CHEAP EFHW ANTENNA with AIR DIELECTRIC

( ENGLISH BEGIN after INDONESIAN )

Dari banyak referensi tentang EFHW antenna yang saya baca, paling banyak artikel yang membahas penggunaan toroid jenis Ferrite FT untuk matching transformernya, kemudian menggunakan toroid jenis Iron Powder, dan terakhir menggunakan inti atau dielektrik udara sebagai matching transformer.

Keunggulan penggunaan Ferrite Ft adalah “broadband” , tapi untuk Ferrite ukuran besar seperti FT240-43 sulit didapatkan di sini, jika beli online dari ebay, harganya bisa mencapai Rp 400’000 sd Rp 600’000 , itu terlalu mahal.

Pilihan berikut menggunakan toroid dari Iron Powder, yang umum dipakai warna merah, contohnya T200-2, harganya lebih murah, mungkin sekitar Rp200’000 sudah bisa diperoleh, sifat daripada toroid iron powder ini pada EFHW matching transformer disebut sebagai “monoband”.

Pilihan terakhir untuk matching transformer adalah menggunakan dielektrik udara, kenapa tidak ? Alasan pertama yang jelas adalah sangat MURAH, kelebihan lain bisa dibuat QRO, walaupun sifatnya “monoband”. jika diinginkan bekerja di band lain, cukup dengan membuat lagi radiator antena dan matching transformer yang baru, toh harganya murah sekali.

Percobaan sederhana dilakukan dengan transmit 100 Watt selama beberapa menit, membuktikan bahwa toroid matching transformer yang paling panas adalah dengan ferrite FT240-43, jika sudah panas SWR akan naik alias tidak match lagi.
Berikutnya untuk matching transformer dengan iron powder T200-2 toroid hanya sedikit hangat saja dan SWR tidak begitu terpengaruh, lebih effisien dari pada FT dan terakhir jika menggunakan matching transformer dengan dielektrik udara tidak ada masalah panas.

Secara umum, tipe matching transformer untuk EFHW dengan menerapkan induksi dari gulungan Primer ke gulungan Sekunder, antara gulungan Primer dan Sekunder ada yang sharing ground dan ada pula yang tidak, biasanya yang tidak sharing ground dimaksudkan untuk QRO, seperti gambar berikut :

Tapi tunggu dulu, ternyata masih ada tipe matching transformer selain di atas, yaitu menggunakan tap, tipe HPF ( high pass filter ) dan tipe LPF ( low pass filter ), jelasnya lihat gambar berikut :

Alasan penggunaan matching transformer tipe HPF jika dekat lokasi anda ada pemancar Broadcast yang mengganggu penerimaan, jika dibandingkan dengan tipe matching transformer sebelumnya, tipe LPF dan HPF ini coilnya lebih sederhana, tanpa tap dan tanpa gulungan sekunder, melulu hanya satu coil saja, ini merupakan keuntungan karena mempermudah pada waktu membuat coil.

Berikut ini adalah matching transformer EFHW yang saya buat, saya gunakan tipe LPF, untuk capacitornya saya gunakan beehive capacitor dengan kelebihan bisa dituning naik atau turun , alternatif lain menggunakan potongan kabel coaxial sebagai pengganti beehive capacitor, dengan konsekuensi tuning hanya bisa sekali jalan dengan cara memotong sedikit demi sedikit kabel coaxial sampai tercapai kondisi SWR terbaik pada frekuensi kerja yang diinginkan. Posisi coaxial sebagai capacitor bisa digulung di dalam box. Jangan lupa MUTLAK diberikan counterpoise atau ground untuk membantu mencapai yang SWR rendah.

Buat coil dengan nilai induktansi sedikit lebih besar daripada target, atau tambahkan saja sekitar 5 lilitan. Salah satu ujung coil dibuat semi permanent dengan selotape kertas, sambil dituning capacitornya, coil bisa dikurangi sedikit ( jangan diputus dulu, biarkan tergantung ) atau digulung balik sampai tercapai SWR terendah, jika sudah tercapai, kawat coil yang kelebihan bisa dipotong dan dirapikan permanen.

