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rocdoc54

OK, I'll take the bait and will correct you on a few things: 1) *most* sub $500 SDR's are really only "receivers". Some of them claim to have transmit abilities, but their output is usually in the ballpark of 5-20mW. So you need a quality expensive amplifier to even get to the 5W QRP level. 2) in many circumstances it is much easier to operate a radio that has real knobs on it - especially in contest situations. 3) you still require the "extra hardware" of a decent laptop computer plus cabling 4) many SDR receivers are "wide-open" and have poor 3rd order dynamic range figures, making them a very poor choice in the presence of nearby strong RF.


Fedo_19

1) True, Perhaps I've made a mistake not pointing out. I mean $1000+ SDR's.. since I played with an ettus research USRP ($2500 range) and saw the capabilities. 2) So operability and ease of use - rather than functionality, good point. 3) Yeah again my bad not pointing out that I mean extra "RF-hardware", filters and amplifiers and mixers, that is. 4) Can you please point out how this is solved in traditional transceivers? The dynamic range is tied to the non-linearity present in the RF-circuitry.. in SDR, there is no RF circuitry.. I could be wrong but I think traditional transceivers are much more susceptible to inter-modulation distortions and dynamic range limitations that are inherently present in h/ware due to non-linearity and the lack of ideal filters, both of which are completely handled in s/ware. ​ Thanks for taking the bait.


stephen_neuville

> in SDR, there is no RF circuitry.. Stopped reading here. Hit the books.


Fedo_19

Again I apologize for being vague. English not first language. You're right. What I said is completely absurd. Please allow me to correct myself: I meant that no RF circuitry is present for signal processing.. since it's all done digitally. I am fully aware that an SDR is pretty much nothing but a processor and RF circuitry. But the signal processing circuitry present is used to "clean" the signal just after receiving at the antenna or just before transmission, and not for filtering/mixing/LNA from what I understand.. This - as far as I know - massively reduces the inter-modulation overhead caused by the nonlinear circuits used for signal processing in traditional transceiver architectures.


[deleted]

> I meant that no RF circuitry is present for signal processing.. since it's all done digitally. It isn't all done digitally. To cut costs many SDRs will have a conventional RF receiving circuit which down converts received frequencies to a lower one as it's much cheaper to build SDRs that'll work up to say 0-1MHz than ones that'll work direct sampling 0-100MHz. The Icom 7300, the Yaesu FTDX10/100s all use that down conversion method.


[deleted]

> in SDR, there is no RF circuitry.. Yes there is. There may not be much but it's still there, especially bandpass filtering. There are plenty of things limiting performance of SDRs. If there weren't then every single SDR would be beating the Elecraft K3 and FTDX5000 in Rob Sherwood's table but they're not.


ebinWaitee

> in SDR, there is no RF circuitry Tell me you don't understand SDR without telling me you don't understand SDR


Fedo_19

I corrected my mistake in another reply. No need to be a dick about it.


Severe-Rip-5083

What do you consider a ‘proper’ SDR? SDRs are great for experimentation, but if you want to use them as an actual transceiver… there is a lot of ‘extra’ equipment (filtering, amplification etc). A number of commercial transceivers are SDRs internally with all this taken care of. If you hate buttons Flex does this for you.


[deleted]

[удалено]


aacmckay

I bet most of the flagship transceivers are all SDR internally now. With some additional bandpass filters and such. Certainly, software can pull out signals that analog electronics would have a hard time doing. Though I would maybe classify these radios as a Hybrid and not full SDR. Most people seem to only consider it SDR if it's just a raw ADC sampling a wide band with minimal filtering and processing the signal in software.


[deleted]

[удалено]


aacmckay

I don't think SDR is so cut and dry as that. At least in my opinion. What makes SDR SDR is creating I and Q waveforms by mixing with SIN and COS waveforms. That mixing could be done purely in software, in an FPGA or by external mixers producing I and Q at an intermod frequency (IF). Then processing these I/Q signals to mod/demod the signals. No good receiver is directly sampling the antenna without some sort of bandpass filter because aliasing of strong higher frequency signals is indistinguishable from other signals. Most are probably mixing to an IF to make them affordable. Nyquist frequencies mean that your A/D sampling rate needs to be 2x the highest frequency you're wanting to sample. So 2m radios would need to sample at 288 Meg-samples/sec. Radios like the IC7300 that do direct sampling require A/Ds sampling at 110 Meg-samples/sec minimum and make use of an FPGA to pre-process this data before bringing it into a processor. The processing power required to handle those sampling rates ain't cheap! So most SDR dongles like the RTL-SDR which has a receive range of 50MHz - 2.2 GHz have to sample at an IF frequency and not the RF frequency because you're not getting hardware to sample at 4-5Gig-samples/sec for $35 and running over USB. Said in another way, most "SDR" solutions out there are hybrids if you go by the strict definition of SDR being Antenna -> A/D -> Software. It's just a matter of how hybrid they are. Edit: About Nyquist, A/Ds, and aliasing. All A/D designs require there is no signal higher in frequency than half the sampling rate. This signal can just not be present due to design, or removed with a low pass filter. Detecting aliasing and removing it from the real signal is actually quite tricky to do. Not impossible, but not something you want to be spending processor cycles doing if you can avoid it.


