The mcHF HF SDR Transceiver - 9

The Microphone Mod

Below are the pics of my microphone mod which I did for using it with mcHF.

I had bypassed all the circuitry inside the mic and re-wired it so that the ptt and microphone directly goes to the rig.

The microhone(HM-158L) is typically for VHF handies and came with 2 pin connector. I replaced the connector with a stereo connector which is the connector required for mcHF.

 

 

Made use of the tracks available in the PCB removing the unwanted components.

 

You can see the inbuilt speaker in the center and the mic on to the bottom right in this picture.

Later on, I had removed the inbuilt speaker and moved the Electret mic there, which gave better performance.

The mcHF HF SDR Transceiver - 8

As I said in my previous post, my mcHF had been transmitting with 10W power after installing the new Mitsubishi mosfets. With the current goal met, a new target came into place. 
More POWER :). 

Here is the rear view of my mcHF RF board.

One of the modifications that was being discussed in the mcHF yahoo groups was for the T7 modification(Modification of the output transformer in the PA). 

The existing transformer with 2:3 turns wound on BN43-202 core is not matched and is not efficient as it should be. The turns ratio needs to be 1:4 if you see output transformers in other push-pull amplifiers which use RD16HHF1 as the final mosfets. One solution to this is re-winding the T7 transformer to minimize the flux leakage. There is a proven way to accomplish this task.

Instead of using 1 binocular core, we use 2 and the primary will be wound with wire of maximum thickness. An innovative way of doing this is using the braid of coaxial cable-RG58 for winding the primary. Details of this can be found in mcHF Yahoo groups.

Below is the photo of the modified T7 transformer for the additional power output.

After few mods including the above one, my mcHF is now putting out a decent 15 W on 7 MHz :) .

The mcHF HF SDR Transceiver - 7

It has been quite a long time since I posted anything on this blog. Reason being, investing too much time into mcHF modifications whenever ever possible.

Here is one video of my mcHF on transmit.

Thanks a ton to VU2ELJ for the QSO.

The mcHF HF SDR Transceiver - 6

And finally... the mcHF is transmitting...:)
Both Vimal and myself had ordered the MOSFETs from multiple vendors and one among them reached me last week. I replaced both the IRF510s which I had soldered temporarily with the newly arrived RD16HHF1 mosfets. Connected the SWR/Power meter, dummy load and pressed the PTT and whistled. The meter showed close to 10W in Full power mode and showed almost 5W in 5W power setting.

And now I can say the transceiver is complete. Meanwhile I also re-wired an ICOM microphone to work with my mcHF. Shall post some transmitting videos soon. :)

The mcHF HF SDR Transceiver - 5

Pathetic service from IndiaPost - Shame on you IndiaPost

It had been more than a month since I ordered a pair of mosfets from Aliexpress. The package arrived in India and was sent back without even me knowing of it. 

The package was sent from Beijing on May 16. Chinapost packages are handled by IndiaPost after it reaches India.  On June 16 2015, it had reached up to my city, and I was available at home for the whole week to receive it . No postman came, No calls received, it was sent back to China with out my knowledge. When inquired in customer service, they even don't know why it was sent back. Below is the tracking information.

I have opened a dispute in Aliexpress for getting the refund and also filed a complaint in IndiaPost website. 
Moral of the story: 
IndiaPost = Zero Accountability.

The mcHF HF SDR Transceiver - 4

As I am still waiting for the MOSFETs to arrive, thought of sharing some technical details on the mcHF.

Features:
  - A standalone[PC not required] compact embedded HF transceiver
  - 2 MHz to 30 MHz Continuous frequency coverage
  - Operates on USB, LSB, AM and CW
  - 2.8 inch color TFT LCD
  - Four rotary encoders and 17 buttons for easier operation
  - Fast and fully electronic RX/TX switching
  - Two USB ports – for PC control and external keyboard
  - Two temperature compensated oscillators/clocks
  - Four digital filters – 1.8kHz, 2.6kHz, 3.6kHz and 10kHz
  - Built in Iambic Keyer that supports Mode A and Mode B
  - Large 48 kHz spectrum display
  - Variable tuning steps

Hardware Specification:
1. Processor - STM32F407 from ST Microelectronics.