MY 7MHz QRP LPF EFHW MATCHING BOX

VERTICAL EFHW dengan DIELEKTRIK UDARA, MATCH di 7.05 MHz dan 4 MHz dengan SWR sekitar 1.4 – 1.5

CONTOH QRO LPF 20M

COAXIAL CAPACITOR, PADA UJUNG SERABUT DIKUPAS 1CM DARI UJUNG INNER

OUTSIDE PLUG ABLE COAXIAL TRIM CAPACITOR for EASY ACCESS

Pakai saja radiator multiband, sehingga hanya perlu mengganti matching transformer yang sesuai dengan band yang diinginkan tanpa harus mengganti radiator lagi.

Selamat berkarya, semoga bermanfaat, dengan bahan yang murah bisa didapatkan hasil yang memuaskan dan tidak kalah dengan penggunaan Ferrite atau Iron Powder toroid.

Referensi : AA5TB, M0UKD, PD7MAA, N4SPP

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ARDUINO ANALYZER

( ENGLISH begin after INDONESIAN )

Halo teman – teman, kali ini saya baru bikin sebuah alat baru, namanya ARDUINO ANALYZER. Alat ini sangat berguna sekali untuk menunjang kegiatan homebrewer, fungsinya antara lain : signal generator mulai AF sampai RF ( HF ), AF & RF detector untuk menganalisa respon frekuensi dari filter, antenna SWR analyser. Karena bisa menampilkan grafik untuk menunjukkan respon frekuensi filter atau respon SWR, tentunya secara visual lebih unggul daripada menggunakan indikator jarum atau angka. Untuk referensi sumbernya, silakan merujuk ke PY2OHH web site, artikel no. 152 ANALISADOR de RF com ARDUINO , semua petunjuk lengkap dan cara penggunaan ada di sana, artikel lain yang berkaitan dan wajib dibaca adalah no. 151 tentang modifikasi kaki DDS Modul AD9850 dan artikel no. 143 tentang cara mendeteksi kode tombol sembarang remote.

Cara menggunakan alat ini sangat mudah, ada sepasang port RF OUT dan RF IN, sepasang port AF OUT dan AF IN, port ANTENNA untuk mengukur SWR, dan yang menarik untuk kontrol menu nya bisa menggunakan sembarang remote TV, saya berpendapat lebih intuitif dan awet dari pada menggunakan rotary encoder.

Sepintas jika kita lihat skemanya cukup besar, tetapi jika diperiksa lebih lanjut skema ini terdiri dari bagian – bagian blok yang sederhana yang digabungkan jadi satu skema yang besar. Hal ini membuat saya memberanikan diri melangkah lebih lanjut. Seperti biasa agar rapi, saya buat gambar rencana kerja per blok, ada 2 pertimbangan, menggunakan pcb lubang – lubang atau merancang jalur pcb, karena kebetulan pada saat ini saya sedang belajar menggunakan software EAGLE. Saya paling malas jika harus mengebor lubang kaki komponen pada pcb karena tidak punya alat bor statis. Jika memakai bor tangan hasilnya tentu kurang rapi. Ada pilihan mode SMD pada EAGLE, saya pakai ide ini, dengan membuat sendiri library komponen through hole tapi dengan kaki model SMD, dengan tujuan tidak perlu mengebor pcb. Pcb model ini dikenal dengan nama muppet pcb.

Total diperlukan 3 lembar pcb dengan ukuran sekitar 9×8 cm. Khusus untuk 1 pcb terpaksa memakai mode through hole dan mengebor, karena isinya adalah Arduino Nano dan DDS module AD9850.

Pada blok antenna analyser, rangkaian yang saya buat tidak bekerja sebagai mana mestinya, ketahuan dari serial monitor bahwa port A4 dan A5 tidak mengeluarkan output tegangan yang benar, setelah saya modifikasi, IC TL082 di by pass, atau output tegangan forward dan reverse dari jembatan Wheatstone langsung dihubungkan ke port A4 dan A5, dan sumber RF signal ke jembatan Wheatstone diambil dari output RF Amplifier, lantas rangkaian ini dapat bekerja dengan baik.

