Saturday, November 22, 2008

HMY2K8 - A multiband HF transceiver :

By Dr. R. RAJASEKHAR, VU2HMY



TECHNICAL SPECIFICATIONS :
Frequency coverage: Ham Bands
3.500 - 3.600 M.Hz ( 80 M )
7.000 - 7.100M.Hz ( 40 M )
14.000 – 14.350 M.Hz ( 20 M )
21.000 - 21.350 M.Hz ( 15 M )
28.000 – 28.350 M.Hz ( 10 M )

Frequency control :
Ver. 1: Direct Digital Synthesizer (DDS) with 1 Hz step continuously variable VFO with 20 memory channels. 2 line LCD display. Dual VFO, Split , RIT, Key pad /rotary encoder for frequency entry.

Ver. 2: 5 Band Heterodyne VFO with PIC frequency counter to reduce cost of the project.

Receiver :
Single conversion receiver with 10.000 M.Hz Cohn filter.
Low noise figure, 2.2 K.Hz SSB band width, 1.5 W audio O/P.

Transmitter :
RF O/P - SSB - 90 W ( DC PWR I/P )
CW - 60 W ( DC PWR I/P )
Built in CW side tone, CW delay, pwr meter, MOS FET Push Pull PA.

Dimensions :8.5 X 7 X 4.5 inches

Genesis :
Being a home brewer I was hesitated to buy a commercial HF transceiver soon after getting my ticket in1988. Even my guru, late T.K.Seshandam VU2WC was not allowed me to do so. But he was kind enough to give me a set of pcb’s of VWN QRP TX . I was successful to come on air with VWN QRP effectively along with L board RX on 40M. Those days are really good for HF communication. With low band noise, excellent propagation conditions we could work hours together daily on 40 M with 7 W AM signals. After that I have homebrewed RM96 and ATS1 and came on air effectively with SSB signals on 40 M. Even though there is a feeling of missing a lot of activity on other HF bands Viz 20 M, because all the above rigs are mono banders. If I want come on other band I have to construct another rig of same circuit! Then I could get a used ICOM - IC720 commercial TRX. It worked well for about 6 months and gone QRT. I just sent it to few service centers and was not able to get it repaired due to the non availability of spares for PLL & Logic boards. Then I secured one BEL524 in dead condition and able to repair it and came on air on all HAM bands with an home made out board DDS VFO. But servicing such surplus equipment is not that much easy due to their concealed and modular construction. Then I was thinking of home brewing a multi-band SSB/CW TRX using indigenous components freely available in VU land. I searched for the circuit schematics even on the internet. But ….in vain! Then I could download and made simple 40 M band SSB TRX circuits.

Using bilateral switching technique using switching IC 74HS4053 by KD1JV using NE602 and PY2OHH using TA7358. Both performed well and gave me good results on air. But the cost of NE602/SA612 is around Rs.300/- ++ and its rare availability in VU land, whereas the cost of TA7358 is Rs.15/- and freely available.

Finally, I was decided to design a multi band SSB/CW TRX using Toshiba IC TA7358 with band switching using diode switching arrangement which can give 90 W DC PWR input from 80 to 10 Mtr bands. I have incorporated CW delay and side tone for easy CW operation. I have designed pcb (measures 7 X 3.5 inches) lay out using EXP PCB design soft ware and printed the board which accommodates all stages Viz Bal. Modulator/ demodulator, RX/TX mixer, 5 bandpass filter, 6 pole Cohn filter, Tone circuit for CW, CW side tone, mike amp, audio amplifier, transmitter driver and TRX change over. I have used home made DDS VFO using up-conversion to cover 80 – 10 M bands. In other version a pre mixed heterodyne VFO has used to minimize the cost of the rig. I hope this tiny rig shall meet all the demands of an average VU ham with all its sophistication at reasonable cost.

The circuit :
The circuit is simple and strait forward. IC1 TA7358 is used as RX/TX mixer, IC2 TA7358 is used as Product detector / Bal. modulator and IC3 as a bi-lateral switch to switch both the ICs, IC1 and IC2 to particular inputs / outputs in transceiver operation by applying DC voltage in Key down / press of PTT condition.

