Wednesday, September 21, 2016

Big back yard loop antenna gives low noise and excellent transmission

In Amateur Radio experimenting with antennas provides some of the most interesting results for the least amount of money, particularly if you mess around with wire antennas. Improvements to the antenna provide much greater benefits than money spent on transmitters or amplifiers.

In recent months I've been using a doublet hung from a gum tree fed with open wire feed line. To make it work on 80m I extended the ends in a "dog legs" back along the side fence lines. This arrangement works on 80m, 40m and 20m. While there are good reports of my transmission, reception has been very noisy, particularly on 80m.

This week I turned it in to a big loop by closing the ends and hanging them from the house.




It tunes up easily on 80m and 20m and with a little difficulty on 40m. Yesterday I did a lot of tuning around and listening and experienced very low noise with big signals. Today, I had a test QSO with Patrick, VK2PN who reported excellent signals from me, especially on 40m.

More detail: The loop is simple figure eight lamp flex (half) roughly joined with knots and screw terminals - this can be improved. 450 ohm slotted feeder runs down to the shed and is terminated with a 4:1 balun before the rig's auto-tuner.

Monday, September 12, 2016

Generate morse code followed by spoken letter audio files

I've had several shots at learning morse code. In episode 108 of the excellent QSO Today podcast, there was a great suggestion that the guest learned morse code by listening over and over to a recording of morse code characters followed by the spoken letter.

Despite hunting the internet I could only find other people looking for similar drill tapes but no actual audio files.

macOS has an excellent text to speech synthesiser so I found some software to convert text to morse in a wav file and combined it with the macOS "say" command and now have a system that can generate random sequences.

You can hear a short sample here.

I've forked the original repo and put my version here. The bulk of the work is by Thomas Horsten but hasn't been touched for years.

I've done the following:

  • Made it build on macOS, note it needs libsndfile (brew install libsndfile)
  • generate.py generates wav files for the morse and spoken character
  • makePractice.py makes a wav file with random sequences of letters

The silence between the morse character and the spoken character can be tuned as can the silence between groups.

I've put a full length drill recording up here. This one repeats each letter three times.

Sunday, September 11, 2016

Malcolm Sinclair, VK2BMS, has died.

Sad news. Mal was found this morning at home. He was active even yesterday on 20m talking with old friends but clearly very frail.

Mal was a regular on 20m talking with ZL and he had a big signal on 80m where we talked every Sunday.

A kind man, very concerned for the welfare of animals and nature. His cat Rosco is being looked after. We will miss him very much.

VK2BMS  SK.


I recorded a chat with Mal in May 2014, here are some notes.

“In town you see a hobo lying on a park bench a few years ago he was a little boy playing in a school yard”

Mum had an Irish grandfather and a British grandmother and they came to Australia first but didn’t like it. They moved to a place on the South Island called Little River, Akaroa, tour ships pop in there now. Then they moved to a place called Southbridge about thirty miles out of Christchurch. 

My grandfather was marvellous, he was a shoe maker, he would just reach down and put his hand on a person’s foot and go away and make a shoe. He had a horse and cart and when he’d go up the driveway with a gravel path and it would make a noise and the Maoris would turn the lights off and pull down the blinds like there was no one home - he used to laugh. He had a shop “Tom Taylor”.

Dad was involved in installing and servicing theatre projectors. At one stage work was done to install a 35mm projector outside at home, holes were cut in the wall, a big concrete block house it was, there was a tin lined projection box, but in the end it never eventuated. He was always away somewhere, sometime he took me with him, but I never got to know him very well. He died at about 54, but he lived a life. He worked hard and played very hard. He’d think nothing of working, installing projectors, twenty hours a day. Everything had to be perfect, he had all these test records, one was “The donkey serenade” he knew all the notes to that and how it sounded on the speakers. 

He was installing some gear in Napier, up in the operating box, and an earthquake came along (in 1932). Everyone panicked and he said “stay here” but they rushed down below and the whole thing collapsed. Fortunately he was in the small tin lined fire proof box. When it crashed to the ground he stepped out, the only person to survive.

My parents were married on Remembrance Day, which in those days was taken very seriously, the whole town stopped and dad thought all the traffic was stopping for him. In those days it was pretty “big time” having a car, dad always had a spare steering wheel and when all these cars stopped very suddenly at 11am dad drove straight through waving the steering wheel. If anyone did anything stupid on the road he’d wave the steering wheel at them and they’d just about faint.

