Renaissance of HF DC (Direct Conver

Renaissance of HF DC (Direct Conversion) receivers
Part1


Dipl ing. Tasić Siniša-Tasa YU1LM/QRP




First receiver I was ever built for HF was tube receiver without RF amplification called OV2 .It was working good and enable me to listen short waves and HAM bands. After that I build super heterodyne receivers but when I built DC transceiver by W7EL at the beginning of 80’s ZL2BKW version I was surprised how good DC receiver can be. With simple dipole antenna for 7MHz I worked 102 DXCC in 1985/86 with not to often work and with output power 1W (BD135 output transistor). After that I made a lot of HF and VHF DC receivers HAM and for professional use, my or other authors design. In year 2000 I made presentation in KKE club Belgrade with next subject “Renaissance of HF DC receivers”. Paper material contains 30 pages collected materials about DC receivers with schematics, useful formulas for calculation, PCBs and complete receivers made or design by author. I received in last time over 40 request for the translation original article. This is translation of original article from year 2000. Now in 2007 I have quite different point of view to the some subject and because of that I am preparing new article part 2 with direct receivers designed and tested by author. I apologize that this materials schematics and comments on them are still written on Serbian language Subject DC (direct conversion) receivers in next text DC is not often subject in amateur and professional articles and we can hard find some original designs and realizations. The older homebrew can remembered with an nostalgia DC receivers called OV1, .. or similar types .In late 60th, 70th this was the easiest way to receive HF broadcast and amateur bands. These types of receivers have relative good sensitivity. Super-regenerative process is used for the demodulation SSB/CW signals. The situation on HF bands now is quite different that it was at that time. HF bands are now crowded with enormous big number strong signals. The DR (dynamic range ) this kind of receivers is very poor and receivers are producing a lot of IMD and non existing signals in the air. Because of that this kind of receivers which still have big use specially in simple alarm, remote control receivers I will not take in consideration. In this article I shall describe receivers with next block diagram pic1. These receivers have separated LO (local oscillator called VFO or BFO) and they can be divided in 3 main categories:

1. DC receivers without image rejection

2. DC receivers with image rejection

3. DC receivers with image rejection according to the third method called DC RX Weaver type.






Pic1. DC RX block diagram

Before we start with DC subject I shall make short comparison between DC (direct conversion) and super-heterodyne RX-s.

The super-heterodyne receivers are:
-complicate with their block diagram structure and extremely complicate for adjustment. Generally they are very expensive (
big number different IF filters, mixers…etc)
-they have problems with image frequency (Fin+/- IF), with IF(intermediate frequency) choice and with choice mixing plan.
-they have problems with frequency synthesis (multiple PLL loops and phase noise).
- The main problems in super-heterodyne RX homebrew are related to the RF problems, but not only to them.
- The biggest advantage of this kind of receiver is that with careful design and proper component choice we can obtain very good performances. This results aren’t accessible for the most homebrew amateurs reasons are components accessibility, their price, instruments for measuring and RF and other different kind of experience in receiver design area such as (DSP, computer)

DC receivers are from the other side:

-generally speaking substantially they are cheaper and simpler. This statement is true especially for the DC receiver in categorization number 1.
-they haven’t problems with mixing, phase noise as super-heterodyne receivers have.
-very big image rejection is hard achieve as it is possible with super-heterodyne receivers with IF filters.
-DC receivers are very sensitive to the strong broadcast AM (amplitude modulation) signals. In the case of DC receiver for 7
MHz we can hear unwanted music in the background which is hard to eliminate.
-high performances DC receiver isn’t simple and cheap. It is very hard design good DC receiver for several HF bands.
-the biggest DC receiver advantage for homebrew is that they need modesty RF experience and ordinary instruments like
DMM (better digital multi-meter, perhaps RF generator or oscilloscope) are.
- My personally experience and not only mine in DC receiver listening is that they are real HI-FI (high fidelity) music compared to the most commercial super-heterodyne RX-s.
In order to find better understanding DC subject modulation and demodulation process and reason for the phase shifting I
draw picture pic2. At the pic2 is done vector, oscilloscope and spectrum analyzer screen shoots for modulations such as AM/CW/SSB/DSB and way for the modulation and demodulation process. This pictures not take care complicate mathematical explanation of Hilbert transformations with positive and negative frequencies which is hard understandable for the most people even for the people which have telecommunication as professional job.

