobyte.org/running-spyserver-raspberry-pi-3/

Next, another excellent guide, very detailed and superbly written by Whitham D Reeve, a very accomplished Engineer from Alaska USA.

http://www.reeve.com/Documents/Articles%20Papers/Reeve_RPi_AirSpyServer.pdf

Special Thanks to both authors, these are great resources for the newcomer to SDR radio.

Also I should mention the quick start guide by Airspy which covers most things.

https://airspy.com/quickstart/

 

Anyway, an advert appeared on a national used goods site for an airspy combo (airspy r2 and spyverter HF converter) so I contacted the seller Iain (another radio amateur btw), he explained he bought it new a few months previously but never really used it a lot and he was having a “radio clear out”.The deal was done on the phone, the unit duly arrived next day in the post.

Both parties were more than happy. Great Price, lightning fast delivery ! Thanks so much Iain !

Note that the unit came with a generic micro usb lead, more on that later.

For the purposes of this blog post I will concentrate on the Airspy R2 SDR radio, I will leave the spyverter HF converter for another post on another day.

The Airspy R2 is a lots smaller than I expected ,around 53mm x 40mm x 25mm.

It is encased in a heavy duty cast aluminium box which has been powder coated.The unit feels very solid and and extremely well made. First impressions on the product are very good indeed.

Lets have a look inside.

Airspy R2 PCB layout.

Amazing what manufacturers and designers can pack on to a small pcb using surface mount technology, there is a hell of a  lot going on in here !  Note the si5351 clock chip…an interesting addition in itself. I think its the 5351c which has 6 or 8 clock outputs in one little IC package. As I said, a lot going on.

Now the underside, I dont know if you spotted them but it looks like there are 1 or 2 leds here to the far left, why are they here when a user cannot see them when the case is back on ? Presumably placed there for testing/diagnosis.

I guess there was a choice, laser cut another hole or 2 in the aluminium case for flashy leds which pleases the user or hide them inside and have greater protection from unwanted signals entering the case..the latter won.

Airspy R2 underside PCB detail.

One thing which has been improved on the R2 is the micro usb socket, this has been strengthened compared to the earlier Airspy R0 model. One other difference between R0 and R2 is the gold edging around the pcb which is said to enhance performance.


 

Setting up airspy/raspberry pi3 and spyserver.

Now on to the radio server, a raspberry pi 3, they are cheap,reliable and easy sourced.

A pi3 is not the best choice for this task , it is nothing like an Odroid XU4 for example which would be best but it meets the minimum requirements, and here we are experimenting, so a pi3 it is.

One thing you have to remember when migrating to SDR radio is that these marvelous little things work in a totally different way to an old school analogue radio. All the audio you hear from the speaker is digitally processed, that includes the hiss and all the interference so there is a lot going on inside todays sdr radios and we will be asking a lot of the £30 GBP raspberry pi3 with 1gb ram and limited cpu/usb speed to process all the audio on the fly.

First thing I did was to fit a heat sink kit, the pi3 will be working quite hard resolving all those radio signals, anything to mitigate heat build up on the cpu and ram has to be a good move. The heat sinks are in a 3 piece kit, self adhesive, they are very cheap to buy and really easy to fit.

Here are a pair of pi3 boards, one with heat sink and one without to illustrate locations.

Raspberry Pi3 heat sink locations for main CPU (gold) and LAN controller (blue).

 

Raspberry Pi3 Heat Sink location for RAM chip on the underside.

 

Box it all up and use a reputable 5 volt dc  2.5 amp power supply, I used a screw less case and psu from the raspberry pi foundation. Too many problems can be caused later on by unreliable power units. Make sure to get one that is stable and up to the job.

When wiring up, locate the pi3 close to router or a wired LAN point in your home and connect the LAN using an ethernet patch lead, this will give best results.

I turned off the pi3 internal wifi and set a static ip address for the pi3. Also I enabled SSH connection which is done via the menu accessible by the command

sudo raspi-config 

When you power up the pi,you can return to your monitoring position/device and use PuTTy program to communicate and send commands to the pi3.

 

Now, about the USB lead that connects the pi3 and airspy R2. This item has caused so many issues for other users. There are lots of stories of noise appearing in the audio and in the waterfall of sdr sharp when using generic inferior micro usb cables. Some users have installed ferrite rings or snap on ferrite tubes to combat the noise. The factory supplied cables are much better quality apparently but these are unavailable from ITlead as a spare as far as I know. Some micro usb cables have appeared on auction sites with ferrites bonded into their construction. They sell at a premium price though.

 

My unit came with a generic phone type micro usb lead about 6ft/1.8m long, sadly not the original one and when I tried the Airspy coupled up direct to my laptop, I had the same issue of noise.

I tried to find the source of the noise, perhaps it was an appliance in my home but no luck.

I was considering at one point to make my own cable using belden 2 pair individually screened and twisted pairs, that maybe a job for the future.

I decided to do a little research and the name Blitzwolf came up as being recommended by another airspy user on the official user group. He had used the red blitzwolf “ampcore” 3 amp rated cables which were around 6ft/2m long and priced at around £5.50 each.