I was born on the 17th December, 1932 in Wellington, New Zealand. No brothers or sisters.

School was first at a private school called Inahow, there was a Miss Dunning, a very prude lady who used to get all the children together in the kitchen washing up area and wash my mouth out with soap for swearing, I probably said “damn” or something like that. 

Then I went to Ridgeway Primary School but that’s where things were difficult, I could never catch up with the mathematics. Mum and Dad meant well, sending me to the private school, but I could never catch up. From there I went to the Wellington Technical college, and studied general engineering.

We used to go on school holidays down to a place called Radio Corporation of New Zealand there was a guy there named Marks (might have been Marx), he was a good cobber, you never paid for anything, it was always “mates rates”, he’d fix amplifiers and get things. 

First job was with civil aviation. I wanted to become a radio engineer but the mathematics “unzipped” me. I lasted there for a while but decided it wasn’t for me and I became a bit footloose in various jobs, but then for some reason I got a second job, working for an alarm firm, initially outside,  then they brought me inside looking after the general office there. I used to open the place up in the mornings and one day the phone rang and I said good morning and the woman said “oh it’s very early, are you a recording” and I said “yes” and she said “I’ll phone back”. 

I got my Ham Radio license about 50 years ago. I had sat the license before that, it was in the days of Morse code, but I didn’t feel I was up to the morse test, which was in the morning so skipped it and when I walked in to the second exam this bombastic person yells and screams at me in front of everybody, which I’ve never liked. If you’re going to yell at someone you should do it in private. Eventually he ran out of steam and so I replied in kind. I passed the paper but hadn’t got the morse and so wasn’t licensed.

I was friends with Noel Mullis, ZL2APZ who eventually became a radio inspector, he said you’ve got a ZC1 - an ex New Zealand army transmitter receiver in a metal box, he asked if I could get it going as he wanted someone to check his signals. So I dragged it out, I could see where the mice had been so I cleaned it out and it leapt in to action and I could receive. So that re-kindled my interest. That was about six weeks before the exam so I immediately applied for the exam so I had to get cracking on the morse. In those days they had volunteers at the VK2BWI (in Sydney) who ran morse practice every weeknight which was great.  Oh, the static crashes were horrendous but after a while you got used to that. 

So I went and sat the morse exam and blokes were swearing and throwing their pens down but to me that was just a bit of static. They were putting other people off as well you see, so there was only a professional operator and me that got through the exam. I was pretty pleased about that.

I was licensed as ZL2BAA which was the first of the B calls, (Noel might have had a hand in that). So I got on with the ZC1 running five watts of AM. Then I got on to higher power CW and that increased the range of course.



In the job at the alarm firm, I saved up and had enough to either go to the U.S. or see all of Asia, I thought well Asia’s pretty different so chose that. I’d annoy the boss by sending telegrams and he’d put a pin on the map, and when he saw the “U-turn” he knew I was coming back.



I met Caroline in the South China Sea. She did the manuscripts at the Australian Museum. I’ve always been a museum fan, so we struck up a conversation and became, well um, do you want to come to New Zealand or do you want to come to Australia? At that time Britain was about to join the European Economic community and New Zealand’s trade would be hit. So I came to Australia and stayed with her parents for a while but then got a pokey little boarding house room in Sydney. 

Caroline lived at Epping and I’d catch the train and walk out out there every Sunday. We used to watch The Two Ronnies on television. Eventually we bought a house in Willoughby East.

Looking around for a job I saw an ad in the Sydney Morning Herald for a sales position at Ferguson Transformers. I’d never been in sales before but they recognised that I could pick up knowledge of the products and they’d help me with sales. I worked there for about twenty years. After a couple of changes of management, I “decamped” thinking it would be easy to find another job aged in my 40s. 

Eventually I got a job at AMP as a “desk jockey”. There’s a difference between technical people and non-technical people. My humour was sometimes not appreciated but I stuck it out and retired at age 67.

Caroline worked for the Australian Museum, in touch with the scientists all the time, and she spoke to them and asked if we have children, when they grow up what’s the population situation going to be? Well Caroline, we predict that (by about now) the population of the world will be about ten billion - oh no! So, we didn’t have any children. We were worried about the outcome. In my opinion, a lot of human beings are not very nice people. So, ten billion of them, to bring a child in to that, ah no, not guilty. 