Berikut ini adalah modifikasi dari skema asli sbb :

MODIFIED SCHEMATIC of ARDUINO ANALYZER – PY2OHH Copyright

Contoh penggunaan alat ini antara lain :

CRYSTAL FREQUENCY SORTING, THE RED LINE IS FREQUENCY MARKER

MY VERTICAL 40m EFHW SWR

MY BITX Spectra XTAL BANDWIDTH, RED LINE is CARRIER FREQUENCY

Pada artikel no. 152 ada terlampir 2 sketch arduino, pakai yang bawah setelah list material.

Jika tersedia remote selain TV SONY , kode tombol remote tsb. harus dideteksi dulu dan dicatat kodenya untuk masing – masing tombol, setelah itu kode bisa disalin ke sketch, sekali lagi lihat artikel no. 143 pada web site PY2OHH.

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ARDUINO ANALYZER

Hello friends, I have just made a new tool, called ARDUINO ANALYZER. This is very usefull tool for my homebrewing works, some functions are : AF to RF ( HF ) signal generator, AF and RF detector to check filter response frequency, and SWR antenna analyzer. Since its show graphic respons of SWR or filter, visually better than needle or number display.
The original page is from PY2OHH web site, see article no. 152 ANALISADOR de RF com ARDUINO , the complete instruction and how to use this tool are there, the related article and must read are no. 151 about DDS module AD9850 pin modification and article no. 143 about how to detect any TV infra red remote control .

Operations is easy, there are couple port of RF OUT and RF IN, also AF OUT and AF IN, and ANTENNA port for SWR measurement, the interesting way is use any TV remote control to access menu, looks more intuitive and more durable than rotary encoder.

My first impression, the schematic is quite big dan complicated, further study and separate it into blocks make it more easier to understand. This make me sure that I could manage it. Considering between perforated pcb or design my own pcb. This time I was learning EAGLE software. I hate drilling pcb since I only have a hand drill instead of desktop drill. There is a SMD pcb mode on EAGLE, I use this idea for through hole component but with SMD pad, then no need to drill the pcb. I have seen this kind so called muppet pcb.

Needs 3 pieces sandwiches pcb, each about 9×8 cm. I have to drill use through hole for one pcb that contained Arduino nano and DDS module AD9850.

The SWR antenna analyzer section did not works, I knew it when I check the A4 and A5 output, via serial monitor, the output voltage was not correct, after try some modification, by passed IC TL082, or direct the forward and reverse output from the Wheatstone bridge to A4 and A5 port, also the signal source to the Wheatstone bridge is feed from the output of RF amplifier, then the circuit could perform well.

Below is the modified schematic :

MODIFIED SCHEMATIC of ARDUINO ANALYZER – PY2OHH Copyright

Some pictures :

CRYSTAL FREQUENCY SORTING, THE RED LINE IS FREQUENCY MARKER

MY VERTICAL 40m EFHW SWR

MY BITX Spectra XTAL BANDWIDTH, RED LINE is CARRIER FREQUENCY

There are 2 arduino skecth at article no. 152, I use the one after material list.

If you have any TV IR remote others than Sony TV, the remote key code must be detected first, then copy the code to the sketch, again please see article no. 143 at PY2OHH site.

Degen321 Pocket SW RX Modifications

FREQUENCY COUNTER

How much does the price of a frequency counter? How about making my own? Well it’s quite expensive, and if you want to create your own, you can not guarantee the precision anyway, such an answer from a friend when he asked about the frequency counter.

Realized the need for this tools is necessary, especially if we play the radio frequency electronics. After collecting references from various sources on the internet, with keyword “homebrew frequency counter”, I chose a project that feels pretty easy , with common components and minimum, and decided to make it.

It’s a SIMPLE FREQUENCY COUNTER WITH 8 LEDS DISPLAY from PA2OHH site.

SIMPLE COUNTER

INSIDE SIMPLE COUNTER

What can you do with this frequency counter?  Of course measure  frequency output of your oscillator, but further you can compare between what is calculated or designed on paper with the one you measured. If you have a known precision capacitor or known precision inductor use them alternatively in your oscillator as a tool for measuring unknown L or C value, so you now have a LC meter here.

