TT’s Jottings-Blog of VU2SWX

I have been  playing with the ISDR software defined radio from OM  VU2DEV ,  Ramaprabhu ( from Bangalore )for the past one week.  ISDR is a  low cost SDR for  40m band.  The radio is  performing wonderfully.    I bought 2  assembled kits from DEV and  I recommend the kits  to any one who wants  to  have a taste of SDR technology.  The  fully assembled radio is available with VU2DEV at Rs 750 ( US $15 approximately) and comes packed in a rugged metalic enclosure and with necessary  audio cable.  ( Email vu2dev  at yahoo.com for  availability,  exact pricing and shipping info. ).

The following pictures   show the professional quality ISDR  .

Indian SDR reciever from vu2dev

Inside view of ISDR

OM VU2DEV has also sent  me the schematic  diagram and component values   and  permitted me to post the same on my blog.

The block diagram of the radio is shown below. (Click on the picture for a larger view)

ISDR block diagram

At the heart of  ISDR is a 28.224Mhz  crystal which is used to create stable  oscillations. This frequency is divided by 4  using two 74HC74 dual flip flops to produce  two  90 degree out of phase  local oscillator signals for the radio.

On the RF side signals from the antenna are  filtered for the 40m band and some  RF amplification is given.  The RF signal is then mixed with  local oscillator signal using two diode ring mixers.  The resultant  signals  are   sent to a simple low pass filter to get rid of unnecessary  mixer products and then amplified.  The   two quadrature signals are fed to the mic input of  a PC sound card.  ( You need a sound card with stereo input).

The sound card is used as  analog to digital converter. The normal sound card found on your PC will have a sampling rate of 44khz ,with  16 bit accuracy.  The sampled signals are  processed digitally inside the PC using SDR software and you can hear the radio via PC speakers.   Your tuning range will be half of the PC sound card’s sampling rate.  So with  44Khz card , you can tune from 7034Khz to 7078Khz. If you have a professional quality sound card,  your milage with SDR will be better.

The circuit diagram and  component values are  given below.

ISDR Circuit diagram sheet 1

ISDR Circuit diagram sheet 2

If  you want to look at the circuit in finer detail,  download this  pdf file.   The info sheet provided by vu2dev is here .  The component values for the circuit can be found here.  T

I have successfully used  Rocky,  kgksdr and winrad on my PC running Windows XP ( 🙁 , I had to install it at last  ).  I am yet to test the SDR on linux and will update as and when I am able to do so.

My Intel  G35 mother board seems to  supports ( I am suspect )   96khz sampling via the onboard Realtech card.  Hence , I am able to tune almost the entire 40m band. Here is a recording from the  radio using  Rocky.

Update  22-9-2011
OM VU2DEV   at his morning QTH M/s Micronova Impex Pvt Limited  is making  a large number of   kits including ISDR for the benefit of the community.  You may contact them directly.  The contact email id is <vu2dev@yahoo.com>.

I have used his  JOTA transceiver  and reviver . Both are valuable additions to your  shack. He has also provided me with PCBs of his new 72 watt linear, I am planning to build them during my next vacation

Here are photographs of my shack. I have built several equipments and  circuits over the years. These pictures show the status of my shack as on September 2010.  I took them last week on a Nikon CoolPix L21 .

My shack

Another view of my shack

My Work Bench

Work Bench _ Soldering

Tuner and SWR Meter

Bitx80 My 80M Homebrewed rig

My Bitx 40 built in manhattan style

Bitx20 built on PCB

Jota Tranciever Baught from VU2DEV

VHF handies - Woxun and an old SXA tuned for Ham band

RF Probe Built by my friend Neelandan

Last week I had to visit IIT KGP and Calcutta. I managed to get a ticket at the last minute and quickly settled on Shalimar express. Most of my companions were Bengali revellers returning after touring god’s own country.
Before reaching Varkala a vendor with water bottles came. I bought a one litter bottle. Then I noticed that most of my Malayalee co-passengers were buying water bottles where as the Bengalis were travelling with cans filled with water. The train reached Chennai next morning and most of the Mallu crowd was gone. Lot of people from Andhra and Orrisa came in. Almost all had water bottles filled at home.
Many of them were refilling the bottles at stations. The remaining Mallus on the train were buying bottles. When the train reached Vijayawada there was a small queue in front of a counter which displayed ” Bring in your bottle and fill at Rs 1 “. People were seen confidently using public taps in North India. However, in Kerala you can see passengers buying packaged mineral water and throwing away bottles. Is the quality of our water so low? Or is it just another Mallu prevention ?
Anyway on the way back home, I filled two bottles form IIT guest house and carried with me. It lasted till Vijayawada. I refilled them at ” Bring in your bottle and fill at Rs 1 ” and used it till Chennai Egmore. I had plenty of time at Egmore waiting for my connection train to Trivandrum. I looked around for a tap and found out one. But I turned skeptical at the last moment and bought a bottle.
I have a few questions now. Why the railway is not providing quality drinking water through public taps on the platform? If you look out of a compartment you can see thousands of empty water bottles on both sides of the track. Why we are not bothered about the environmental problems it creates ? How good is the packaged water that we get on the railway?
Look at any public function or TV discussion , you can see mineral water bottles on the dais, even though no one drinks. It is a fashion for even small meetings in our college to place few bottles of packaged water in front of the guests. When did this trend begin ?
Packaged drinking water is available in almost all shops in Kerala. It seems the next generation will be afraid of drinking well water.