It may be that being a single child and not playing games and such I was more interested in nature, the ants in the ground, the birds, I developed quite an affinity with them and I’ve been interested in animal welfare ever since.  

After a talk by ethicist Peter Singer, I told him he was starting to put him off eating meat. Singer said “oh good” and signed a book for me with “Malcolm, eat well”.

I’ve only been a vegetarian for four or five years, although I’ve been thinking about it for years, but one night, I got the piece of meat on the fork and put it in the mouth and said “right, that’s it, bang”. I feel a bit better for doing that. 

I’ve always had a left wing leaning. It probably gets back to the “fair go” style with animals. I think you’ll find, from my experience, it may just be the people I mix with, that most animal activists, if that’s what you want to call them, are of left wing tendency. It’s compassion and fairness for all. 

A couple of Saturdays ago we had a “park day” and a bloke phoned me in the morning and said that he’d like his boy to come along as part of the Duke of Edinburgh award. So that was OK, but he brought a long of big packet of McDonalds biscuits as mum worked at McDonalds. At five o’clock, mum arrives in a brand new big Audi sports car and I thought, gee she must be short changing some people at the counter. But no, she was an executive.

Morrie used to live just down the street from me (in New Zealand). We used to live in a suburb called Brooklyn  about 400 feet up, a pretty good location, overlooking the harbour. Matter of fact on my QSL card, ZL2BAA, I’ve got a photograph of the Southern Cross (ship) off Wellington with Brooklyn in the background.



There’s a bit of a story about The Southern Cross too… I was talking to a bloke who was on the Southern Cross, a beautiful ship, and I was on holidays, aged about 21, something about radio came up and he said “I’m the radio officer” and he offered to show me the radio gear, so we got on board, very palatial surroundings, and he said “I’m not really the radio officer” but I just wanted to have a yarn with you. I spend plenty of time at sea and get pretty lonely.  

Next thing, the ship’s vibrating and I said what’s going on here? I’d better get on deck for some fresh air but there’s no wharf there. What to do? If I present myself to the captain I’d be a stow away. He said let’s go down to the mess and have a meal and a drink. There was a vacant cabin next to his. He seemed genuinely lonely but he seemed harmless but perhaps I was a bit naive. So I’m in this cabin and next minute over the speakers comes “close all watertight doors”, they had to go upstairs for lifeboat drills and I’m down all by myself. All I could hear is the sea swishing past. Then clunk, clunk, clunk, “open all watertight doors and a ships inspection”. So I got under the bed. I felt like some poor animal being hunted. 

The next minute bang! the door opens and there’s two highly polished shoes about two inches away from my nose.  I’m there almost not breathing, anyway they go away. I get out from under the bed and we finished up in Auckland fortunately. I had to get a bus back. Beautiful smooth trip.

I knew Peter Hughes, N3PH who worked as Radio Officer on the QEII. He was married to a New Zealand girl Alison, he worked in Wellington for some time which is how I knew him but he got a job with the Cunard line and I’d visit him whenever they were in town. People would say they’d love to go on the QEII and I would say that I’ve been on the QEII many times! 

Caroline died about eight years ago, I don’t remember the date, I only remember two dates, my birthday and my mother’s birthday - she was the 21st of June, she’d say “the shortest day and for you young blokes, the longest night”. 

My mother was a bit religious, mainly for social reasons. I used to go to Sunday school but they’d start putting all sorts of rhubarb across about a boy trying to steal a lolly out of a jar on the counter and the alarm going off and I thought “this is ridiculous” and went home but mum said “go back, go back” - worried about the social aspect of it you see. But dad said, whatever he wants to do he should do. So that’s where it first started. 

When you die, “I think you’re gone”. A lot of people want to believe. It’s something to cling to. These religions, they work on fear, sin and guilt. If you go and do so-and-so, you’ll go to hell. These people are genuinely terrified. Anyway, when they come to the door I always ask them about the father of Jesus. There’s a book called “The bible fraud”. 