     - Core: ARM® 32-bit Cortex®-M4 CPU with FPU

     - 168 MHz, 32 bit
     - 100 Pin package

     - 3.3 V operation

     - 1 Mb flash memory

     - 3x12 bit A/D converters

     - 2x12 bit D/A converters

2. Codec - WM8731 from Wolfson

     - 28 Pin package
     - 3.3 V operation
     - ADC, DAC sampling frequency - 8 kHz to 96 kHz
     - ADC SNR 90 dB
     - DAC SNR 100 dB

3. RF Power Mosfet
     - 2x RD16HHF1 RF MOSFET from Mitsubishi

4. Local Oscillator
     - Si570 from Silicon Labs
     - 10 MHZ TO 1.4 GHZ I2C PROGRAMMABLE XO/VCXO
     - 8 Pin SMT
     - 3.3 V operation

5. SN74CBT3253C Tayloe detector as a direct conversion mixer

The mcHF HF SDR Transceiver - 3

In my last post, I had mentioned about the issue of fuse getting blown off. The cause of the problem was traced to PA stage and I did a workaround to skip the problem and continue with the receiving part. As a workaround,I had removed the RF Choke through which power was being supplied to the final PA stage, so that the PA stage was isolated.

Now that the receiving is working well, I started thinking on the first issue i.e blowing fuse issue. This time there were lot of suspects in my list :). The output transformers, the SWR transformers, driver transistors and many others. 

The problem is, when ever I provide dc supply voltage to the PA stage, the transceiver draws a hell lot of current and the supply voltage reduces to as low as .68V from 12V. And the transceiver won't power on. And if the power connector is removed, it blows off the fuse as well. 

There can be many possibilities for this issue like wrong connection in output transformer, shorts in any of the transformers wound on Binocular cores, High bias voltage reaching the MOSFET gate which in turn could conduct all the current from Drain to Source, any damaged smd components in the PA stage and many others.

The first thing to be done was checking for shorts in output transformers after removing from the PCB. But couldn't find anything wrong in the transformers. Next I checked the bias voltages to the MOSFET gates which came from the LM2931 IC. That too looked OK. 

What now?? There could be some RF voltage coming into MOSFET gate which is driving this MOSFET crazy. The RF voltages will go undetected in DMM(Digital Multi Meter). So I connected an RF Probe and checked for the existence of any RF voltages in the MOSFET Gate. RF voltage in Gate=0V. So these experiments continued. I never suspected the PA MOSFETs , because they were bought from ebay.com from US and brought to India by one of Vimal's(VU3CPE) friend. (Vimal a friend of mine and myself are sourcing the components together and building the mcHFs individually)

Also Vimal had tried replacing his MOSFETs with one which was bought sometime later(We had bought the MOSFETs twice, because of the first package getting lost during transit and later on getting back the same. It's a long story:). Anyways we ended up having two sets of same MOSFETs, Toroids etc.)

So all these things made us believe that MOSFET is not the culprit. 
Experimented many things, but all resulted in high current drawing and shorting the supply voltage. With all the possibilities exhausted, I turned to MOSFET. The MOSFET used are two numbers of RD16HHF1 made by Mitsubishi. I took out the MOSFET from the circuit and tried to check the Vgs vs Id(Gate voltage vs Drain current). 

Lets go through some basics of operation of a MOSFET.
MOSFETs are nothing but valves,in which the current flow can be controlled by varying the Gate voltage. So till the Gate voltage reaches a certain value, the MOSFET will remain non-conducting. This value is know as the Threshold voltage or Vgs(th) or simply Vth. Usually this would be somewhere around 3-4 Volts. That means till you supply at least 4 Volts to the Gate, the MOSFET will remain off. This region of operation is called "Cut-Off" region. Once you increase gate voltage above 4 Volts, only then the MOSFET will start conducting. 

Back to our MOSFET experiment. I needed to check how our MOSFET was behaving in the cut-off region, i.e. when Vgs<4v. I had to set the Vgs to '0'. So shorted the MOSFET Gate to the Source and connected it to a negative of my power supply with voltage set to 10V. The power supply is a small one capable of sourcing only about 1.2A. The DMM was kept connected to the power supply. As soon as I connected the positive lead of the power supply to the Drain, the supply voltage dropped to 0.68V almost shorting the power supply. Repeated the experiment, this time with the DMM connected as an ammeter in series to check the current draw. The whole of the current which the power supply could source was flowing through the MOSFET. I couldn't believe this :) there seems to be no effect of the Gate Voltage(Vgs) on the Drain current(Id). And this confirmed that the MOSFET was the one shorting the entire circuit.