Receiving chain :
The incoming RF signal is amplified in broad band RF amplifier and fed to the band pass filter by applying appropriate switching voltage from the band switch from front panel. The strong local signals can be attenuated by VR1 from front panel. Here the signal is filtered in the band pass filter and fed to IC1 TA7358, RX mixer through the switching IC, (IC3 sec A). Here the incoming signal is mixed with local oscillator signal (VFO) and converted to 10 MHz IF frequency and fed to the SSB filter (6 pole 10 MHz Cohn filter) through switching IC (IC3 sec B) and fed to IC2 Product detector through switching IC (IC3 sec C). In the product detector the signal is beat with Carrier oscillator signal to get resultant audio signal which is further amplified by transistors Q2 and Q3 and sent to audio amplifier IC4 LM380 to deliver sufficient audio from speaker. The AF gain can be adjusted by the potentiometer VR3 (VOL) from front panel.

Transmitting chain :
Voice received by the condenser microphone is amplified by transistor Q4 and sent to IC2 Bal. modulator. Here carrier frequency is modulated and 10 MHz DSB signal is produced and further amplified by Q2 and fed to the SSB filter through switching IC (IC3sec C) to eliminate unwanted side band. The mike gain can be set by the preset VR2 and appropriate side band X-Tal is selected by the mode switch SW 2 from the front panel. The 10 MHz SSB signal from filter is fed to the TX mixer IC1 through switching IC (IC3 sec B) and mixed with Local oscillator signal (VFO) to get required transmitted frequency. The signal is further amplified by 2 stage broad band RF amplifier and sent to band pass filter through switching IC (IC3 sec A).

Appropriate band pass filter is selected by applying +12V to the switching diodes from the 5 way band switch SW3 from front panel or from logic out put from DDS VFO in case of using DDS VFO. Few milli volts of RF of TX signal from band pass filter is further amplified by 3stage broad band HF driver amplifier for about 1 – 1.5 W. The driver amplifier is having good linearity through 80 – 10 mts and the gain of the amplifier can be adjusted by changing the value of damping resistors R53, R54, and R57 to get adequate drive level to the final amplifier. Initially one can come on air with this 1W power and can work few stations to get reports and to align the transceiver.

VFO :
I have used DDS VFO using AD9851 along with PIC16F628 in up conversion mode to cover 80 to 10 Mtrs bands in one set and in another set a pre mixed heterodyne VFO is used to reduce the cost of the transceiver. If one wish to operate on single band, can use simple colpits oscillator such as RM96 VFO which is very stable in operation. I don’t want to describe more about VFO, because one can choose his VFO according to his taste and requirement. There are varieties of VFO circuits available in hand books or on the internet.

CW operation :
Sine wave tone around 900 K.C from an oscillator consisting of Q13 and Q14 is fed to mike amplifier through SW1, SSB/CW switch in key down condition. At the same time the side tone is amplified by IC 6 LM386 and heard in speaker LS 2. CW delay circuit provides sufficient delay for proper CW operation. The delay time can be adjusted by the preset VR7 in the base circuit of Q 12.

SSB filter :
Six x-tal Cohn filters is used for selective band width of around 2.5 K.C. Select all the six x-tals with in 100 Hz tolerance to each other to achieve proper band width and audio quality. Select carrier oscillator x-tals with + and - 1.5K.C of filter frequency for LSB and USB operation.

Final MOS FET push pull broad band amplifier :
Circuit of popular IRF 510 push pull amplifier is used for final RF amplifier which is capable of delivering of 90 W DC power input over the frequencies between 3.5 to 30 M.Hz with 1 – 1.5 W of drive. Double side glass epoxy PCB has to be used for proper operation and to achieve stability especially at higher frequencies. A large heat sink ( 6 X 3. 5 inches) with fins should be used. The amplifier draws 3 – 3.5 A for the maximum voice peak with 25V of operation. The O/P of the PA is connected to the SO239 antenna socket through change over relay contacts with a peace of 50 ohms thin coax. The O/P of the PA is sampled and the PWR level is indicated by VU meter mounted on front panel.

Construction :
Soon after finishing soldering all the components, check for shorts and solder bridges between the tracks. I have selected a cabinet of FLD (front loaded) tape deck available from electronic shops which measures 8.5 X 7 X 4.5 inches (Almost the size of commercial TRX). On front panel volume controller, Tuning knob, Attenuator controller, mode switch, band switch, key pad, on/off switch, jack sockets for PTT/MIC, Phones, Key and VU meter are fixed. The main board is fixed on the chassis and on the back panel the PA, SO239 antenna socket, relay and two fuse holders are fixed. Inter connections are done with multi strand hookup wire. 25 V line to PA has to be wired with thick wire used for car wiring capable of carrying 5A. All audio connections should be made with 1+2 shield cable and the RF interconnections are done with thin coax cables RG174 and RG58C/U. Shields with thin ms sheet should be provided for SSB filter, VFO and to the PA. PTT switch and microphone are housed in a small plastic box such as cell phone charger case. Condenser microphone is wrapped with few layers of soft cloth or sponge to avoid unwanted low frequencies entering into mike such as breath. 1 + 2 thick shield cable which is used for public address system should be used for microphone.