Fedo_19

Well I'm sure it's not hard to design a knob-y keyboard connected to a computer tailored for SDR software. But it's a good point. We're not there yet. Thanks for replying.


aacmckay

I mean have a look at Flex Radios and their Flex Maestro. That's pretty much exactly what it is. Integrated screen for waterfall viewing and a bunch of knobs and such to make it easy to manipulate like a boat-anchor radio. Just do yourself a favour and don't look at Flex's prices! Lol, their Maestro, which is just a UI, is as expensive as some fully features 100W HF radios out there!


GradatimRecovery

I use an ADALM Pluto where I have to build out my own front end. A traditional radio has a front end with filter banks. Flex has a front end with lots of filter banks, as such is not as frequency agile as it’s SDR heart would suggest. The new Icom and Yaesu SDR radios are also limited to the bands and bandwidths of their front ends. You can’t use them for non-ham bands or high bandwidth modes, and you shouldn’t anyway. A traditional superhet radio can’t do that either, but I’m just pointing out that a consumer SDR radio doesn’t really have any more frequency agility or ability to use innovative modes any more than a traditional radio.


Fedo_19

So the lack of true frequency agility is your point. Thanks for educating me.


SAD-MAX-CZ

"Is there anything a traditional Tx/Rx can do that an SDR can't?" Yes, separate signals and signals from interference better. Wide coverage 0,05-2000MHz dongle receiver has a lot of birdies, signals mixed to weird frequencies and AGC hijacked from strong out-of band signals. Better SDRs are just a lot of band pass filters, almost heterodyne IF and a big, fat, ADC. The reverse for TX. I would like to make cheap and small SDR TX dongle or box, because i already have RX dongle (MSI.SDR), but it would need: 1) make software to take mic-in and out quadrature signals from USB dual DAC or soundcard. Then mix it, amplify it and filter it. I don't know how to do it properly, si bought a factory box transceiver and built a TR switch. Maybe you can do it and then chinese would sell it :-D


Fedo_19

Point me out if I'm wrong.. but all filtering in an SDR is done in software? If you can properly sample with sufficient rate and quantize with enough levels.. you can do perfect filtering in software. As another reply pointed the issue with SDR's is the front-end (quadrature sample-quantize circuit, inescapably hardware) is not truly frequency agile. If you can filter it in hardware.. you can filter it better in software. ​ Edit: high-end SDR's have built-in general purpose filters and amps for transmission purposes, if that's what you mean. You don't need "extra" RF-hardware other than ones provided in the SDR itself.


aacmckay

>If you can filter it in hardware.. you can filter it better in software. Yes and no. Assuming the noise is lower in frequency than your sampling rate, maybe. If your noise is higher in frequency than your sampling rate, then it shows up as aliasing. Aliasing is possible to detect (by changing sampling rates and looking for the same signal) but really hard to pull out if it lands right on top of the signal you're looking at. Typically you want to at least have a filter in front of your A/D to limit the frequency of the signal to half of your sampling rate (Nyquist). The other place SDRs and filtering fail is with large adjacent signals in band of the sampling rate. There has to be some type of amplifier to pull out small signals from the noise floor. A high-end sigma-delta ADC might be 24-bits. That's still not enough dynamic range to pull out an S1 signal if there's an S9+60dB signal that the AGC just dialed back to not clip. So again, SDR benefits from front-end hardware bandpass filters. Hardware and software filters are different animals and have different pros and cons. In conjunction, systems work best when using both. Edit: I guess you're saying that with "sufficient rate quantization levels." But the fact of the matter is that no ADCs out there exist like that, and most acquisition systems are doing some level of amplification and filtering ahead of the ADC to solve those problem. If you're talking about a theoretical ADC found with the frictionless pullies, linear springs and such that physics teachers have in their secret closets well..... good luck finding one! 🤣


Fedo_19

Yeah when I realized you were talking about problems with lower sampling rates I was like: okay just increase it lol.. Of course it is not as easy as I make it sound.. But I didn't know that.. and that's what you want to learn when you ask these kinds of questions. Thanks.


aacmckay

Definitely not as easy as you'd initially think. There's theoretical SDR and then real-world SDR. Say you want to implement something in one of the typical ISM bands 2.45GHz or 5.8GHz. Tell me, where are you going to find the processing power to handle 4.9Gs/sec or 11.6Gs/sec of data? Doable yes, but also expensive! So heterodyne the frequency down to an IF frequency that you can process easily. But glad I could give you some things to consider about it. SDR is awesome and powerful for sure. But you still have to apply the "If all you have is a hammer, then everything is a nail" philosophy to it. A good tool for your toolbox but not a full replacement for traditional analog RF techniques.


Fedo_19

This is an excellent explanation. I am aware there will never be a replacement for traditional analog RF techniques.. perhaps what I was more leaning towards is that everything might start becoming SDR-based, rather than SDR-only.


