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DSB transceiver for Digital mode
开云体育May I call it D4D - DSB transceiver for Digital mode? This 1-watt DSB transceiver will provide lots of fun of building and operating. The VOX circuit will provide even more convenience to the operator. Thanks to the strong capability of digital mode and computer, this rig is not a toy. You can easily make FT8 contacts of 300-1500 miles range with a moderate antenna like full sized dipole ?or EFHW.The photos are for the prototype based on CRK-10A enclosure. It looks quite close to the final version. We will run testing in the following weeks. The initial test looks promising. We plan to take orders in about a month. We will start with 7074 version for FT8. The price will be very reasonable. Stay tuned and spread the word if you guys are interested. Thanks, Adam |
开云体育Folks,Let’s use this thread to update the status. The test is done. I have tested both 7074 and 14074 radios. I need to update PCB to include a minor fix. I will accept order and start to ship after Hamvention in May. I have lots of work to do considering my limited spare time. Compared with the open schematic, I have modified several areas to improve TX signal purity and frequency stability. The added VOX circuit works as planned. I understand now that the DSB circuit concept I have adopted has some potential issue to cause self-oscillating. It seems that my fix is effective and still simple. I can build this kit in a bit more than one hour. If you take time, you can enjoy a whole evening to build and test this rig. I have to standardize the name of this rig: D4D, no matter what it was called, either DSB FT8 BD6CR, FT8 DSB VOX or else.
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开云体育Technically it is possible. Just change the crystal and I might be able to customize it. However, we will need to consider the unwanted LSB signal will go into FT8 spectrum and it might cause interference although the power is still QRPp level.If we want to experiment, just pull high the crystal a bit to see how high it can go, maybe 7075 or 7076 but not easy to get 7078 for a HC49S holder crystal. Thanks, Adam
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开云体育Jim,I would leave it for customers’ modification. We have added a crystal in the front end as the filter. We will have to switch both. Thanks, Adam
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Folks,
I have placed order for PCB two days ago. The first batch is 350 pcs. I have finalized the parts value and will place order for parts tomorrow. The RF output is 1-watt at 12V for 14.074MHz, and a bit bigger for 7.074MHz. The spurious suppression is better than -50dBc. I hope to start kitting for the first 5 pcs on May 4. If it goes smoothly, I might take order to ship these kits early, so you can send a few test reports ahead of time than the usual customers. Stay tuned and I hope you will like it. Thanks, Adam |
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Hello. Cut the crystal around 1mm around the crystal, scratch the crystal very carefully, just a little, and measure it frequently. It will be a slight increase of 30 maximum 100kz. Verified method, step by step.Mircea-YO9IOF
On Wednesday, April 24, 2019, 7:46:13 PM GMT+3, Adam Rong <rongxh@...> wrote:
Folks, I have placed order for PCB two days ago. The first batch is 350 pcs. I have finalized the parts value and will place order for parts tomorrow. The RF output is 1-watt at 12V for 14.074MHz, and a bit bigger for 7.074MHz. The spurious suppression is better than -50dBc. I hope to start kitting for the first 5 pcs on May 4. If it goes smoothly, I might take order to ship these kits early, so you can send a few test reports ahead of time than the usual customers. Stay tuned and I hope you will like it. Thanks, Adam |
开云体育Folks,This is a bit history for D4D: A simple QRP transceiver kit for FT8. D4D stands for DSB transceiver for Digital modes. It is a Double Sided Band transceiver kit designed for digital modes, especially for FT8. If you have chance to try FT8, you will be amazed by the strong decoding capability due to the communication protocol, digital signal processing and software. I still remember clearly a YouTube video by W6LG who communicated with a bulb. I started to think how much the transceiver could be simplified if you have a moderate antenna like a full sized dipole or EFHW instead of a bulb. A DSB transceiver is much simpler than a SSB transceiver, however it was never used for FT8 as far as I know. I did some experiments on my Choc perf board, a specially designed perf board for RF circuit experiments. I started with a direct conversion receiver for FT8 and it worked okay. Then I built a DSB transmitter and the transmitted signal can be decoded. By referring to the DSB designs of AA7EE, VK3YE and ZL2BMI, I combined them using only one NE602 and a PTT switch and it gave me success to make a few FT8 QSO’s. Personally I really enjoyed it because a manual PTT switch will save power consumption and circuit complexity, but you will need to well sync with computer, although it was not really a problem for me. Per request from a few hams, I found a VOX control circuit and modify the hold time to be compatible with FT8, and I put them together and made a few improvements on the signal purity and frequency stability, and it finally became our D4D. Do we have to worry about the unwanted Lower Side Band? Maybe, but for a transmitter of 1-watt, it is not really a big problem. Is it just a toy for a transmitter of 1-watt and only half of the power will be effective? Not really, as I can easily make a few QSO’s as far as 1500 miles range for 40-meter band. Thanks, Adam
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Folks,
I have put together a final version and it worked perfectly. Now I accept order for beta testing. ?I will ship 3 kits of 7074 by May 6. If you join beta testing, you will need to keep secret before Hamvention debut. You will have time and equipment to build and test the kit and publish a test report. If you have a popular YouTube account or web site, please let me know so you will have priority. Please contact me offline. The MP version will be shipped on May 20. Thanks, Adam |
开云体育Folks,Well, it was leaked by . Check it out for now, although some data might be modified later.
