RF mixer is a key building blocks in transceiver design. I tried several popular active mixer such like SA602, TA7358, MC3362. I never tried DBM until Om Farhan (V2ESE) introduce the BITX and its very success. Then I tried to build the BITX also by my self. I amazed its works on the first try. Based on my experience and comparing to other active mixer, for me BITX with its DBM is very stable. The design is straight forward, simple and easy to understand, the schematic actually describe basic function of each block on transceiver design. In my believing by choosing high quality component on BITX we can build high quality transceiver. In other case using low cost component we can build low cost transceiver without loosing the quality too much. This design is very compromise. Of course if your target is middle bass or high quality audio, crystal clear audio, do not choose BITX. There’s a lot transceiver with build in DSP. What do we expect on 3KHz bandwidth? I lost my hearing capability for frequency upper 3KHz when I work at utility department that assign me to handle 8 unit 1MW SKF and 2 unit 0.5 MW Niigata genset. So for my ear BITX is more than enough.
Why I see BITX is simple and straight forward? let we see heterodyne RX diagram below :
This diagram is really similar for each block what is inside RX chain BITX.
please visit Om Farhan web for circuit description http://www.hfsignals.com/index.php/2017/11/23/bitx40-circuit-description/
and a posting from https://hackaday.io/project/20067/logs, and also a lot BITX discussion on internet about it.
I capture what Om Farhan said about this half of bidirectional amplifier circuit (http://www.hfsignals.com/index.php/2017/11/23/bitx40-circuit-description/). This circuit is repeatable 6 times similar, may be little bit difference on some stage coupling.
For me BITX is a good entry point to learn and to get a little more exposure about RF design without too much doing math calculating. We just need to choose or put alternative component, give some additional of feature and try and try. You can easily modified or enhance but I cannot found any better explanation about building transceiver like what Om Farhan did, the simplicity and functionality.
Two thumb up for Om Farhan!
Setelah riset lebih lanjut disela-sela kesibukan membenahi lagi workshop yang telah 2 tahun ditinggalkan berikut adalah hasil dari v1.0 HBR1HF. Seperti disampaikan pada postingan sebelumnya, fokus HBR1HF adalah “Low Cost” dengan fitur minimal, display minimal dan terbatas.
Keuntungan dalam membangun sesuatu yang “mono” adalah proses tunning dan adapting hanya perlu konsern pada satu band saja. Ukuran yang kompak (150 x 150 x 54 mm) cukup kecil dan mudah dibawa-bawa membuat HBR1HF cocok di operasikan portabel. Walaupun dengan ukuran yang kecil tadi, HBR1HF bisa mengeluarkan output hingga 50 Watt pada 13.8V, 50 Ohm dummy load pada mode CW. Berikut penampakannya :
Bila rekan-rekan berminat, semoga awal tahun akan bisa diperoleh di tokopedia atau bukalapak serta eBay untuk rekan Internasional.
HBR1HF didesain untuk mengisi kekosongan perangkat bagi pemula yang ingin aktif di HF band. HBR1HF dibangun dengan kesederhanan, sehingga diharapkan bisa memberi ruang bagi pengguna untuk meningkatkan performance dan atau memodifikasi perangkatnya sendiri. HBR1HF bisa dikembangkan kemudian dengan mengganti mixer utama, dikembangkan audio amplifier dengan output yang lebih besar, ditingkatkan RF power out dan sebagainya. Bila diingikan bisa juga di kerjakan pada band amatir lain (80m/20m) dengan mengganti nilai-nilai komponen pada BPF dan LPF nya. Semangatnya adalah memudahkan jalan untuk bereksperimen tanpa menjadi terlalu rumit.
*. RTCMono controller (Si5351 + 16×2 LCD) dengan firmware khusus monoband
*. 40m band (optional 80m/20m)
*. BRITX exciter
*. 50 Watt TX power out (2SC1162-IRF510-IRF530)
*. Dimensions 5.4cm x 15cm x 15cm.
Semoga sebelum akhir tahun sudah bisa mengudara.
*. BRITX Based
*. Front End RF gain using 2SC2570
*. Front End RF attenuator
*. TX RF attenuator
*. ADE-1 main mixer (detachable)
*. Detachable ladder filter
*. CW generator/Key PTT delay on board
*. AGC on board
*. Band Pass Filter on board
By replacing main mixer with ADE-1 we can get very good carrier suppression, increase sensitivity, and we can get more TX power on almost band. We also added crystal ladder filter adapter, so it can be upgrade next. You can replace the crystal with your mechanical filter (please take note the impedance matcing), or you can make variable BW filter by using varicap diode.
We decided to use separate RF amplifier board with LPF on it. We hope we can increase the power out, but still using the low cost MOSFET.
YD1OSC (ex YD6DEK)
Hambuilder HBR10HF using RTC03 as controller with 3.2 (320×480) TFT LCD. This item worked very nice, good color, viewing angle, speed (using 16 bit parallel data). But the main problem is the availability is a night mare. I using this TFT since early 2016 when I started to build the RTC03. Until now, this TFT already have 3 difference controller in market, with 3 difference firmware and specification and the worst is, seller from China that I bought this TFT did not know and did not help what kind controller or even give me any datasheet. I must find out by my self how to make this LCD works.
its look same but they have difference
when you look at their back side its HX8357C, V2.0 and blank, its all false
The HX8357C using ILI9481, the V2.0 using HX8357D and the blank one using HX8357C.
They need difference firmware and have difference command, and what I want to tell here is they have difference habit and speed. The blank one do not need hardware reset, but the other one intermittent required. This habit make your RTC03 sometime show the white or gray or even blank display on start.
How to solved this problem? actually is very easy (this bug already solved on our production line), please check the image below. We just need to added R-C reset delay. please see the picture below
and implemended like this on your RTC03, I choose R 10K and C 100nF.
Then if you get your RTC03 with intermittent gray or white screen on start you can applied this solution.
After a long rest, its get back
One feature on HBRAA3 Antenna analyzer is a filter response plotter.
Its worked based on
*. Si5351 as freq synthesizer
*. AD8307 logarithmic amplifier
by generate some range of frequency , send it to input port of a filter, then let AD8307 amplify the output port, then read the value (25mV /dB) by using micro controller ADC, we can draw the response on LCD. This feature very help for analyze crystal ladder filter, BPF and LPF of any transceiver.
an example 10MHz ladder filter plot response (non scale)
Similar condition with HBR10HF some buyer report carrier leakage on HBR4HF, same proble with his brother HBR10HF, BFO level is too big injected to modulator. Here’s the solution :
*. Replace BFO coupling from RTC01C with 100pf value
*. Tunning the preamp trimpot
*. Tunning the carrier balance
*. Adjust gate bias voltage (Vgate) into 3V
How ever please take note, power of the transceiver considering many thing not just increasing the final stage value. We must consider also the cabling, switch relay, PCB track and etc. HBR4HF and HBR10HF not designed to produce big power.