VU2HMY TRX Circuit - Construction Ideas

This is my first attempt at homebrewing a transceiver circuit and the first experience with the construction of an SSB rig. I had previously constructed many small CW and AM rigs including the VWN QRP and many other experimental circuits.

I recently got my license renewed and I was very happy with this. I have not been on the air for some time and so I decided to homebrew my all indigenous tranceiver. There were many circuit ideas and TRX circuits in front of me and I chose VU2HMY circuit as I was told it was quite easy to complete and operate. I am taking this time to go through a step by step construction presentation of the VU2HMY circuit. I am also getting further construction guidance from Anil Kumar VU2JQX who is a friend of mine in Trivandrum.

I had ordered for a circuit board by contacting Dr. Rajasekar VU2HMY via phone and got excellent communication from OM Dr. Rajasekar. Within 2 weeks of ordering the board, I got my circuit board through the courier post. To my amazement I got some of the Xtals included with the circuit board and I was relieved from the job to peak up the SSB band pass as all the Xtals were matched and now I only have to wire the other stages. I immediately procured all the components that are necessary for the construction of the rig for a good start.

VU2HMY TRX Project:-

I decided to start with the power supply and the audio sections first for the construction of the TRX project before going through the other sections. I already had the switched power supply with 9 volt and 12 volt range.

VU2HMY circuit board and the necessary components for building the TRX











The wiring platform that I have is a small one and so most of the tools I have to place it closeby.

A closeup view of the board and the components.






Audio Stage:-

The audio is wired around the LM380 audio IC. It is a 14 pin IC and is expected to give around 4-5 watts of power to the speaker output. As you can see all the components that I have wired around it. First I soldered the IC base in position on the board and then after soldering all the related components, I inserted the IC into its base. I tested the audio and it did give a good sound output to the speaker. Then I soldered the BC548 into place, which was supposed to be the audio predriver stage and then the audio filter stages respectively and tested it again and everything worked fine. The audio output terminals were to be terminated with the connectors that I found it difficult in procuring, but then I could get it from an electronic shop. You can also see the other IC bases that are soldered to the board.

As I was a little QRL the project is a bit slow but my enthusiasm for the project keeps me going on for completion of the project and I hope to finish the other stages in time. The next stage that I am planning to go through is the product detector/balanced modulator.







The audio side of the TRX consists of the LM380 IC, the audio predriver and the filter stages.







 Product detector Stage:-

 I just soldered my product detector stage, built around the TA7358 IC. The circuit also has the carrier oscillator stages designed within the IC, only those passive components that are needed to be connected externally through the PCB. The frequency for USB and LSB operation are produced by 2 x-tals both above and below the 10 Mhz frequecy through switching. At the first instance my product detector was not working perfectly even after many trials, so I am suspecting a need for an IC replacement. Hope to rectify it later though!

The product detector stage using the IC TA7358.











In the meanwhile I wired the other stages that are necessary for the DSB signal generation which includes the mic amplifier stage and the band pass filter stages. Also completed the CW side tone oscillator on the audio side. Hope to start the mixer stage after this.

Here after a while with some QRLs and other issues. Did some stages during the time being including a product detector, an external audio amplifier to improve the audio level, and a VFO.

 


                    
                                     External audio amp

 

                                    Power supply




  

                  

                                    Product detector

 

            



                                        The VFO

An Amateur Radio Ham

This is my first experience with amateur radio as a scientific hobby.

I had the craze for amateur radio when I was a schoolboy around 1984. I used to listen to sounds and music on the radio from distant stations and wondered where this was coming from. At that time I had a Sony band-spread type receiver and it had a wide band spread unlike the crowded band in some other ordinary receivers. I used to tune to weak signals and tried many different techniques with the antenna and trying many different types, shapes, and arrays to receive the very weak signals intelligibly. This became my everyday activity during those times. I tried many different types of receivers even from relatives homes and tried to listen to the signals and compare it with mine. I was curious to know how the unseen signals are received by the radio and was reproduced. Later it became my quest to know about that and the theory behind that. Later I came to understand that it was the function of small devices in the radio and when the power given, these devices were functioning to convert the radio signals into beautiful voice and music.

I then tried to experiment with the electronic components when I set my hands on the BC reciever first and did all sorts of tricks and tweaks. I was not able to get a performance beyond a particular level. I did try to collect as many literature about the functioning of the radio even from the encyclopedia and understand its theory and principles. From there I got some circuit and drawings of the oscillator circuits and amplifier units.

During these times I could not give more time to spend on radio because I was doing my pre degree program and the exams and had to complete it. So for 2 to 3 years I was not able to involve in any type of radio-related activities. After those years of studies I was able to get into a medical degree program and that I was able to study a subject of my interest. During that time, the thought reemerged in my mind and my curiosity to know more about the functioning of the radio. This was the time when I came to know about the Trivandrum Amateur Radio Society and later joined the club. The club was interesting with its founding member VU2TF and VU2KGB and other famous personalities and the varied activities. I used to attend the meetings of the club on a regular basis. Now I was understanding more about the radio, its functioning and beyond the radio into the higher end of the spectrum into microwaves and lasers and gamma rays. I learned a lot about satellite communication and communication through space and digital communication on HF with the use of computer on modes such as packet, AMTOR etc.

Although I was more involved in the radio and had got better knowhow about its construction and various circuit ideas, I could not do any further activities in this hobby because I was not licensed. The licensing is a must for even testing or possessing of any kind of radio equipment. Now I began to study Morse code and the rules and regulations for obtaining a license. In the beginning I was not able to get any help or guidance for the preparation of the exam. The only info I got about the exam was that I have to submit an application to the WPC wing in the DOT and that I could write the exam at a nearby Wireless Monitoring Station. I did not have much idea about the nature of the exam or its conduct. So with very little help or guidance, I studied Morse, electronics theory, and the rules & regulations. I filled out the application form and did all that is necessary to undergo a formal test for obtaining a wireless license. I appeared for the exam at the Wireless Monitoring Station, did well at the exam, and passed out the exam. I was very happy to obtain a wireless license grade 1, which I am able to hold to this day.