Alignment :
To align the receiver, the RF signal from signal generator or the incoming signal from antenna should be used. Both the coils for each band in the band pass filter are peaked by Teflon alignment tool for maximum signal strength. Then adjust the carrier frequencies of LSB and USB X-Tals for exact beat note. This completes the receiver alignment. To align transmitter, connect a 6 V low current bulb to the O/P of driver amplifier and apply power to TX line by pressing PTT or in key down condition. As you shout into the microphone or depressing the key, you will observe glow in the bulb. By observing brilliance of the bulb set the mike gain preset VR2 to adequate level. If necessary alter the values of damping resistors R53, R54, and R57 in driver amplifier to get adequate drive. Keep this level 20 % low in CW mode to protect the finals from thermal run away by adjusting CW level preset VR8. Now disconnect the bulb and connect the driver amplifier O/P to relay, with this one can work (QRPP) few stations and get reports initially.

Connect a milli ammeter in series with PA and apply 25 V than adjust idling current of MOSFETS to draw 40 mA ( 20 mA each) by adjusting potentiometers VR4 and VR5 . Then disconnect milli ammeter and connect 5A FSD ammeter and connect the driver amplifier O/P to the I/P of the PA. Now connect 50 ohms / 100W dummy load or an external antenna to the rig. By shouting into the microphone, check the current drawn by the PA. It should be 3 – 3.5 A at 25V of drain supply. If not, re-adjust the mike gain preset VR2. Too much mike gain leads distortion of transmitted signal and shift in operating frequency.

Things to remember :
1. All the resistors should be of 1 % tolerance and capacitor C6, C8, C11, C13, C16, C18, C21, C23, C26, C28, C56, C57 are styroflex to obtain stability and to avoid drift in operation. Use only 74HC4053 high speed switching IC to achieve good results especially in higher bands.
2. SSB filter should be shielded with a metal case and grounded.
3. Use 1 + 2 shield wire for audio and RG174 & RG58C/U for RF inter connections.
4. Good quality heat sinks should be used for Q8, Q9, IC5 and a large ( 6 X 3.5 inches ) heat sink for FETs. Use heat sink compound applied both the sides of mica washers.
5. Shield VFO and the PA with small boxes made with soft ms sheet.
6. Beware of static damage while handling FETs, microcontrollers etc. Ground your soldering equipment and unplug from mains while soldering such devices.
7. Use 50 ohms/100W dummy load and carry your initial testing of your rig. Don’t shout haaaalo--- haaaalo---- halo on air and create QRM to others. Identify your self on band to get critical reports and certainly these reports shall help you to improve the performance of the rig.

Component Layout :

Click on Image for larger view


Power supply :
The exciter requires 12 V / 1 A depends upon the type of VFO / Display and PA needs 24 V / 4 Amp to get maximum RF O/P. I have got 35 W DC PWR I/P even with 12V car battery and had several contacts. The following circuit diagram can be used for PSU. Use rated fuses and good heat sinks for LM7812 and 2N3055.

Click on Image for larger view

List of components :

Click on Image for larger view

Click on Image for larger view

Coil winding details for Band pass filter : Slug tuned 10 mm former (Preferably with slots for split winding). 36 SWG or thinner enamel copper wire.

Click on Image for larger view



Acknowledgements :
I am thankful to VU2RVK and VU2WMJ for their great support especially monitoring my signal and giving reports. I thank VU2RM and VU2SV for their critical suggestions to improve the final performance of the rig especially on improving CW oscillator. I also thank our UV hams VU2NR, VU2VWN, VU2RM, VU2ATN, VU2IF, VU2EM, for their great contribution of designing and publishing successful homebrew rigs and kept many hams on air.

I thank VU2PAL, VU3ITI, VU2RJN, VU2AF and all net controllers who are controlling nets for year together and keeping hams active in spite of their busy schedules.