My initial idea for this article was to offer homebrew builders different solution separate functional blocks which will enable experimenting in the DC receiver field with different design solutions. This experimenting way enable testing and checking advantage and disadvantages starting from components which every individual homebrew have. Experimenting with different solutions will enable homebrew to have experience to make some new DC receiver or even transceiver for CW/SSB. I have to apologize for mistakes and inconvenience for them for all who start with my schematics. Author had tested the most of schematics but not all. Analyzes done in different CAD-s show that some authors wilfully and non wilfully gave wrong components values or that they are error during printing process. I tried to correct all error which I find. The design and realization LO (VFO or BFO) author didn’t consider in this article. Also input band pass BP filters aren’t taken in consideration and I proposed some relative simple and easy solution for practical BP realization.
DC receivers as I told at the beginning are simple constructions but they have some problems in design and realization about which we have to take care. This was very exactly counted and explained by N.Hamilton G4TXG in magazine Radio Communication 4/1991:
RF hum phenomenon, AC from power supply with 50 HZ is modulating LO (local oscillator). The side band component from 50 Hz we are hearing as hum. The 50Hz is retransmitting from power supply lines and than receiving with
RX antenna. This problem was described in ARRL handbook exactly. The solution for this problem is to screen LO or BFO in
closed box. The simplest solution is box from soldered PCBs peaces which is the easiest way for preparing and soldering.
The AM detection, phenomenon which I told that is typical for DC receivers. This phenomenon is happening in mixers because of their insufficient mixers (detector) linearity that they are working as AM detector. Demodulated signal is
than amplify by AF part of DC receiver. This phenomenon is happening also in super-heterodyne receivers but it is easy
eliminate with IF crystal filter. This phenomenon leads to solution with sufficient selectivity in front of mixer (demodulator). The selectivity will decrease numbers and power of unwanted, out-band signals. Switching mixers like 74HC4066,
74CBT3253 … will also decrease AM demodulations sensitivity substantially. Digital mixers enable us that we can directly
connect antenna to the mixer input without inputs filters. Imagine this test with any other mixer types like DBM (diode mixers). Mixer’s performance AM sensitivity is describing with signal in mV at mixer input which will produce unwanted signal at noise level (MDS).Good values for mixers are 5-10mV or signals S9 plus 50-60 dB at mixer input. Solution for this problem is utility of better linearity mixer. The diode mixers with anti-parallel diodes which have LO at 1/2 fs and they have the best AM rejection performances from the all diode mixers but I didn’t consider this mixer type reason is other their unwanted performances.

The AF hum effect is that AC 50 Hz directly in at AF part of DC receiver. Gain distribution is quite different for the DC receivers than it is for super-heterodyne receivers. 100 dB of AF gain is quite normal situation for the DC receiver realization. The solution for this situation is RX PCB screening and utility of coax cables for connections.
The microphonic effect is AF or RF origin. The AF microphonic effect can be solved with good mechanical RX construction with rubber spacers. RF microphonic effect is cased by leakage LO to the mixer (demodulator) input. The signal is then reflecting from input BP, mechanical change or mechanical shock are changing phase reflected signals. The result is AF signal or DC signal which is unbalancing mixer. The solution for this effect is utility high quality built in components, or use moulded coils especially in the diplexer, filter circuit.































































-AF loops and oscillations. This effect is happening especially when AF output amplifier drive speaker. The big gain in DC receiver, gain which is necessary for practical use, will cause voltage change in the lower signal stages and their detection. If we have bad parts or PCB circuits placement unwanted signals as parasitic modulations are amplifying to the clipping levels. The output signal is unpleasant for any listening. The solution for this phenomenon is to strictly obey rules for

good AF design with star ground configuration

Hasil (Bahasa Indonesia) 1:

Renaissance HF DC (Direct konversi) receiverPart1Dipl ing. Tasić Siniša-Tasa YU1LM/QRPFirst receiver I was ever built for HF was tube receiver without RF amplification called OV2 .It was working good and enable me to listen short waves and HAM bands. After that I build super heterodyne receivers but when I built DC transceiver by W7EL at the beginning of 80’s ZL2BKW version I was surprised how good DC receiver can be. With simple dipole antenna for 7MHz I worked 102 DXCC in 1985/86 with not to often work and with output power 1W (BD135 output transistor). After that I made a lot of HF and VHF DC receivers HAM and for professional use, my or other authors design. In year 2000 I made presentation in KKE club Belgrade with next subject “Renaissance of HF DC receivers”. Paper material contains 30 pages collected materials about DC receivers with schematics, useful formulas for calculation, PCBs and complete receivers made or design by author. I received in last time over 40 request for the translation original article. This is translation of original article from year 2000. Now in 2007 I have quite different point of view to the some subject and because of that I am preparing new article part 2 with direct receivers designed and tested by author. I apologize that this materials schematics and comments on them are still written on Serbian language Subject DC (direct conversion) receivers in next text DC is not often subject in amateur and professional articles and we can hard find some original designs and realizations. The older homebrew can remembered with an nostalgia DC receivers called OV1, .. or similar types .In late 60th, 70th this was the easiest way to receive HF broadcast and amateur bands. These types of receivers have relative good sensitivity. Super-regenerative process is used for the demodulation SSB/CW signals. The situation on HF bands now is quite different that it was at that time. HF bands are now crowded with enormous big number strong signals. The DR (dynamic range ) this kind of receivers is very poor and receivers are producing a lot of IMD and non existing signals in the air. Because of that this kind of receivers which still have big use specially in simple alarm, remote control receivers I will not take in consideration. In this article I shall describe receivers with next block diagram pic1. These receivers have separated LO (local oscillator called VFO or BFO) and they can be divided in 3 main categories:1. DC receiver tanpa gambar penolakan2. DC receiver dengan gambar penolakan3. DC receiver dengan gambar penolakan menurut cara yang ketiga disebut jenis DC RX Weaver. Pic1. Diagram blok DC RXSebelum kita mulai dengan DC subjek aku akan membuat pendek perbandingan antara DC (konversi langsung) dan RX-s Super-heterodyne.Penerima Super-heterodyne adalah:-rumit dengan struktur diagram blok mereka dan sangat rumit untuk penyesuaian. Umumnya mereka adalah sangat mahal (besar nomor berbeda jika filter, mixer... dll)-mereka memiliki masalah dengan gambar frekuensi (Fin +/-jika), dengan pilihan (frekuensi menengah) jika dan pilihan pencampuran rencana.-mereka memiliki masalah dengan frekuensi sintesis (beberapa PLL loop dan tahap kebisingan).-Masalah utama di Super-heterodyne RX homebrew yang terkait masalah RF, tetapi tidak hanya untuk mereka.-Keuntungan terbesar dari jenis penerima adalah bahwa desain hati-hati dan tepat komponen pilihan kita bisa mendapatkan kinerja yang sangat baik. Hasil ini tidak dapat diakses untuk yang paling homebrew amatir alasan komponen aksesibilitas, mereka harga, instrumen untuk mengukur dan RF dan lain berbeda jenis pengalaman di daerah Penerima desain seperti (DSP, komputer)DC Receiver adalah dari sisi lain: -umumnya substansial mereka murah dan sederhana. Pernyataan ini benar khususnya untuk penerima DC di kategorisasi nomor 1.-mereka tidak masalah dengan mencampur, tahap kebisingan seperti Super-heterodyne Penerima.-sangat besar gambar penolakan sulit mencapai sebagai mungkin dengan super-heterodyne penerima dengan jika filter.-DC receiver sangat sensitif terhadap sinyal siaran AM (amplitudo modulasi) yang kuat. Dalam kasus DC penerima untuk 7MHz kita dapat mendengar musik yang tidak diinginkan yang sulit untuk menghilangkan.-kinerja tinggi DC Penerima tidak sederhana dan murah. Hal ini sangat sulit desain baik DC penerima untuk beberapa band HF.-DC penerima keuntungan terbesar untuk homebrew adalah bahwa mereka membutuhkan pengalaman kesopanan RF dan seperti biasa instrumenAdalah DMM (lebih baik digital multi meter, mungkin RF generator atau osiloskop).