My influences? Well, I don’t know that anyone influenced me. A barrister friend of mine once said, you know Malcolm, ninety percent of people don’t think. They watch all the glamour people on Channel 9, listen to Alan Jones, see the football and that’s it. It’s a great diversion is football, the politicians love that, it gets them off the minor things. He said, without that ten or even five percent we’d be jiggered. When a dictator takes over the first thing he gets to is the intellectuals. They get rid of them. 

After Caroline died, I used to go to Jazz at a pub called the “Vanity Fair”. It’s funny how when you go to a place regularly you tend to go to the same place and I’d stand near the band. I’d see this lady over the other side and she was quite an intelligent lady. I get the brilliant idea, quite romantic, of getting her a schooner of Kahlua and milk. So I’m just about to approach her, someone inadvertently turns and nudged me and I spill it all down her cleavage - how romantic. That’s how we met. 

I like traditional Jazz. In younger days I would go to Jazz three or four times a week. Now and then Dave comes down and we go and see something.




At home with Robert VK2ZNZ


At home during the interview written up above.


Inspecting some radio gear with Robert VK2ZNZ


At the bowling club with Dave Russell VK2DKE


Happy days soon after moving to Sydney. (From Noel)


Friday, September 09, 2016

EZ-Radio Databox interface for Yaesu FT-817 etc review

There's a new radio interface box on eBay out of China that looks interesting. It's about half the volume of a SignaLink USB and at AU$84, significantly cheaper (compared to about AU$160).

The extruded aluminium case is sturdy but has PCB front and back panels. The holes for the RJ45 and USB socket were not well aligned for me and I had to take off a panel and nibble them out a bit to be able to insert the USB plug.





Internal construction is very good.


It comes with a full set of cables but no documentation. The web address http://ez-radio.com simply diverts to sales page which can be translated by Google as follows:

"This product is YAESU radio station connected to the computer, make use of digital communications, and other functions.

Use this connector, you can use the radio to do PSK, RTTY, SSTV, CW and other digital communications.

Products using the US company's Silicon Labs CP2102 USB2.0 interface chip, strong and stable performance, the replacement of the USB interface, the port number does not change, reducing the chance of error in the connection process.

Computer terminals and radio terminals Ground Ground product is completely isolated, and the housing and the end product is connected to a computer, and the computer to prevent Ground stations have pressure, there was a slight sense of shock by touching.

This adapter box can use to automatically reconcile CAT-day connected to the computer! Some HAM need to use automatic day reconcile CAT interface so that you can adjust the day connected to the fuselage behind the CAT interface connected to the computer interface from the microphone in hand drawn, original machine hand microphone connected to the adapter box, so you can hand microphone, computer, day tune while using independently of each other!
Because YAESU FT-857/897 and other models DATA interface only supports audio input DIG mode, the FM or other audio input mode can not be, this may not be supported in some applications, for example, do SSTV communication in UHF FM mode this product based on this defect, made ​​some changes, the audio signal can be through the microphone interface or interfaces into DATA, so that regardless of the kind of pattern that you can use this frequency for radio input audio cassette adapter! True all mode, full-featured!

Support Radio models are:
YAESU: FT-817 \ 857 \ 897 \ 7800 \ 8800 \ 8900 \ 100D \ 450, etc.
Packing List:
1. a transfer box
2. Akihabara 3.5MM audio line two
3. a high-quality USB cable
4.CAT line
5.DATA line
Driver and related software download link :( need to copy into your browser address bar to open)
Driver (must be installed):    http://pan.baidu.com/s/1dD8JWbR
HamRadioDelux:   http://pan.baidu.com/s/1hqkrvBA
MMSSTV:    http://pan.baidu.com/s/1o6l1feU
Tutorials will be posted on the shop website www.Ez-Radio.com, if necessary, you can click to see

Product net weight: 163g, incidental wire weight: 275g, 438g total"

Observations

This device does not include a USB sound card. I had assumed it did and was a little disappointed. It is not as functional as the SignaLink USB, which I guess is to be expected at half the price.

I plugged it in with the supplied cables to the data and cat ports on an FT-817 and into an Ubuntu Linux laptop and FL-Digi was able to talk to it without any problems. The serial port came up as /dev/USB0.

The front panel has little lights that show serial communication and PTT which is handy.

As I mentioned after poking around I realised that there's no USB sound device in there so the supplied 3.5mm cables were used to connect to the laptop's mic and headphone jack. I was quickly on air with CAT PTT and all seems well.