The more I read into the specs, aside from the length there seemed very little in the way of difference apart from price between these and the Blitzwolf plain black version BW-CB7,

In theory the shorter the cable the better as there is less chance of unwanted signals entering the Airspy via the back door.

…So I went for the 1m black version BW-CB7 priced at just  £1.62 or $2.10 usd each or if you buy more, discounts are available at the moment.

I purchased 4 pcs for just a shade over £5 GBP delivered.

Here is the link to the product, Banggood product ID: 1027785.

https://www.banggood.com/BlitzWolf-BW-CB7-2_4A-3ft-or-0_9m-Micro-USB-Charging-Data-Cable-With-Magic-Tape-Strap-p-1027785.html

This Blitzwolf BW-CB7 cable is rated at 2.4 amps with 21AWG power wire and a 30AWG data wire pair, its overall screened (not individual screened data pair which would have been brilliant btw) ,no ferrites on this.

I purchased a couple of their cables from a supplier in China called Banggood.

They arrived in a few weeks and they seem very good quality indeed for the cash. Nice cable !

Here are some photos. I will make no excuse for being over enthusiastic with the photos as this is a small but very important part of the set up of SDR radio.

Blitzwolf BW-CB7 Cable.

 

Connector Close up Detail.

Roughly 3.6mm overall cable diameter which is good for micro usb.

Connector end detail

 

A secure good fit into the Airspy R2 micro usb header.

As soon as I installed this cable, there was a vast improvement in reception. The noise was a fraction of what it was when using the purple braided generic 6 footer that arrived with my second hand airspy.

Blitzwolf sell cables on Amazon also but they do not stock the BW-CB7.

Only their Chinese distributor Banggood have those I think. A bit of a bargain for the price paid.

On to running spyserver on the pi3 and here is where I had a problem issue which persisted and went on and on for days.

Looking back its quite easy to spot my mistake (totally my error) but here is the essential stage in the process of getting clear unbroken audio when running the pi3 as a radio server with spyserver.

Dare I say it, perhaps a bit of a mistake by those who wrote the spyserver program.

If you have followed the instructions on either of the two website guides in the first part of this post you will have downloaded rasperian lite and spyserver and be all set to go. You will be familiar with the spyserver.config file.

By default the spyserver.config file text looks something like this, note the line about half way down this file which deals with custom sample rate, use the down arrow key on your keyboard to navigate the cursor and find it.

Standard/Default spyserver.config file value for sample rate.

If left as default (as above), the pi3 will struggle handling the data over its usb port.

This is because the custom sample rate line is commented out with a hashtag and if left this way spyserver will “fall back” to its “safe” defaults and ..strangely in my opinion.Spyserver will automatically set the highest rate possible for the device that is connected to it.

In the case of the R2 this is 10000000. The raspberry pi cannot handle 10000000 and so this will lead to no end of problems trying to resolve the audio at the monitor end. You will get jittery audio, drop outs and freezing of sdr sharp.

To cure this we need to specify a lower custom value of  25000000 setting for the R2.

(If you are using airspy mini with a pi3,the value would be 3000000, and RTL stick the low value is 32000000).

Important : If you input an incorrect value for your device type, spyserver will “fail safe” and alter the spyserver.config file to the highest value correct for the device connected to it…be warned.

Now the method for the fix.

Open the config file in nano editor, at the pi command prompt

naviagte to the loacation on the pi that has the spyserver.config file. Typically open a ssh terminal in Putty or similar and at the command prompt type the following

cd spyserver

then

sudo nano spyserver.config

Now use you arrow keys to move the cursor to the custom sample rate line and remove the hashtag with the backspace key.

Ensure the value is set to 25000000 for Airspy R2

You should end up with this

edited/correct sample rate line for raspberry pi3.

Now save the config file with Ctrl + X and Y to save changes.

Restart spyserver and you should find all is well with the world again.

With a bit of luck, You can now hear streaming audio coming from the pi3 & airspy on your laptop/tablet running sdr sharp.

 

Heres an example of the output viewed on a very modest (sub £100) Lenovo T400 dual core laptop 4gb ram running SDR# ,and spyserver running on my raspberry pi 3 in another room. “Air Italy 90 mike” , “Qatar 8102” cargo and a few more are checking in with the controller.

The audio was streamed via my home network wifi.

 

In the video below, Note the very low network bandwidth to transport the audio of between 32 and 34kb/sec !

 

Hint :Hit the full screen icon bottom right of this mp4 video for ease of viewing as its too small to view any detail within this page.

 

 

No drop outs, no jitters or freezing.

I hope this setup tip helps you.

 


 

 

What I like so far about the airspy R2,

1.The ability to stream airband audio effortlessly over my home network to any device running sdr sharp. Amazing

2.Unit pcb quality, excellent !

3. Software/ Custom Plugin/addons availability and constant development.

4. Due to the Huge cult following of SDR Sharp there is always help on hand out there on the internet..If you have an issue,chances are someone has been there before and found the solution.