-Saya secara pribadi mengalami dan tidak hanya saya di DC receiver mendengarkan adalah bahwa mereka adalah nyata musik HI-FI (kesetiaan tinggi) dibandingkan kebanyakan komersial Super-heterodyne RX-s.Untuk menemukan pemahaman DC subjek modulasi dan demodulation proses dan alasan untuk tahap pergeseran sayaMenggambar Gambar pic2. Di pic2 dilakukan cara untuk proses modulasi dan demodulation dan vektor, osiloskop dan spektrum analyzer layar tunas untuk modulasi seperti AM/CW/SSB/DSB. Gambar ini tidak mengambil perawatan rumit matematika penjelasan Hilbert transformasi dengan frekuensi positif dan negatif yang sulit dimengerti untuk kebanyakan orang bahkan bagi orang-orang yang memiliki telekomunikasi sebagai pekerjaan profesional.Ide awal saya untuk artikel ini adalah untuk menawarkan homebrew pembangun blok fungsional terpisah berbeda solusi yang akan memungkinkan bereksperimen di bidang receiver DC dengan desain berbeda solusi. Cara melakukan percobaan ini memungkinkan pengujian dan pemeriksaan keuntungan dan kerugian yang mulai dari komponen yang homebrew setiap individu memiliki. Bereksperimen dengan berbagai solusi akan memungkinkan homebrew untuk memiliki pengalaman untuk membuat beberapa baru receiver DC atau bahkan transceiver untuk CW SSB. Aku harus minta maaf atas kesalahan dan ketidaknyamanan bagi mereka untuk semua orang yang mulai dengan skema saya. Penulis telah diuji sebagian besar skema tetapi tidak semua. Menganalisa dilakukan dalam CAD-s acara yang berbeda bahwa beberapa penulis sengaja dan bebas sengaja memberikan nilai-nilai komponen salah atau bahwa mereka adalah kesalahan selama proses pencetakan. Aku mencoba untuk memperbaiki semua kesalahan yang saya temukan. Merancang dan merealisasikan penulis LO (VFO atau BFO) tidak mempertimbangkan dalam artikel ini. Juga masukan band pass filter BP tidak diambil dalam pertimbangan dan saya mengusulkan beberapa solusi relatif sederhana dan mudah untuk praktis BP realisasi.DC receiver seperti yang saya bilang di awal konstruksi sederhana tetapi mereka memiliki beberapa masalah dalam desain dan kesadaran tentang apa yang kita harus berhati-hati. Ini sangat persis dihitung dan dijelaskan oleh N.Hamilton G4TXG pada majalah komunikasi Radio 4/1991:RF hum fenomena, AC dari catu daya dengan 50 HZ modulasi LO (osilator lokal). Komponen sisi band dari 50 Hz kita mendengar sebagai hum. 50Hz kembali dari saluran pasokan listrik dan daripada menerima denganRX antena. Masalah ini digambarkan dalam buku pegangan ARRL persis. Solusi untuk masalah ini adalah untuk layar LO atau BFO dikotak tertutup. Solusi yang paling sederhana adalah kotak dari disolder PCB perdamaian-perdamaian yang adalah cara termudah untuk menyiapkan dan solder.Deteksi AM, fenomena yang saya diberitahu itu khas untuk DC Penerima. Fenomena ini terjadi di mixer karena mereka tidak mencukupi Mixer (detektor) linearitas yang mereka bekerja sebagai AM detektor. Demodulated sinyaldaripada memperkuat oleh AF Bagian Penerima DC. Fenomena ini terjadi juga di Super-heterodyne Penerima tetapi mudahmenghilangkan dengan jika kristal filter. Fenomena ini mengarah ke solusi dengan cukup selektivitas di depan mixer (demodulator). Selektivitas akan mengurangi angka dan kekuatan yang tidak diinginkan, keluar band sinyal. Switching mixer seperti 74HC4066,74CBT3253... juga akan menurunkan sensitivitas demodulations AM secara substansial. Mixer digital memungkinkan kita kita dapat langsungSambungkan antena ke mixer masukan tanpa masukan filter. Bayangkan tes ini dengan jenis mixer lainnya seperti DBM (dioda mixer). Mixer's kinerja AM sensitivitas menggambarkan dengan sinyal di mV input mixer yang akan menghasilkan sinyal yang tidak diinginkan di tingkat kebisingan (MDS).Baik nilai untuk mixer adalah 5-10mV atau sinyal S9 ditambah 50-60 dB mixer masukan. Solusi untuk masalah ini adalah utilitas yang baik linearitas mixer. Mixer dioda dengan dioda anti paralel yang memiliki LO pada 1/2 fs dan mereka memiliki penampilan penolakan AM terbaik dari mixer-mixer dioda semua tetapi saya tidak mempertimbangkan alasan jenis mixer ini adalah penampilan mereka yang tidak diinginkan lainnya.AF hum efek adalah bahwa AC 50 Hz langsung di AF Bagian Penerima DC. Memperoleh distribusi sangat berbeda bagi Penerima DC daripada bagi Super-heterodyne Penerima. 100 dB AF keuntungan adalah cukup normal situasi untuk realisasi receiver DC. Solusi untuk situasi ini adalah RX PCB skrining dan utilitas coax kabel untuk koneksi.Efek microphonic adalah asal-usul AF atau RF. Efek microphonic AF dapat diselesaikan dengan konstruksi mekanis RX dengan karet spacer. Efek microphonic RF cased oleh kebocoran LO mixer (demodulator) masukan. Sinyal yang kemudian mencerminkan masukan BP, perubahan mekanis atau mekanis shock berubah fase tercermin sinyal. Hasilnya adalah AF sinyal atau sinyal DC yang unbalancing mixer. Solusi untuk efek ini adalah utilitas dibangun dalam komponen kualitas tinggi, atau menggunakan dibentuk kumparan terutama di diplexer, sirkuit filter. -AF loop dan osilasi. Efek ini terjadi terutama ketika AF Keluaran amplifier berkendara pembicara. Keuntungan besar di DC receiver, keuntungan yang diperlukan untuk penggunaan praktis, akan menyebabkan perubahan tegangan dalam tahap sinyal yang lebih rendah dan deteksi mereka. Jika kita memiliki bagian yang buruk atau PCB sirkuit penempatan sinyal yang tidak diinginkan seperti parasit modulasi memperkuat ke tingkat kliping. Sinyal output tidak menyenangkan untuk mendengarkan apapun. Solusi untuk fenomena ini adalah untuk ketat mematuhi aturan untuk Desain AF baik dengan bintang tanah konfigurasi