Use formula  LC=25330/F^2, where units are uH, pF and MHz

However it is very funny to see the LED alternatively on off while moving the frequency dial.

Back to my friend opinion, do we really need to buy such a precision counter ? No, since we are amateurs, it’s well worthy to make yourself, even this simple counter means a lot, at least you know where you are when you working on your frequency.

ANOTHER HOMEBREW DECIMAL COUNTER

Here is another homebrew counter I have made, A DECIMAL COUNTER also from PA2OHH, this is better from previous counter since frequency reading is more easier.

Note how to read the counter, at 19.8 MHz or 29.8 MHz ( missed type 20.8 MHz ), reading is 9.8 MHz.

DECIMAL COUNTER

HOW TO READ DEC COUNTER

INSIDE DEC COUNTER

ANOTHER HOMEBREW ONE SEGMENT COUNTER

Also from PA2OHH site, there are various frequency reading you can choose : a one 7 segment LED, a buzzer for morse code and a RS232 for connection to PC via software.

This counter using Atmel AT90s-1200 as a microcontroller.

ONE 7 SEGMENT COUNTER

INSIDE ONE 7 SEGMENT COUNTER

REGEN RADIO

This is the first project that I worked after long time absent playing electronics.

I remember when I was at Junior High School, at that time  the source of learning electronics was quite limited here, no internet, just some excerpt article clipping or photo copy from borrowed electronic magazine. But things has been changed, I gathered and understand so much information from various electronics web site. See Ian Purdi – electronics tutorials web site, I am start learning from here, understand such thing named coil or inductor, this coil related thing probably nightmare among us, for example given a schematic, the coil specification was : J. W. Miller 112-H6, or toroid T50-6…. ?? What is this thing ? Where to buy it ? Can I make it ? No one sell it here, I ask a service man, maybe he know something from his experiences, he also did not have an idea and could not give answer that I needed. So mostly the schematic journey was ended here.

My enthusiast passion was at radio frequency project such as walkie talkie, SW radio etc.. Some friend have so much progress than me, but he was into hi-fi amplifier things that I am not interested.

I just feel that radio ( receiver ) thing is amazing, a magic thing !

Back to Ian Purdi’s tutorial, there are lessons about oscillator, he teach how to calculate and constructs such coil, calculate the working frequency  etc. These are the lessons that I want so long !

He also have a nice project to build : Regenerative Radio a la Kitchin. Wow , now reading this schematic is very enjoyment, I could understand even could design my coil for desired working frequency, I recommended this project for: easy to build ( relative ), not so much components, clear explanations and instructions, cheap and the result could be very nice. You will have enthusiasm and confidence to the next projects. And at last getting new experience with art of unusual tuning.

Components are not critical, any available FET can be used, just give attention to coil construction :

1. Note how to wind,  L1, L2 & L3 all must be in same direction. Case of error found in a friend, one coil in in other direction.

2. Another case at L3, coil winding is not enough, for example it mentioned 3 reels, but only 2.5 reels coiled, so the regeneration does not occur or too weak, if necessary make experiment by first adding 1 to 2 reels at L3,  and see how is the result.

3. Space between L1, L2 and L3 according to some article are spaced about 3 mm, but according to my own experiments, space is closed.

4. L3 position is lowest, space between L3 to ground plane pcb not to closed, try at least 2 cm.

This is the first time I try assembling methods so called “Manhattan Island”, where a small piece of pcb glued with super glue to mother board ground plane pcb. Nowadays I preferred “Rat Nest” or “Ugly Construction” assembling method, this is much faster but at some point still use Manhattan Island as a pad, but I do not use super glue any more, I used a double ( adhesive ) tape, very quick. This kind of tape have a black sponge with green insulation, I see glazier used to attach the mirror to the plywood, with time, it become stick very strong. If exposed to soldering heat, let it sit until cool, he will stick again. Scissors the double-sided tape  into small pieces, according to the size of the pcb pad that will be attached.

MODIFICATION:

– Adding FINE REGEN using diode or LED as a varactor, in my opinion is absolute to be added, this addition make regen setting much smoother, much easier.

