[HN Gopher] Tiny Ten DSP-Based HF Transceiver
___________________________________________________________________
Tiny Ten DSP-Based HF Transceiver
Author : wglb
Score : 60 points
Date : 2025-03-02 14:34 UTC (4 days ago)
(HTM) web link (www.janbob.com)
(TXT) w3m dump (www.janbob.com)
| avidiax wrote:
| I have been wondering if/when we could get a direct synthesis SDR
| transmitter. Obviously the amplifier and filter stages will have
| to be discrete & analog, but to me it seems more elegant that you
| can software define any radio signal below 1Ghz or so and pass it
| to an amplifier.
|
| That doesn't detract from this project, which is quite an
| achievement for a single hobbier.
| 01100011 wrote:
| After working at a company using SDRs, I realized that a well
| performing SDR is a lot more than an antenna, a DAC/ADC,
| amplifiers and a processor. You still have analog paths you
| need to worry about and for many applications those aren't
| going to cover your 1GHz range. You need to worry about noise,
| amplification, signal fidelity, etc. You still need a good
| portion of what makes up a traditional radio. Sure, there are
| narrowband, low power SDR xcvrs and xmitters but that's not the
| same thing.
|
| That said, a long time ago I made a test fixture for a 6-bit,
| 12GHz DAC and it was cool to run it as an arbitrary waveform
| generator.
| RF_Savage wrote:
| The popular IC-7300 transceiver from Icom does that. Receiver
| samples the whole band and does downconversion in the digital
| domain (DDC) and same for the transmitter (DUC).
|
| On the hobbyist side there is the TRX Wolf by UA3REO.
| th0ma5 wrote:
| Sure, just do the Zeta SDR schematic in reverse, but like
| others have said you'd have to figure out the rest of the
| chain as well as a tone of filtering. I've transmitted with
| direct digital synth chips as well as rpitx which is
| literally bit-banging RF off of a pin on a raspberry pi with
| NTP sync even. Again, still had to do a lot of filtering, but
| with wsprrypi I was able to be heard one time in New Zealand
| from Ohio, USA without any amplification.
| ale42 wrote:
| How much RF power is actually coming out from the RPi
| transmitter? A few mW?
| th0ma5 wrote:
| Yes maybe a couple of hundred milliwatts at most.
| RF_Savage wrote:
| Naturally there needs to be filtering and some sort of
| analog frontend. My main point was that mainstream rigs now
| do direct sampling, instead of zero-if or superhet with dsp
| IF.
|
| And WSPR sure is magic, people do thousands of km with it
| off an rp2040 gpio pin.
| th0ma5 wrote:
| Yes sorry for the double reply I didn't know they were
| using the rp2040! Thanks for mentioning that !!
| topspin wrote:
| I'm not sure this is what you have in mind as far as
| "mainstream" rigs or architecture, but the FTDX-101D main
| receiver is a "narrowband SDR" system, as Yaesu describes
| it. Signal is downconverted through an analog chain
| including a narrow crystal filter before it reaches the
| 18 bit A/D+FPGA. And yes, it does perform very well,
| currently at the top of the "Sherwood" Third-Order
| Dynamic Range ranking, where it's been for about 5 years
| now.
|
| If I'm interpreting your view correctly, then I share it:
| there is a lot of performance to be had with a well
| designed analog front end, and the specs of the digital
| parts can be quite modest and still perform extremely
| well.
| nullc wrote:
| Quite a few radios are direct-- no intermediate
| frequency, just a set of band selection filters. The
| direct route does not quite hit the absolute state of the
| art in dynamic range, but it's close. IC-7300, IC-7610,
| Elecraft K4, etc. all have this design. I wouldn't be too
| surprised if one more generation of ADC improvements take
| it over the line. Certainly there is a lot more
| engineering might being put into better ADC designs than
| there is for superhet radios.
|
| Beyond being simpler on the analog side the direct
| conversion route makes spectrum/waterfall views of the
| whole band trivial. In theory radios could use this wide
| bandwidth for improved impulse blanker performance, but
| I'm not sure which if any do.