Guardian angel of my happy HAM home, my XYL Dr. Ashalatha and my harmonics Hannu and Minnu were more keen on my academic and research activities rather than domestic chores and kept me scintillating with vigour always and never allowed any situation that would dampen my enthusiasm for ham radio.

73. Happy home brewing.

Courtesy :VU2HMY, OM Sekhar.(9704269922), vu2hmy@yahoo.co.in

44 comments:

  1. superb write up & absolutely first class homebrewing! Congratulations.
    Kevin - M0KHZ

    ReplyDelete
  2. Good, I think finally we got a good HF set with all bands from our land....

    Happy homebrewing

    VU2WSM (Satheesh)

    ReplyDelete
  3. Great Job my friend. I would like to give some inputs for enhancing the performance. Drop a private mail to my id: lkorahul@yahoo.com

    Have been working with these components for long.

    73

    Rahul VU3WJM

    ReplyDelete
  4. AWESOME!!!! Great job. Congrats.
    Pradeep, vu2pcd.

    ReplyDelete
  5. Excellent Rig OM, Wish you the very best and good luck. Would try it one day for sure.

    73
    Gaurav

    ReplyDelete
  6. A Multi band tcvr project that was needed. Excellent work and management for bringing out such an innovative design.
    Wish you all the best.
    73's
    Sunil Lakhani
    VU3SUA

    ReplyDelete
  7. Very nice and economical setup. I would like to see more info PCB circuit ,etc. Good Ham radio!!
    Ahappy new year to all !
    Baruch 4z4rb

    ReplyDelete
  8. Well done Sailin. I once had a SSB chat on 40 meters with a chap in South Africa who had built a 2 watt rig from a design he found on a website in India. The motive behind the design was the same as yours - if you cant find a torroid, use some tap washers! the fact of the matter was that it worked and worked well.
    You have obviously overcome the adversity of not having readily available components and have come up with a workable rig.
    I salute you for the work you have done.
    73 de ZL2AIM Ian (previously ZS5IAN)

    ReplyDelete
  9. Sailin,

    Do you have a link to a complete set of schematics to the unit? I would like to try to replicate some of what you have done.

    73 de AD5TU

    ReplyDelete
  10. Do you have a complete set of Schematis available for this unit?
    I would like to build one for when I get back on the air, I am going after my ticket again after more than 40 years off the air now that I am retired and have time to do it.

    ReplyDelete
  11. Nice Rig, Congrats from OE

    55, 73 de OE2HEM

    ReplyDelete
  12. Thanks so much for making this rig available. I have been looking for something like this for years. Finally we may be able to home build one. VE6LRC
    73's

    ReplyDelete
  13. Sailin,

    This is a great piece of engineering work. I would like to see more on this design such as a schematic and PC Board artwork. This is something I also would like to build.

    73
    Mikw K1EG

    ReplyDelete
  14. Sailin,

    This is a great piece of engineering work. I would like to see more on this design such as a schematic and PC Board artwork. This is something I also would like to build.

    73
    Mike K1EG

    ReplyDelete
  15. Hi all friends,

    this is really excelent project but I didn't find the circuit of transceiver!!!!!

    ReplyDelete
  16. Circuit of transceiver:

    http://shipwreck.yi.org/documents/projects/homebrew/vu2hmy_2K8_All_band_SSB-CW_XCVR.pdf

    ReplyDelete
  17. correct link:

    http://shipwreck.yi.org/documents/projects/homebrew/vu2hmy_HMY2K8_All_Band_SSB-CW_XCVR.pdf

    ReplyDelete
  18. Excellent design from what I can see of the project and craftsmanship on the faceplate is real clean and simple. Any pics of your finished rig yet?

    73,
    Anthony
    KB3RJH

    ReplyDelete
  19. Hi Sai,

    I understand that PCB's are available from you for this project. Could you please advise on how to get these PCB's.

    73
    Mike K1EG

    ReplyDelete
  20. Real spirit of a ham is seen in this tx/rx design. This should be a milestone for future designers.

    ReplyDelete
  21. Hi its amazing, Can I have the PCB.. if its available pls send a note to vu3tmt@gmail.com. I will contact you personaly

    ReplyDelete
  22. great mineral makeupFebruary 26, 2009 at 1:40 AM

    This comment has been removed by a blog administrator.

    ReplyDelete
  23. Supereb Awesome work. I'll watch the firangs go green on this.

    ReplyDelete
  24. Excellent info dear friend.