It's not clear what the RJ45 sockets are. Looking inside (see the picture above) it looks like one is a breakout, SignaLink style, for making up rig cables. Perhaps the other one is a microphone cable - they mention the microphone in the translated text above.

Conclusion

For the money it's a decent little interface box and is fine with a laptop that has mic and headphone sockets. The mis-alignment and size of the panel holes for the sockets was a pity but easily fixed.

I could not find any useful documentation so I hope this helps anyone else who purchased one. Please let me know if you figure out the RJ45 pinouts.

Selling Yaesu FT-101 and FT-7 transcievers

A wonderful feature of ham radio field days is the circulation of second hand radios. This means that you can buy an old radio, play with it for a year or two, and often sell it for the same price.

As a teenager I lusted after the Yaesu FT-7 and remember reading every ad and review with great interest. I'd also seen the classic FT-101 but it was way out of my price range. As an adult I was able to finally purchase both of these and have my (delayed) gratification.

The shack is too full and it's time to pass them on.





They are both up on eBay for the next seven days. FT-101 and FT-7.



Both rigs have sold. 

Saturday, August 20, 2016

Low cost 2.7GHz antenna analyser

Since starting to receive ADS-B signals on 1090MHz I was wondering how well my home made antenna was tuned to that frequency.

I spotted an analyser for AU$236 that covers up to 2.7GHz on Aliexpress here and it seemed worth a try. Here it is with a simple dipole that is reasonably tuned to 1090MHz.


It's advertised as "Antenna Analyzer N1201SA SWR standing-wave meter Talent instrument Impedance tester 140M~2.7GHz" and I'm very happy with it.

The unit contains a re-chargeable battery and is simply re-charged with a USB cable. The knob at the top makes it easy to tune the lower and upper range frequencies.

Output level is -18dBm and it seems on frequency as far as my UHF transceiver is concerned.

There are two modes, one with figures displayed and the other which draws a graph as you see above.


If you need to work in the GHz range, I recommend this little analyser. It turned out my home built antenna for 1090 was a little low and resonant at 1083.3 - not too far off.

Thursday, August 04, 2016

WSPR decoding on a headless Raspberry Pi

At last Sunday's ARNSW Home Brew group meeting, Peter, VK2EMU handed me a Raspberry Pi a USB audio dongle and my mission instructions... to set up the Pi to decode and report WSPR spots in a headless configuration.

In the end I've built on the excellent work by DJ0ABR.

I had trouble recording the 118 seconds of audio at a sample rate of 12000 samples per second as it produced buffer overruns. Instead I've used the rec command from sox to record at the native sample rate of the USB audio dongle and then convert the file using sox.

I've pretty much used the code and scripts as supplied, with some modest improvements here and there.

Source code for the decoder is from here. This is a fork of the original code which has gone and been integrated into wsjt-x. I have forked it here and added my versions of the record and decode script and the simpler crontab. I've fixed a few things and pushed those changes to my fork of the code so I'd recommend that as a starting point.

Here's some spots on wsprnet.org reported from the raspberry pi:



Install a library you'll need:

sudo apt-get install libfftw3-dev

In the directory with the Makefile, type "make" to build the software.

The USB audio dongle is a low cost one called "3D Sound". I found that it picked up lots of hum until a junkbox audio transformer was wired in line.



Find the USB audio card with:
   cat /proc/asound/cards
and then create /etc/asound.conf with following:
   defaults.pcm.card 1
   defaults.ctl.card 1

# set audio levels
alsamixer # graphical in terminal

To allow the pi user access to the audio devices:

sudo nano /etc/group

and add the sound group to the pi user. You'll need to log out and back in for this to take effect.

To test the recording you can record while showing a level meter like this:

arecord -vv -fdat test.wav

Press Control-C to end the recording.

There are two scripts: record and decode. record is called from a cron job every two minutes to record 118 seconds of audio, convert it and kick off decode.