|
| Some (like the flex radio, and Elecraft) will do multiple
| in-one-band simultaneous receive with on each ADC using
| it... but (other than flex perhaps) the advantages of
| direct converting a whole band are currently under-
| utilized. Once they are I doubt there will be much
| interest in superhet even if the dynamic range isn't
| quite matched.
|
| I think the future of radio designs though will be
| finding ways to move the RF portion closer to the
| antenna(s), away from RF-noisy buildings, and avoiding
| expensive, lossy, and annoying coax runs.
| th0ma5 wrote:
| Sure, just do the Zeta SDR schematic in reverse, but like
| others have said you'd have to figure out the rest of the chain
| as well as a ton of filtering. I've transmitted with direct
| digital synth chips as well as rpitx which is literally bit-
| banging RF off of a pin on a raspberry pi with NTP sync even.
| Again, still had to do a lot of filtering, but with wsprrypi I
| was able to be heard one time in New Zealand from Ohio, USA
| without any amplification.
| mschuster91 wrote:
| > Again, still had to do a lot of filtering, but with
| wsprrypi I was able to be heard one time in New Zealand from
| Ohio, USA without any amplification.
|
| Hope you got a QSL card out of that kind of DX effort. What
| antenna did you use?
| boxerbomb wrote:
| I would imagine he was talking about running WSPR.
| th0ma5 wrote:
| Yes WSPR ... The acknowledgement of contact was online. I
| had an MFJ antenna tuner but it was just a long strand of
| wire lying over the roof maybe 14 gauge? Slim. Something
| like 100mw output power? 200mw Maybe? It ran for a couple
| years unattended and was regularly heard east of the
| Mississippi and sometimes with some regularity in Europe.
| picture wrote:
| We've been in the age of direct RF for a while. The new
| cellular base stations that Nokia makes are literally eight
| RFSoC chips connected to 64 power amplifiers. You can get one
| for yourself for pretty cheap:
| https://www.realdigital.org/hardware/rfsoc-4x2
| _benj wrote:
| I loved the article! Even though I only understood about 1/3 of
| the technical details, I was honestly quite amazed at how
| "simple" was producing RF! The guy is using "sound" at 48kHz to
| produce the signals needed and then a Si5351A (signal generator
| for up to 200MHz or so controlled via I2C) to produce RF. I'm not
| sure, or don't understand yet how the RF is being modulated, but
| conceptually is understandable! DSP is a field I want to dig
| deeper into, specifically DSP as it pertains RF.
| picture wrote:
| The reference signal generated by Si5351A is used to clock two
| flip flops which I believe are used to generate a 90deg
| quadrature local oscillator (LO) which enters a dual 1-4
| multiplexer acting as a Tayloe quadrature mixer. And as you
| know, the nonlinear switching action introduces frequency
| products and allows frequency conversion.
|
| This is a pretty clever system. The RF is low enough frequency
| that faster logic chips can be used effectively. I recommend
| getting yourself a cheap receive-only SDR for around 15 bucks
| and play with GNURadio, if you want to get more familiar with
| DSP for telecommunications/radio detection
| _benj wrote:
| Thanks! I think the limitation is in my knowledge and not in
| the article or schematics!
|
| I have a rtl-sdr and I've played with gnu radio, but the
| signals that I had to explore were very limited! Apart from
| few remotes for fans and stuff around the house I only had fm
| radio and little more.
|
| What I find very interesting from this is the possibility of
| taking a Si5351A breakout board, configuring it with I2C (I
| can do that), modulate it with something like audio and a
| mixer (I can code that... maybe) and plug that directly,
| likely through and attenuator, to gnu radio!
|
| It would certainly be a lot easier to get a sdr transmitter,
| but I wasn't aware of the possibility of modulating a Si5351A
| with a "simple" signal like 48kHz audio!
| gherlein wrote:
| Here's another: https://www.4sqrp.com/T41main.php - I just bought
| one that someone else had assembled. It's 100% open so you can
| buy boards and make your own, but the kits themselves are no
| longer available. I am thinking of ordering a set to take the
| design further, as a learning exercise.
___________________________________________________________________
(page generated 2025-03-06 23:02 UTC)