5. The performance from this little tiny box of electronics is nothing short of astounding. You have to step back sometimes and remind yourself, this sells for circa $200 usd or so new,yes 200 dollars which is absolutely stunning  value.

I have owned many radios over 30 years or so of listening to airband etc, good ones and bad ones. Dozens of them, many costing substantially more than $200  But price aside, the performance of this makes it one of the best radios I have ever owned. That has to be some kind of accolade..it is to me anyway.

Yes it isnt perfect, yet… but this is only the start of the SDR journey for me. I have every confidence that I will achieve my ideal set up with my little airspy. If you like tweaking settings and controls, you will love this.

Radio has moved on…massively.


What I didnt like,

  1. The way spyserver defaults to highest sample rate. Surely it would be wiser to default to the lowest sample rate of the device connected to it. This way a new user connecting his/her new device will, at the very least, get satisfactory results very quickly. Then a user can change/edit the spyserver.config file should they require increased performance or enhancement later on.My view/opinion only but I have put that suggestion out there via this post.That hashtag is easy missed in the config file. It caught me out.

What Im unsure about or cannot do so far, Help required please.

  1. Make a few banks of memory channels and scan them accurately and fast just like an analogue scanner.

I did try the Frequency Manager Suite for sdr sharp by Jeff from the USA.

http://www.freqmgrsuite.com/

This worked quite well  and the frequency manager options were particularly good …BUT The best I could do was a scan rate of 2 channels per second with a pi3 running fm suite. Scanning was not perfect and often the scanner would skip an active frequency. I tried reading the user manual several times and changed settings to fastest scan, signal threshold was set right but still I had issues and I gave up.Perhaps its my setup, the limits of a small computer like the pi3, or my settings which I changed lots. Well done Jeff, Excellent work, nearly there but not quite.

 

UPDATE ON FREQMGSUITE for SDR# (Feb 2019)

Following much tinkering, I did get the scanner in freqmgrsuite working reliably.

I created a group called Airband and inserted about 6 civil airband  memory frequencies into this group.

I adjusted many of the settings over a an hour or so and found that if I kept to less than 10 frequencies in a group (or bank as we used to say) then the scanner works. Its not going to be blisteringly fast but it does about 3 ch per sec which is enough for everyday listening.

I certainly recommend a good read and digest of the manual for freqmgrsuite..several times over.

This is really excellent stuff, Well Done Jeff and thanks for your contribution to SDR radio.

Heres a screenshot of the scanner working some airband memory channels, you can see these in the right hand column.

Click on the image below to expand to full screen.

 

 

 

 

2. I heard of a good scanner for sdr sharp developed by SDR user Vasily from Russia I think.

http://www.rtl-sdr.ru/page/obnovlen-skaner-4

You will require google translate as the page is in Russian language.

Unfortunately the lastest issue of his program doesnt have a memory channel scanner, but it does scan between 2 set frequencies and it does this blisteringly fast. I can scan the whole military airband 230-390mhz in 15 seconds using my pi3.

Please Vasily can you put back the memory scanner ?

Does someone out there know what plugin i need ?

 

3. When I remote ssh into the pi from my monitoring device I notice the following,

If I run spyserver (./spyserver) from a ssh terminal the program starts fine but I cannot exit back to the command line in that terminal window, I have tried esc key, the q key, typing quit, typing exit  all of which dont work. Readers..Help Please, is this possible ? Thinking about it , perhaps not as this would cause spyserver to release the device.

Just a niggle, I have to open another session to get to command line. No big deal.

Also, on some occasions the aispy fails to wake up, I have an idea to fix this by setting up a cron job and pinging my router every minute 24/7/365.

Would this work or is the issue likely to be the time value set in spyserver.config ?

Readers, If you can help me with my requirement for a scanner plugin that will scan stored memory channels quickly or any of the above points, please use the reply form. Thanks.


 

To conclude,

I like the Airspy R2, its a brilliant device for a hobby listener. So many things you can try out with SDR sharp I will be quite a while experimenting.Still cant quite believe what a customer gets for just $199 new.I recall only a few years ago Digital Signal Processing in a receiver was only for the rich.

There are a plethora of audio and IF filtering options in this little box of magic when teamed up with SDR#.

This is serious radio kit ,and well worth the cash.

 

 

The scanning future is here,it is without a doubt, SDR radio.

All of the big manufacturers of amateur kit have made the change, and what a sea change it is .. there is no turning back.

 

 

 

Finally,

There are some really neat devices out there in “radio land” at the moment.

I couldnt write this without mentioning SDRPlay.

Developed and made right here in England UK which is fantastic.

The RSP1A model in particular is brilliant value for money.

SDRPlay have sold many thousands of units worldwide. They have a huge following of happy users.

I particularly like the look of their sdr uno software, very nice indeed.

Just this month Feb 2019, Jon Hudson the boss from SDRPlay announced a scanning facility for sdr uno.

I must try one soon to compare to my airspy.

I would be very interested to see if the network streaming facility is as good as the one from airspy.

 

It is great to see radio developing so quickly and top quality devices you could only have dreamed of a few years ago are now available at relatively low cost to the hobby listener.

 

 

 

 

 

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