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BITX in 2m band
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Greetings to fellows BITX'ers.
The other day I was testing a VCO for the range of 144MHz with the interest of making work the BITX in 2m. The VCO oscillates from 125 to 145MHz approximately with a air coil. I use 2N2222 transistors, but I soon realized that the BFR90 worked quite better. It is mounted using the "manhathan style", with a copper panel like ground and "ugly" assembly. Then, the PLL oscillator works perfectly without no modification to this frequency, what doesn't stop surprising me. But, the stability is poor due to the precarious assembly, however it is working without problem. The following step was to inject the 134MHz signal (I use a FI of 10MHz original) to the amplifier of the original VFO made of two 2N2222, the amplifier works and the circuit was able to transmit and receive. However a output tank syntonized to 144MHz didn't exist in this test, the signal was very weak. Once installed a tank of 3 coils and an amplifier with a BFR90 I succeeded in extracting the 144MHz signal, not without an adjustment very critical and delicate. The BITX transmitted and received in 2m USB!! I could not have made more tests, neither place a front end syntonized to 144MHz :-( . If the time permits me I follow investigating, because the topic seems very promising. I ham working in a multiband/multimode design (80m/40m/20m/15m/10m/6m/2m) (AM/FM/SSB/CW). The idea is to carry out three PCBs: SSB GENERATOR; PA, LPF, BPF; Microcontroller, PLL and VCOs. The work possibly is never concluded for time problems, but at least it could remain like contribution to whom he or she cheer up to finish it. I put these schematics in the files section as soon I can. I like to ear coments to this developement. Greetings EA7ARX, ex EB7HPM/EC7ALV |
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Paolo Cravero as2594
Hi
Great to read about your BITX developments! I have one concern, though: will it be possibile to efficiently filter out unwanted harmonics +-n*10MHz at 144 MHz? I think VHF&up transceivers use higher modulation IF or a different generation method. Just my thoughts, Paolo IK1ZYW -- | QRPp-I #707 + www.paolocravero.tk + I QRP #476 | | SpamAssassin-based email antispam/antivirus solutions | \ Italian/English-to/from-Croatian translations / \ Skype: pcravero / |
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--- In BITX20@..., Paolo Cravero as2594 <pcravero@a...>
wrote: Hifilter out unwanted harmonics +-n*10MHz at 144 MHz?different generation method.Good... good question. ;-) The Yaesu FT-290R have 4 passaband filters sintonized at 144MHz with the aid of varicaps as output of mixer (it has also a ring diodes mixer), it has a 11MHz FI, then I suposse this is not problem, having some narrow passaband filters (four etapes minimun). The consecuence of this is that the sintonization range will be narrow also, but this is not a problem. I want to use only at 144.300 +- 50KHz. ;-) I do not use varicaps for sintonizing.. I make a tranverter for 28MHz to 144MHz a year ago and it also have a 4 coil passaband filter little trickly to adjust. But no much problem afterthat. Howhever I not have made yet the tests. The 4 coil passaband filter must be enclosed in a box, and the coupling must be soft. A coil near the other coil assures soft coupling. It woks, as work for my transverter a year ago. Thank You for your coments. Greetings Manuel EA7ARX Just my thoughts, |
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ajparent1
Hello,
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Harmonics resulting from mixer operation are not a problem if circuits are run linear with attention to correct signal levels. Attention to filtering is a requirement and at 2M leads must be short and use of shielding can be helpful. I have a old and still very good Icom IC245 (nearly 30 years old) 2M CW/SSB/FM that the IF is 10.7mhz for SSB and CW. However if the builder can use a 16 or 20mhz IF that is helpful. It is possible to build a good SSB filter at 20mhz. Allison KB1GMX --- In BITX20@..., Paolo Cravero as2594 <pcravero@a...> wrote:
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ajparent1
Hello,
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I have also done transverter for 2M in the past as well as 2m RX designs. A good filter for 2m can be done with 3 coils of helix design using aperture (window) coupling. Constuction is a 3 cell box using 2 sided copper clad board material. I have also found it convenient to develope for VHF/UHF using modular construction. For BITx this would be the audio, modulator, carrier osilarot and IF stages on one board and encased then later stages in boxed. Connections between boxes is with coaxial cable for RF. The whole radio becomes a box of boxes. This appears difficult but allows good shielding and makes stage by stage testing easier. Good luck with 2M. FYI: I have tested early stages of the BITx for 6M without power amplifers. With only 1mW (.001w) the range was only a few miles but the signals sounded good at the other end and recieve performance is as expected. More work is to build the power amplifier chain and enclose it. Allison KB1GMX [FN42hh] --- In BITX20@..., "eb7hpm" <msraya@t...> wrote:
--- In BITX20@..., Paolo Cravero as2594 <pcravero@a...> |
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