– Capacitor C3c with value 5 pF is good enough for fine tuning in AM mode, but for SSB mode this is somewhat oversized, replace with 1~2 pF.

– Potensiometer for a long time tend to become dirty and make a noise ” crack – crack” could be replaced the VOLUME potensiometer with fixed resistor with SELECTOR SWITCH , while for ATTENUATOR potensiometer could be replaced by plastic varco, see schematic of AA5TB.

– One thing that has not been satisfying me, is the sound output of the LM386 is too small, I try to add a preamp, the results are not in line with expectations, resulting in the motor boating, and sound output also not increased significantly, please advise from readers. The AF amplifier experiment ended with TBA810, still too weak.

Fortunately I have built my guitar amplifier using LM 1875  ( see my amplifier at http://amplifier-guitar.blogspot.com/), plus a FET preamp.  I can use this with my regen, sound is so powerfull, remembering me to the voice of my grandpa’s Philips old valve radio.

Recently I read an article at QRP-SWL Homebuilder web site ( this is one of the very good site ) about LM1875 and e-mail to owner site Todd VE7BPO. I asked him a suggestion for a preamp that suit for this configuration ( homebrew rx + pre-amp + LM1875 ). A homebrew rx could be : kitchin regen, PA2OHH shortwave rx, PY20HH DSB TRX etc.

Not too long, he replied my letter explain that he make and tweak a pre-amp for me ( thanks ! ) :

Hi Indra:

I liked your blog.
Based on some work by Douglas Self; a prodigious Audiophile EE/author — This is the best “popcorn” AF pre-amp I’ve built — in that with a load R of ~1K or greater the output stays clean until above 7.04v peak-peak with only ~ 5 mA of current . Low distortion at .002%. The boot-strapping boosts Q1 gain and the current source on the emitter follower extends the ability of this amp to drive even smaller load impedances quite well.

This should boost up your signal nicely. The 1K input resistor called “R” can be increased or decreased. The minimum would be 100 ohms as to prevent oscillations. If your input signal is too large and gets distorted, increase R to between 1K5 to 4K7.

The output 1K resistor can be your volume control pot or any load greater than ~ 1K

I know it looks a little “busy” but this amp is staple, very clean and can swing a large AC signal

Cheers
Todd

MINI REGEN a la ONNO (PA2OHH)

This is another regenerative radio from Onno ( PA2OHH ).

The results were not too good, noissy compared with Kitchin regen. There is interference from FM broadcasts, but this can be overcome by adding a 10 pF capacitor in transistor T1. But I like it smal size.

DDS VFO using MICROCONTROLLER

( ENGLISH begin after INDONESIAN )

Saat pertama kali membaca artikel ini di web site PA2OHH, saya tidak mengerti apa itu DDS VFO. Setelah membaca dan mempelajari lebih lanjut ini pada dasarnya adalah sebuah LC-VFO, tapi dikontrol oleh sebuah microcontroller, tentunya menjadi sangat stabil karena ada mekanisme penguncian frekuensi, selain itu juga ada display frekuensi minimalis.

Selanjutnya saya memeriksa apakah komponen – komponennya tersedia di pasaran atau tidak, khususnya:
10mH coil, varactor BB212, uC AT90S1200.

AT90S1200 tersedia, coil 10mH tidak ada di pasaran, untungnya teman saya pernah memberikan sebuah toroid ( merk KDK ) bekas switching power supply, yang mana setelah diukur dengan LC meter lilitannya dapat mencapai nilai 10mH, masih kurang 1 toroid lagi, ternyata ada toko yang menjualnya.

Tidak ada varactor BB212 di pasaran, saya hanya punya varactor bekas TV tuner dan beberapa MV209, kapasitas maksimum hanya 30pF, OK saya kira mereka bisa diparalel nantinya.

Saya sama sekali belum punya pengalaman dengan microcontroller, saya tanyakan bagaimana caranya ke PA2OHH, dan dijawab beliau dengan postingan artikel baru yaitu : HOW TO PROGRAM THE AT90S1200 MICROCONTROLLER. 