 Meanwhile, Vimal(VU3CPE) got his MOSFETs replaced by sending his completed SDR Tranceiver to VU3GEK and it is transmitting fine now. The video of the same is available in YouTube. Also Vimal is getting a few number of RD16HHF1 for both of us from VU3GEK, so I m waiting for the new MOSFETs to arrive. I am experimenting with IRF510s till I get the RD16HHF1s. The Drain, Source pins are reversed for IRF510. I have used IRF510s in past for the BITX transceivers that I had built. The IRF510 being a switching MOSFET, will nowhere match the performance of RF MOSFET RD16HHF1, but still, something is better than nothing...at least for the time being. :)

The mcHF HF SDR Transceiver - 2

There had been a long gap after the completion of the mcHF UI board to start with the RF board soldering. Mainly it was for the time required to source all the components needed for the RF board.So to cut it short, I started with the RF board soldering and completed soldering about 90% of the components using hot air soldering. I left the smd inductors, relays to be soldered in the end using conventional soldering iron since hot air would melt their plastic bodies. And the hand wound inductors were the last parts to be soldered into the RF board. All done in about 2 weeks. Now, the real challenge :) Testing it and making it work.

Connected the board to a limited current power supply. And pressed the on/off button. But nothing happened. It didn't power on. :((Before soldering the RF board components, it was working..see the photo and video in my last post.)Found that the SMD fuse in the power supply section was blown out. And the worst part is, I didn't have much fuse left for experimenting. There was a Schotky diode for reverse polarity protection. It became my central point of suspect along with few others. After taking the suspects out of the RF board, it was found that they all were totally innocent in this issue.

The next suspect was the transmit side with the PA consisting of 2 nos of RD16HHF1 MOSFETs rated for 16W 3-30MHz, Torroids, LPF, BPF stages, Antenna switching etc. So the best thing to isolate the stage was to cut the power to that stage. The 12V supply comes to this PA stage through an RF choke RFC8 which is a single turn 24SWG copper wire through a small binocular core(BN43-2402). I wanted to make the receive part working before going for the transmit. I removed RFC8 cutting the power to the PA stage. Replaced the blown out fuse with a new one.And there it is, the Rig powered up showing the spectrum display. So the fuse blowing issue was isolated to the PA stage. Thought of checking it later, once the receiving is found to be working.

Connected my speaker...And guess what...there was no audio at all.I increased the AF Gain to max, RF Gain to max. But still no audio.
I traced through the DC voltages for the ICs in the receive stages and everything seemed to be fine. Checked for any soldering bridges in the processor for the digital signal input/out put pins. But that too seemed fine. Checked CODEC, Switching IC, Speaker amp. Again here my suspect became the SMD Audio amp, the LM386M-1.
The DC voltages seemed to be fine. To check if the Audio amp was working, I isolated it from rest of the circuits by removing the coupling capacitors. Connected audio from my Samsung Tab to the input of the LM386M-1 and played a song. There came crystal clear audio from the speaker. And there goes LM386M-1 out of the suspects list.

Next was the Codec IC, WM8731. After removing the isolation made in the LM386M-1, I did the same thing with the codec IC. Isolated the input to the codec and connected the audio from my tab playing an mp3 at low volume. But this time there is no audio from the speaker. With this I became doubtful if the  codec's working.The analysis continued for two evening sessions. On the third evening,I noticed a strange thing which went un-noticed in the initial analysis.
There was a short between pin 15 and 16 which should not be the case according to the schematic. Across these pins are connected, C22 and C23. C22 being an SMD Tantalum, I thought it must have been blown out. I desoldered it and the short was still there between pin 15 and 16. And the pulled out tantalum was also not shorted. Removed C23 SMD capacitor and the short between the pin 15 and 16 is there no more. :)

Even though the pulled out capacitor didn't give any short while continuity check, I replaced it with a new one after cleaning up the board. May be there was some un-melted BGA soldering paste(mixture of lead and flux in the form of paste) under C23 which lead to this short. Anyways, I didn't go for further testing it. I went ahead with connecting the rig to power supply and then switched it on.
:):):)

The rig came up with audio in speaker :). Connected my 20m antenna to it and searched around the band and rest you can see it in the below video :).

I have built many conventional radios in the past and I feel that the happiest moment is when,you hear some one talking from some where in this world, through the radio that you newly built. And this time also it was no different with this cute little QRP SDR.

The mcHF HF SDR Transceiver - 1

This is one of my current projects still under construction.
I started building it couple of months ago and is still under progress due to limited time availability.

mcHF is a standalone Software Defined Radio designed by a ham from UK, M0NKA (Chris) which is getting popular at an unimaginable pace. Unlike SDRs which requires a computer to operate, mcHF being a standalone SDR doesn't require a computer to operate with. It has its own processor, ADC, DAC etc. It has got a wide coverage all along from 3.5 MHz to 30 MHz and is capable of delivering 10 Watts of output power.

