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| Any Shortwave Radio Tips for a Noob Considering the Hobby? |
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| fourfathom:
--- Quote from: edy on December 09, 2019, 05:47:59 pm ---You are correct, I do not believe there is a BFO in the Tecsun. --- End quote --- Back to that Tecsun, the marketing blurb says: "Special design of SSB demodulation functions, can receive amateur maritime communications and personal radio". So I think we should expect that you will be able to receive SSB. Please let us know how this works for you! We can give you some pointers to help you find SSB signals to monitor. |
| PA0PBZ:
--- Quote from: fourfathom on December 12, 2019, 07:02:12 pm ---Back to that Tecsun, the marketing blurb says: "Special design of SSB demodulation functions, can receive amateur maritime communications and personal radio". So I think we should expect that you will be able to receive SSB. Please let us know how this works for you! We can give you some pointers to help you find SSB signals to monitor. --- End quote --- I found this only on Amazon and it must be a mistake. In a few reviews (eham.net) they mention it has no SSB capability and since this is a direct sampling radio you can't build an oscillator on the IF frequency (there is no IF). Also, the tuning steps are way too big for SSB. |
| fourfathom:
--- Quote from: PA0PBZ on December 12, 2019, 07:20:26 pm --- --- Quote from: fourfathom on December 12, 2019, 07:02:12 pm ---Back to that Tecsun, the marketing blurb says: "Special design of SSB demodulation functions, can receive amateur maritime communications and personal radio". So I think we should expect that you will be able to receive SSB. Please let us know how this works for you! We can give you some pointers to help you find SSB signals to monitor. --- End quote --- I found this only on Amazon and it must be a mistake. In a few reviews (eham.net) they mention it has no SSB capability and since this is a direct sampling radio you can't build an oscillator on the IF frequency (there is no IF). Also, the tuning steps are way too big for SSB. --- End quote --- I agree on the tuning steps, although for channelized marine SSB they might be OK -- assuming that the radio oscillator is accurate. Since the diagram in the manual shows a 32KHz xtal as the SDR reference clock, I would guess that the accuracy isn't all that good and you would need a "clarifier" (fine-tuning) to make it usable on SSB. It is certainly possible to demodulate SSB on an SDR radio, the BFO is implemented in DSP. But you still need 100Hz or finer tuning steps for non-channelized SSB. |
| edy:
I've been thinking more about sidebands. I understand beats fairly well, I can visualize how 2 frequencies that differ slightly will interfere and because they are slightly off they will originally constructively interfere and produce 2x peaks, and then a moment later they will be out of phase (180 degrees) and will cancel out completely. So by combining 2 very-close frequencies you get the beat pattern... and the beat frequency increases as the difference between frequencies gets bigger.... and I have intuitive experience with this as well with tuning guitar strings as you try to tune adjacent strings by playing same note and listening for the beats to try and minimize the beats. To understand the sideband production (when modulating a single CW) I am trying to intuitively understand what is happening, so I flipped it BACKWARDS... and imagine what would happen if you combine a sideband with it's CW. Say if I combine the LSB with CW, then I would pull out the "beats" which in this case ends up giving us the actual audio signal. Similarly, I can combine a USB with the CW and it will create "beats" as well, which is the audio signal. So I understand it in terms of demodulation.... how the beats will come out of combining either LSB+CW or USB+CW. The other way is harder to wrap my head around (how combining CW+modulation generates beats). This video is great to demonstrate it: I am going to try and use Audacity to generate waveforms and combine them. I can generate a tone of a very high frequency (CW) and then a lower frequency tone (modulation) and I believe there are Nyquist filters/functions or coding you can do in Audacity to let you modify one wave using the other. Then I can run it through a spectrum analysis in Audacity and see if it produces the kind of peak patterns that we see in that video. I should also be able to programmatically create a WAVE file. If I can make a RAW file which is essentially just a string of 16 or 32-bit values, I can write out a sine wave and modulate it all in software. I'll have to see the format for writing out RAW wave data and then should be able to write a small C program to do it and test out different things. Regarding the Tecsun, here is the spec sheet: https://www.tecsunradios.com.au/store/product/tecsun-pl310et-multi-band-radio/ It says it has selectable IF bandwidth. I don't know what that exactly means. Maybe there are some software-enabled DSP functions for specific frequency ranges that give you some SSB capability. I don't know. Seems to be all done by the chips and there may be a PGA in there with custom firmware doing stuff. I have no idea how these radios are built and haven't yet looked at the block diagram or schematic. |
| Bud:
--- Quote from: fourfathom on December 12, 2019, 07:02:12 pm --- --- Quote from: edy on December 09, 2019, 05:47:59 pm ---You are correct, I do not believe there is a BFO in the Tecsun. --- End quote --- Back to that Tecsun, the marketing blurb says: "Special design of SSB demodulation functions, can receive amateur maritime communications and personal radio". So I think we should expect that you will be able to receive SSB. Please let us know how this works for you! We can give you some pointers to help you find SSB signals to monitor. --- End quote --- What is "amateur maritime communication" ? |
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