Agar rapi, pertama saya membuat gambar kerja penataan komponen, satu persatu komponen disusun sesuai skema. Setelah gambar komponen tersusun per tingkat, berikutnya baru merakit komponen per tingkat pada pcb, setelah semua tingkatan tersusun pada pcb, baru dihubungkan dengan kabel antar tingkat tersebut. Semua dikerjakan dengan metoda Ugly Construction.

Setelah semua komponen terpasang rapi pada pcb, waktunya untuk memprogram UC, seingat saya, kecepatan WRITE diset paling lambat, karena untuk menyesuaikan kecepatan komputer cukup tinggi. Saat ini alat UC programmer dan softwarenya hilang, sehingga untuk tidak dapat memberikan informasi lebih detail tentang hal ini.

Ada modifikasi pada VFO dari skema aslinya, karena kapasitas maksimal varactor yang tersedia hanya 30pF, butuh diparalel hingga 4 varactor, dan diseri dengan capacitor 1nF ( nilai komponen dari coba – coba ).

Untuk coil, agar menghemat tempat digulung pada karet berbentuk donat, buat sembarang 1 coil dulu, ukur dan catat nilai induktansinya dengan LC meter, pasang, monitor dan catat batas / range output frekuensinya.
Lantas buat coil berikutnya, induktansinya harus sambung dengan frekuensi yang dihasilkan sebelumnya, tentu diperlukan sedikit overlap frekuensi. Demikian seterusnya sehingga mendapatkan lebar frekuensi yang diinginkan, dalam hal ini HF.

Untuk mengatasi kelangkaan varactor, ini ada beberapa ide, tapi belum pernah saya coba, sbb : pakai sembarang varactor dengan nilai seadanya, bisa memakai LED, 1N4007, mungkin dengan disusun katoda ketemu katoda. Lantas diparalel dengan Varco plastik ~300pF, Varco ini berfungsi sebagai penalaan cepat, baiknya ditambahkan roda Varco agar lebih halus.

 

Saat pertama kali dinyalakan, rangkaian tidak bekerja, setelah pusing 2 minggu mencari kesalahan, ketemu ada kesalahan pada skema, pin 10 (GND) dari UC, tidak disambung ke ground, begitu disambung, rangkaian langsung bekerja dengan baik. Skema saat ini sudah dikoreksi oleh PA2OHH.

Cara termudah untuk uji coba DDS ini adalah menggunakan sembarang radio shortwave, tepatkan frekuensi DDS di sekitar frekuensi radio SW, akan terdengar zero beat yang kuat, perlahan lahan naik/turunkan frekuensi DDS, sambil menaik/turunkan frekuensi pada radio SW, dengan cara ini sampai mencapai batas atas/bawah dari coil yang bersangkutan, dan catat frekuensi tersebut.

Lantas buat coil berikutnya, dst.

Output power dari DDS ini cukup datar, sekitar +15dBm ( 30mW ), di atas 20MHz sedikit menurun, pada 29MHz output power turun hingga +3dBm ( 10mW ), output power mencukupi untuk disuntikkan ke diode ring mixer. Pengukuran dilakukan dengan 50 Ohm diode Wattmeter terkalibrasi.

Untuk saklar selector, baiknya menggunakan yang berkualitas baik, terbuat dari plastik warna biru putih, mekanisnya terbungkus di dalam, kliknya halus dan ringan, harga sekitar Rp25’000 di toko ELTECH – Pasar Genteng Surabaya. saya sudah terlanjur menggunakan saklar selector coklat, kadang – kadang kontak saklar kurang baik.

DDS VVO ini sudah saya coba dengan  SIMPLE PC RECEIVER WITH THE MICROCONTROLLER DDS dengan hasil yang sangat memuaskan.

Jika menginginkan DDS menampilkan batas frekuensi tertentu saja, PA2OHH memberikan caranya dari email beliau sbb :

How to change the display setings works as follows. In the software the .ASM file, readable in ASCII, there are 2 lines, one for minimum frequency of 1 MHz and one for the maximum of 39 MHz. This last one is a test for the value 57 as 57 = 3×16+9…….

Untuk QRP, ide display frekuensi minimalis dengan 1 led seven segment ini sangat bagus, tapi saya lebih suka LCD display untuk pembacaan frekuensi.