Coming back to the basics of Software Defined Radio, I have seen many getting confused between a Software defined radio and a Software controlled radio.Software controlled radios are nothing but the same analogue radios that we have been used to, but with a digital interface. Software is just used for controlling various functions of the radio. The functions like digital control of VFO, AGC, RF gain, AF gain, LCD display to show the frequency, SWR, power etc are some examples.

But on the other side, the working principle of a Software Defined Radio(SDR) is completely different.Here the software itself has been used to model the radio. In layman's terms, you could say that the building blocks that make a radio are implemented by Software program. Changing this software program can change the working of the radio completely. Say you have a software defined radio built to receive FM signals. You could just change the software inside to make it a AM, SSB or a CW radio without any changes in the hardware.

Most of the SDRs after down converting(some high end SDRs are exception) the receive frequency, they sample the signals i.e. they convert it to digital format consisting of just numbers. Digital wave forms which are nothing but a series of numbers can easily be processed by the processor. After this point, it is pure mathematics which does our job with the help of DSP. All the basic processes inside a normal radio like Mixing, Filtering, Noise reduction etc can be achieved in digital world with out much effort.

back to mcHF :)

mcHF consists of 2 boards, UI Board and RF board. 
The UI board mainly consists of the processor (STM32F04), the codec(WM8731), the TFT LCD (HY28B) and other UI related components. The project is not available as a KIT. As of now, the boards along with the LCD can be bought from Chris(M0NKA), the designer of this radio. Below is the website of M0NKA where the order can be placed.

http://www.m0nka.co.uk/

And the components, in India can be sourced from 

http://in.element14.com/ 

or 

http://kitsnspares.com/

Few parts like the RF Power mosfets, torroids etc will have to be sourced from abroad. Both the boards are SMD double sided boards. Do not fear away from this project all because it is SMD. Both the boards can be assembled using a normal soldering iron following any of the many SMD soldering styles or may be by using a Hot Air soldering iron as I did. There are lots of videos available in Youtube showing different soldering techniques.

I would suggest not to take this project as your first Homebrew Transceiver Project since it is not a plug and play kind of kit. But if you have built any analog radios before, mcHF build will amaze you for sure :).

Below is the YouTube video of my mcHF UI board coming to life few months ago.

Ham radio and me

To introduce myself, I am  an 
Electronics and Communication Engineer by Graduation,
Software Engineer by Profession
and a Ham Radio Homebrewer/Operator by Passion.

I cannot remember when I started loving this amazing thing called Radio. If I look back towards my childhood days, during early 90s, I had always been loving radios and I still remember seeing walkie-talkies used by the police used to leave me wonder struck.
I used to dream to possess one of those walkie-talkies. Those were the days when there were no mobile phones and not even in your distant thoughts you could imagine that such a device would come in future to the hands of a common man.

During my childhood days, my uncle who was doing his civil engineering at that time, used to build electronics stuffs like Audio amplifiers and home-theaters. I used to be his assistant while soldering the electronic boards and I enjoyed it.This gave me a lot of exposure to electronic components, soldering and all those basic stuffs. And all these helped me in doing many hobby electronics circuits myself during my school days. Also I had a chance to build many basic AM,FM receivers and transmitters of low power levels during those days.

And this same love towards electronics and radios took me to pursue my Engineering in Electronics and Communication at National Institute Of Technology Calicut (NIT Calicut). 
Engineering provided me a different perspective of electronics, a mathematical one. Considering today's educational system, an electronics hobbyist and electronics engineer are at opposite banks of a river. But the home-brewing activities and the passion for radio circuits helped me bridge the two.

Even though I never kept away from home-brewing or electronics circuits, I could not spent much time for applying and getting a HAM licence during my college days.
Once I started working after completing my graduation, I started spending serious time into home-brewing after office hours and took the time out to get my license and thus became a licensed Amateur Radio Operator with the call sign VU3LTB. Till I got a license, I never got a chance to meet any HAMs in person and it was only me and my circuits. The license gave me a chance to meet and socialize with other Hams.

This being my first blog, I would like to thank my Ham friends who had suggested to start this blog and also  Ham friends who have been encouraging me for my home-brewing activities. I would also like to thank VU2LVJ, VU3CPE, VU2SCE, VU3ARP, VU3MOG, VU3MPK, VU2KBX, VU2SVF, VU2LSW, VU3SMZ, VU3ISJ, VU2UMX, VU2RZA, VU2YNT and the list goes on.

I hope more articles would see light through this blog.