I took a session on recycling old PCs with LTSP at   barcamp kerala 7 last Sunday.  Even though I am associated  with the organizers of barcamp ever since its inception in Kerala, I could not attend any of the previous ones due to various reasons. So I was a bit skeptical about the kind of people I may meet. Also, this was the first public lecture I gave after assuming charges of Principal College of Engineering Attingal. I  conveniently hid this fact from the audience suspecting that my job profile might overshadow the geek in me.

I was picked up from home by Kenney Jacob at 5.30 am  and we stated our journey to Changannasery on a TATA VISTA . The car was fantastic with GPS can other gizmos . A few of Kenney’s colleagues were also present in the car. We reached the  venue around 8.45 to find that the  gates of the Krishtu Jayanti college were closed. Kenny made some frantic telephone calls and finally we were asked to enter the college via  the  gates of a Catholic church.

There were around  70 guys in the hall. There was some initial hiccups and the  sessions took some time to start . I missed introductory remark by Kevin as I went to the nearest tea shop for a quick dose of coffee. The next session from Prassed Pai on 3d graphics programming was good and reminded me of my PG classes at CUSAT where we did all the shading and drawing algorithms. I think most of the audience was clue less about the topic.
The next session    Building Complex Website the Drupal Way from  Fredrik Jonsson? was   enlightening.
The third  session on Media by Kenney Jacob initiated some interesting discussions among the audience. Some of the participants expressed the fears about corporate media  manipulating facts .
Next was a cake cutting session . Some one suggested Fredrik Jonsson’s name for the event and every one clapped  when he cut the big cake sponsored by   ayruz web holdings  . Later I had lunch at a local teashop .
I took the first session in the after noon. My Idea was to set up my laptop as ltsp server and net book as the client . Then project the client to  the  big screen and start the presentation on the client.
The Sharp projector  at the venue was behaving erratically. It showed only half of the screen. I had to change instantly to the white board and start writing.  I briefly explained the  LTSP  with a figure that I drew and later on moved the projector to my laptop. The presentation was shown after explaining things with a white board.  I think half of the audience got confused by then.
The next session from UST global was  quite boring. I think such PR crap should be avoided in barcamps. I missed the session by Binny VA as I went out for a tea again.

The last session on linux devices was good,  but Praseed Pai  seemed to be the only person understanding it.
Finally, Fr. Abraham Mulamootil made a surprise appearance. I think it is the first time a catholic priest is seen publicly in a bar(camp). Any way he seems to be the only geek in the church.
The entire event was wound up around 6pm.
The facilities at the venue were pathetic.  No one from the college turned up. There was no net connectivity.  The wifi link of the college was running but their firewall was preventing outgoing net  request. Hope the next barcamp at Thiruvalla will be better and more interesting.

As I travel frequently  in connection with my official and no-official engagement, my internet presence is disrupted. I have tons on mails and rss feed entries to be read after each journey. I was thinking of buying a netbook.
I recently bought a Toshiba NB200 netbook at a discount rate from my cousin. It came with 160 GB hard disk 1GB RAM, intel atom processor and Windows XP was pre-installed.
The first thing I did with the netbook was to remove windows. I installed ubuntu netbook remix 9.10, All the hardware except sound was instanly recognised by ubuntu. My next task was to  make it internet ready. I looked for various solutions like evdo from BSNL , netconnect from reliance etc. They all looked costly.
Finally I decided to go in for GPRS connection from BSNL. I  am already an unlucky owner of Nokia N72 , which is recognised only from windows. Fortunately the GPRS modem on N72 is accessible from linux . Here is what I did with my BSNL prepaid  phone connection to get it ready for my net book.

1) Enable GPRS on the phone

The GPRS can be enabled on BSNL connections by sending an SMS to  53733 with the following  word.  GPRSPRE. (I use a prepaid connection). They charge heavily    for GPRS usage 10 paise per KB.  However, they have some schemes which provide unlimited Internet access.
If you are a sporadic traveller, unlimited gprs access  for one day can be availed at Rs.20. For ardent travellers, an unlimited connection for one month can be subscribed at Rs 230. For availing the special schemes, you have to send sms to 53733 with the word GPRS20 (or GPRS230). You need a minimum balance of Rs 75 in your prepaid account for availing GPRS20. Once you send the sms,BSNL will ask you to confirm the scheme by sending another sms with GPRS20Y to 53733. (Sometimes it takes an hour or so  to get back the sms asking for confirmation. Being an Indian, you have to be patient.)

2) Configuring the Modem.

This was rather easy as my N72 GPRS modem was recognised as soon as I plugged the data cable.
I verified its presence  by looking at dmesg output on a terminal.

I installed wvdial from the ubuntu repository .

$ sudo apt-get install wvdial

Next, I ran the following command.

$ sudo wvdialconf

It created a minimal configuration file for wvdial  /etc/wvdial.conf.

/etc/wvdial.conf was then edited as shown below.

[Dialer Defaults]
Init1 = ATZ
Init2 = ATQ0 V1 E1 S0=0 &C1 &D2 +FCLASS=0
Init3 = AT+CGDCONT=1,”IP”,”GPRSSOUTH.CELLONE.IN”,””,0,0
Modem Type = USB Modem
Modem = /dev/ttyACM0
Baud = 115200
Dial Command = ATD
Phone = *99***1#
Username =9194461xxxxx
Password =9194461xxxxx
New PPPD = yes
Stupid Mode =yes

Use your phone number as username and password. I entered the phone number including the country code as shown above. Also look at the Init3 entry. If you are in south India, you can use the above line. For other regions look at this page.

Now you can access internet by dialling out using wvdial.

$ sudo wvdial

The internet speed is reasonable.

I am posting this from Venad Express on my way back from Model Engineering college where I delivered a lecture  on free software. The netbook was really handy for the presentation too.