    ReplyDelete
  25. Now that you have kindled the fire, you would be the one to douse it.It can only be doused by coming up on air with this rig on my table,.... homebrwed by me.send me the info not posthaste but e-mailhaste.i cant wait for long____. 73 vu3vkl

    ReplyDelete
  26. Without the Linear Amp PCB and the DDS Vfo the project seems incomplete

    ReplyDelete
  27. Excellent project Congratulations!!!!!!!!!!!!!!

    But you have not mentioned about the LSB and USB crystals. How these values could be found? I mean exact value can be hard to find.

    Javed Afridi

    ReplyDelete
  28. My E-mail address:

    -------@yahoo.com

    put mjafridi before @

    Javed Afridi

    ReplyDelete
  29. Well done job and great efforts, could you share the schematics and photos of your rig. More hints about parts sourcing (j land + other sources also)

    ReplyDelete
  30. If you are providing just the details of your rig, it becomes one of and anybody attempting it needs to start from scratch. Full info would help everybody as one need not hunt for it.

    ReplyDelete
  31. Dear sir,
    Greetings,
    Thank you very much for EyeBall QSO on 08.01.2011 and the seting HOmebrew TRX (Designed by the VU2DEV and the Rx which was homebrewed during the RX workshop in Trivendrum. I am alway thankful to you VU2HMY VU3AUZ and VU2DEV. Thankyou once again. and 73 VU2VIZ, Mohiddin Basha syed

    ReplyDelete
  32. muito bom seu projeto multibanda e facil de montar, eu tambem sou um construtor de qrp, so AM, não sabia como suprimir as bandas laterais para ter LSB e USB agora graças a voce posso fazer projetos com filtros de cristais em serie ate mesmo de 455Khz. muito obribado Waldir Cardoso Brasil.

    ReplyDelete
    Replies
    1. This comment has been removed by the author.

      Delete
  33. Dear sirs, greetings. I request that i may kindly be considered for such kit for my sack. Seasons greetings all the best wishes from mohiddin basha. VU2VIZ.

    ReplyDelete
  34. Could you help me?
    I didn't find the DDS schematics and .hex codes (PIC?).

    ReplyDelete
  35. Thank you VU2SGW for having introducing HMY2K8 multiband TRX of Dr Rajasekhar of Nellore of Andhra Pradeh. Seasons greetings and all the best wishes to you all.

    ReplyDelete
  36. very nice and i like the way you express everything. I hope every reader take advantage of this useful info..PCB

    ReplyDelete
  37. The circuit of TRX by HMY is a replica of Ararenah monoband TRX, modified with Band switching of the bands.
    The circuit is simple, straight and requires much winding and tuning of the coils.
    The greatest draw back is its PCB available with HMY. It is very congested, tracks are very close and chances of bridges are high. Components are vertically mounted and . Assembling the same is not user friendly. A few rupees more spent for the PCB to make it a bit larger would have made it easy for assembling.

    ReplyDelete
  38. Do you send PCB. mail details to vu3phn@yahoo.com

    ReplyDelete
  39. Dear VU2HMY,
    Thank You for taking effort in designing such a wonderful piece of equipment. I go by the call sign VU3JTH and the handle is Jacob. I am pursuing Btech in Mechanical Engineering. Was looking for a homebrew project that could help me make a versetile equipment other than the ordinary monoband rx and txrs; didnt find anything till i heard abt ur project from VU3AUZ who gave me the board. I am not much familiar with electronics or home brewing. Can you pls help me get the schematics on the circuit? the link http://shipwreck.yi.org/documents/projects/homebrew/vu2hmy_HMY2K8_All_Band_SSB-CW_XCVR.pdf i got from the comments above seems to be invalid. I'll be checking this page for the next few weeks for ur reply or if its ok with you my mail id is jac.thomas@live.com. Regards to you and your family

    ReplyDelete
  40. Thank you VU2SGW for having introducing HMY2K8 multiband TRX of Dr Rajasekhar of Nellore of Andhra Pradeh. Seasons greetings and all the best wishes to you all.
    Do you send PCB. mail details to nassfars@gmail.com
    Regards to you and your family

    ReplyDelete
  41. Hi everyone. i want to build this RF amp with IRF510 the Dr. R. RAJASEKHAR, VU2HMY circuit . but i don't have the PCB of this file please help me this is my email address hassandelghavi@gmail.com with thanks EP5HD

    ReplyDelete

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