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First time read an article from PA2OHH’s web site about DDS VFO , I was curious, what is this thing called DDS VFO. Further reading  tells that this is basically a LC – VFO but is controlled by a microcontroller, indeed it is very stable because there is a locking frequency mechanism, also it has a minimalis frequency display.

Next step is to check whether the components are available in the market here or not, especially:
10mH coil, varactor BB212, uC AT90S1200.

AT90S1200 is available, I can not find 10mH coil in the market, fortunately I have a friend who gave me a toroid ( marked KDK ) from switching power supply, then as measured by LC meters can meet the 10mH, I only have one toroid, I seek the same toroid and it could be found on the market.

No BB212 varactor available in the market, I have some varactor from TV tuner and some MV209 maximum capacity only 30 pF, ok I think these could be paralleled.

Because I never have any experience with microcontrollers before, I asked to PA2OHH how, and he responded by posting the article about HOW TO PROGRAM THE AT90S1200 MICROCONTROLLER. .

For implementation to be neat, I prepare on shop drawings first, sketching from schematic part by part . After finished drawings of each part, then I arranged the components ( by part ) in pcb, if all the parts are finished, then connect each part with connecting cable. All done in ugly construction method.

Once all components are neatly mounted on pcb, it’s time to program the UC, as I remember, the WRITE speed to be set at slowest, because the computer speed is quite high. Currently, I lost my UC programmers and software tools, so I can not give more details on this.

There is a modification in my VFO, since my varactor maximum capacity only 30 pf, I have to parallel four varactor, then series it with a 1 nF capacitor ( value from experiment ).

For the coil, to save space I wound it on a rubber donut-shaped, first make just one coil, measure it with LC meter and record the value, monitor and note the output frequency. Then make the next coil,  inductance must meet to follow the frequency generated previously, of course with a little frequency overlapping. And so on until completed a frequency range that we want, in this case the HF.

To overcome the unavailability of varactor, currently there are some ideas, but I’ve never tried, as follows: use varactor for locking mechanism with a small capacity, can use LEDs, or 1N4007 diode, may be mounted back to back. Then parallel these with plastic Varco with big capacity ~ 300 pF, this Varco served as a coarse tuning, I think we need to add Varco wheels to be more smooth.

 

INSIDE DDS LAYOUT

 

INSIDE DDS 1

The first time switch on, the circuit does not work, after 2 weeks of dizziness search, found there was an error on schematic, at pin number 10 of UC, the scheme is not reflected connect to the ground, once connected, the circuit works fine. The scheme has now been updated by PA2OHH.

The easiest way to test this DDS is to use a shortwave radio, sweep DDS frequency around the tuning frequency SW radio, you will hear strong zero beat, and very slowly sweep up (or down) the DDS, while tuning up ( or down ) the SW radio, this way until you reach upper ( or lower ) frequency range of coresponding coil is known and noted on paper.

Then make the next coil, and so on.

The DDS power output is quite flat, about + 15 dBm ( 30 mW ), above 20 MHz start slighty down, up to 29 MHz output power down to +3 dBm ( 10 mW ) , power output level is adequate to be injected into diode ring mixer. Measurement done with simple calibrated Wattmeter at 50 Ohm environment.

Better use a good quality selector switch, the body is from white & blue plastic, mechanism is wrapped inside, “click” is smooth not heavy, price about US$ 2.5 at ELTECH store – Pasar-Genteng-Surabaya. I already use ordinary brown selector switch, sometime switch behaviour does not connected correctly.

I have tried this DDS VFO with PA2OHH’s  SIMPLE PC RECEIVER WITH THE MICROCONTROLLER DDS with satisfaction result.

If you want to display certain frequency range , PA2OHH mention in his email as follows:

How to change the display setings works as follows. In the software the .ASM file, readable in ASCII, there are 2 lines, one for minimum frequency of 1 MHz and one for the maximum of 39 MHz. This last one is a test for the value 57 as 57 = 3×16+9…….

The minimalis frequency display is very good QRP idea indeed, but I prefer LCD display for frequency counter.