I installed in /home/pi/wsprcan

Here's my version of record:

#!/bin/bash
# WSPR Audio Recorder Script by DJ0ABR
# record WSPR signal at every even minute
# called by cronjob
BASEDIR=/home/pi/wsprcan
# number of files in wav folder
cd ${BASEDIR}/wav
file_num=$(ls -1 --file-type | grep -v '/$' | wc -l)
cd ..
if [ "$file_num" -le "1" ] ; then
        DT=$(date -u +"%y%m%d_%H%M")
RECFILE=${BASEDIR}/wav/wspr_${DT}.wav
        echo recording to ${RECFILE}
        #arecord -d 114 -f S16_LE -r 12000 -t wav ${RECFILE}
rec -V1 -c 1 -t wav ${RECFILE} trim 0 118 &>/dev/null
echo "converting sample rate..."
sox ${RECFILE} -r 12000 /tmp/out.wav
echo removing ${RECFILE}
rm ${RECFILE}
echo moving /tmp/out.wav to ${RECFILE}
mv /tmp/out.wav ${RECFILE}
        echo "running decode on ${RECFILE}..."
        ./decode ${DT} &
fi


Here's my version of decode:

# Script for the K9AN WSPR decoder, by DJ0ABR
# ===========================================
# use the k9an decoder to get the spots out of the wav sound file
# the file 'spots' is used for storing all the spots and debug information
# the file wsprd.out contains the current spots in the format for wsprnet.org
# wsprdsum.out is used as a temporary storage if the upload fails

MYCALL=VK2TPM
MYGRID=QF56OF
BASEDIR=/home/pi/wsprcan

echo decoding >> spots
echo "decoding: /home/pi/wsprcan/wav/wspr_${1}.wav"
./k9an-wsprd -f 14.0956 /home/pi/wsprcan/wav/wspr_${1}.wav >>spots

# the wav file is processed, delete it (it should be in a ram disk folder if an SD card is used !)
rm ${BASEDIR}/wav/wspr_${1}.wav

# check if spots are available
FILESIZE=$(stat -c%s "${BASEDIR}/wspr_spots.txt")
echo data size= $FILESIZE >> spots
if [ $FILESIZE -ne 0 ] ; then

        # add the spots to a temporary file used for uploading to wsprnet.org
        echo add to wsprdsum.out >> spots
        cat ${BASEDIR}/wspr_spots.txt >> ${BASEDIR}/wsprdsum.out

        # upload the spots
        echo upload by curl >> spots
        # ping helps curl to contact the DNS server under various conditions, i.e. if the internet connection was lost
        ping -W 2 -c 1 wsprnet.org #> /dev/null;
        curl -m 8 -F allmept=@${BASEDIR}/wsprdsum.out -F call=${MYCALL} -F grid=${MYGRID} http://wsprnet.org/meptspots.php > /dev/null;
        RESULT=$?

        # check if curl uploaded the data successfully
        # delete only if uploaded
        if [ $RESULT -eq 0 ] ; then
                # data uploaded, delete them
                echo Upload OK, deleting >> spots
                rm wsprdsum.out
        fi
        echo curl result: $RESULT , done. >> spots
fi

Please replace VK2TPM with your call and grid square.
The crontab file:

# Start WSPR Recording at every even minute 
*/2 * * * * /home/pi/wsprcan-master/record

To see what's going on you need local email. I installed postfix and mutt for this. There's a log file called spots that shows what's going on and any decodes:

decoding
0648 -15 -2.5  14.097089 -2  K6PZB CM88 37 
0648 -20 -2.9  14.097099 -2  VK8ZI PH57 23 
0648 -24 -2.7  14.097116 -2  KD6RF EM22 37 

data size= 222
add to wsprdsum.out
upload by curl
Upload OK, deleting
curl result: 0 , done.
decoding
0650 -23 -2.6  14.097048 -2  K5XL EM12 33 
0650 -20 -2.1  14.097072 -2  AL7Q BP40 37 
0650 -19 -2.7  14.097158 -2  JA5NVN PM74 33 

data size= 222
add to wsprdsum.out
upload by curl
Upload OK, deleting
curl result: 0 , done.

So far I haven't used the ram disk but that's probably a good idea in the long term.

I also tried VisualWSPR which looks hopeful but crashed on startup for me. 

Wednesday, June 08, 2016

What's inside an SDRPlay

I love tuning around HF with an SDR display, it's great to see the whole band in one go.

The recent v0.1.20-alpha update to CubicSDR works very well on MacOS and in particular with the SDRPlay. These things just look like a black plastic box and I haven't seen any pictures of the internals so here you go:



As you see not much there, but it has 8 automatically switched input band pass filters. Full technical information is here.

It interfaces with SDR software via SoapySDR:


And works really well.