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Folks,
I have decided on all the key parts, and purchased most of them. The relay reliability is very important, so I have chosen Zettler, the same brand used in Elecraft K2 kit I have purchased before. The ferrite FT37-43 is produced by Fair-Rite and purchased from Mouser. All the capacitors under 1uF is produced by Torch, the top brand in China. I will announce the product via my web site in the May 11-12 weekend and start to take order. The first order will be shipped no later than May 20. If you wish to get some assembled kits, please let me know ahead of time. Thanks, Adam |
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Adam,
Glad to hear about your progress.? Just a few questions. - What are the dimensions of the PCB (or case)? - Do you recommend using the heating resistor especially on the 20 meter version?? Was the stability still ok without it?? How much did stability improve with the resistor? -? Did you experiment using a higher gain LM386 or other audio amp instead of the single transistor audio amp circuit that you're using?? If you did, was there much difference in performance? Thanks again for all your efforts! 73, Ron (KA3J) |
开云体育Ron,Thanks for the questions. 1. The PCB size is around 100x64. 2. The heating resistor is recommended for 14MHz. It is really a balance between short term and long term but I see overall improvement. This idea is very rare so I need some more experimentation from you guys. 3. The real concern is not sensitivity but SNR. Since the output impedance is several hundred ohms, by using one transistor, the signal is big enough to give 40-50dB, already bigger than recommend 30dB. My previous version was LM386 and I don’t see much difference. However I have to say that the receiver SNR report ?is noticeably worse than big radios. I can easily improve receiver itself but considering transceiver overall, I have to sacrifice a bit. The receiver performance is reasonable to match one-watt DSB transmission. You have to balance. Thanks, Adam
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Adam,
Thanks much for your responses. When making comparisons with a big rig, how much worse was the received SNR report?? With the little rig, would you say it was 5 dB, 10 dB, or 15 dB worse?? Also, how many fewer decodes can we expect - 25% less, 50% less?? ? Since I'm planning to put the rig in an enclosure with a Raspberry Pi, there is going to be plenty of heat around.? So once things warm up, do you think this would help with longer-term frequency stability and make it unnecessary to use the heating resistor?? ?Of course, I'll be more than happy to experiment and share my results.?? 73, Ron (KA3J) |
开云体育Ron,SNR is 5-10 dB worse. However, I found that I only can make QSO with radios of -15dB SNR or better, so I think this is not a problem. Same as QRP communication, you have bigger chance to QSO with bigger signal. You may have interest to hear more signals even you don’t have chance to make QSO, but if I improve the SNR, I have to sacrifice RF output power to avoid self-oscillating. This is the limitation of using only one NE602 for TX and RX, and I chose to sacrifice RX performance to make the transceiver more balanced. Heating is a complex question. It is documented that if the ambient temperature is around 50 C, the thermal drift of an AT cut crystal is minimal. Adding heating resistor is just to complete the heating progress in short time. There is just another way to help you if you really need help, especially on 20m band in which specific percentage of drift will cause bigger amount of drift in Hz. Also the heating power is only available during RX, so it is kind of compensation during RX. Thanks, Adam
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Adam,
Thanks for your helpful, informative responses. So it sounds like the 40 meter version may be significantly more stable than the 20 meter version because of the lower frequency crystal.? In addition, the 40 meter crystal doesn't have to be pulled like the the 14.070 MHz crystal which eliminates another possible source of instability, correct?? Does this mean the heating resistor is more optional for 40 meters? Also, what is your source for the 7.074 MHz crystals? Thanks again for your help and I'm glad to see we can order now! 73, Ron (KA3J) |
Jim
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