Homebrew Kits

LC Meter

This one is a small useful measuring device which would help you in homebrew projects. Usually it is difficult to find a commercial meter which can measure the range of Inductance and Capacitance that we HAMs need. If you are involved in some RF ameteur radio circuit homebrewing, then this tool would be of a great help as it has been for me. I had been using this circuit constructed on a general pcb (vero board) and using it for past few years. And this had been helpful to me in most of my homebrew projects including BITX20,BITX40,MCHF and many more. So I thought of printing a commercial quality PCB from some fab house here. The PCBs are ready now and below are the photos.

The best thing of having an LC meter in hand is, you could wind the coils on any former or ferrite without worrying about the number of turns or the material. Just wind it on any former and measure it . Also you could measure the capacitance of unknown gang capacitors.

Also I have made available the PCB along with the complete set of components as a kit. For enquiring availability please drop a mail to me at vu3ltb at gmail.com. Fully assembled ones are also available.

Update Jan 2019-
Pics of finished LC Meters in Aluminium Box.

 

The mcHF HF SDR Transceiver - 10

And finally...this is what you get :)

The mcHF HF SDR Transceiver - 10

And finally...this is what you get :)

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. :)