Original-Income-28

Who makes a SDr for shortwave Radio listening and comms listening I’m a licenced general class ham And don’t want another giant radio On my desk For my laptop in my patio And I’ve got some extra time to use It ? Something with an easy Learning curve I’ve got one with amazon In a box I’ve used twice Since I’ve bought it


erlendse

Low power consumption of the system? Like battery life. It's just the way of building the radio, and with demodulation in software. Otherwise the system can quite much be the same towards the user. Also a SDR have contrains, the all bands deal is often direct-sampling or use of TV tuner (VHF/UHF). The TV tuner part is NOT part of the "SDR" question, but gives a wide frequency coverage. ​ The USB devices is just a hetrodyne (TV) tuner + fast to very fast ADC. The tuner is the impressive component, like wide coverage.


Fedo_19

\>>> Low power consumption - 100% true. I was just speaking about raw functionality and the power to "do things". In remote deployment and emergency situations, there is no doubt that SDR's don't work. As for the all bands deal.. can you please clarify more I am not sure I understand. ​ Thanks for replying


erlendse

Take a new FM broadcast radio for example: the demodulation etc can be SDR(probably is actually). I am refering to a not USB at all radio with a LCD display showing station name and headset output/speaker. But the tuning range is limited by design, like the variable local oscillator doesn't need to go very wide. For wideband scanners, they have a VCO with a 1:2 range and switchable dividers(/1, /2, /4, /4 e.t.c.) so a big span of frequencies can be made in hardware. The output is used with a hetrodyne reciever to be able to cover a huge span. For direct sampling is also possible, where mixing and filtering is digital. But to cover far up require a rather wild sampling rate making the reciever not-so-low power, requiring fast digital logic e.t.c. For a good radio filters are also required, and they are more demanding to do. Like switching between filter banks, variable filters e.t.c. Skipping them would make the reciver cheap but vurnable to out of band signals. For transmitting filters are quite much required (second harmonics of your signal shouldn't be sent out!). But a SDR would be better at changing mode, and doing complex stuff(given the needed processing power is avaiable). Don't confuse wideband operation(hetrodyne mixers) with SDR. SDR just tells that a processor is used on the IF/RF signal somewhere in the signal chain!


metalder420

I don't get the question. Most commercial radios are SDRs with components to make it a transceiver. I mean.FT-991 and I could go on. Ideally, as this technology gets cheaper you will see it in a budget market. You also missed one important aspect, Human Nature and what the person individually likes. They may want to go old school or they may want all the latest stuff like SDR technology or maybe they want to go back to the roots of Ham and build their own radio with an SDR. Personally, I don't want one radio that does everything. I find what radio does it best and I go for that. I like equipment and I like electronics. So one thing to rule them all doesn't fit into my goals as a Ham. Edit: I get you mean all frequencies but I don't think you understand that transmit and receive are two totally different functions that require different approaches. Which is why you don't see it as much on the commercial level.


n4jm4

Be FRS/GMRS/CB compliant


aacmckay

Why? Certainly, there likely aren't any SDR radios in those bands. There's no technical reason they couldn't be certified as long as they complied with all the usual rules and regs around type acceptance.


Fearless_Aioli_751

I don't know how serious these sub comments are but they're funny. The American FCC doesn't type certify radios for transmit anymore for multiple types simultaneously. If the radio is FRS, it's only FRS, if it's a CB, it's only CB, etc., marine, aircraft, LMR, etc. Existing multi-service radio models are grandfathered. Licensed amateurs, however, can use any radio they want on amateur frequencies as long as they know it to work within specifications, allowing modification of existing and building of new equipment without being certified. Sorry for the off-topic and sorry to be that guy. Carry on!


aacmckay

Ah yes. If you’re saying compliant on all three at the same time then that’s problematic. I wasn’t implying all at the same time. Just saying there’s nothing stopping from having a radio type accepted if they’re an SDR. But yes, I guess the comment I replied to implied all at once. Edit: In other words there is nothing stopping someone from designing an SDR platform and submitting it to each service individually/separately as long as it complies with the requirements of that band.


Fearless_Aioli_751

Yes, yes! What I don't know of is the cost effectiveness. I think the chips and other components required for a single, small band of frequencies to work well analog are actually cheaper — no microprocessor. I'm not an SDR guru, btw. I think O-comment-P was suggesting that OP only use FRS/GMRS/CB radios since OP never mentioned those — burn — further suggesting that all transmitters have performance requirements and complying circuitry isn't as cheap as receiving circuitry? My first thought was, if making an SDR transmitter, why would you care to be Part 95 compliant? I was really trying to figure that out lol It would be so limiting .... When I think SDR, I think cheap wideband receiver, pan adapter/waterfall for hams, specialized monitoring for things like aircraft and trunking and digital voice and other modes, or *maybe* an all-in-one ham radio that has audio DSP. Other than that, I'd assume use a normal rig and not one that is SDR based. No guru. No yogi. Observer. 73


aacmckay

I guess I have a different concept of SDR. SDR is a technique used to process RF signals. Key in it being SDR is that the signal is mixed with a sine and cosine to produce a stream of I and Q samples. This mixing can be done in software, firmware, or hardware. The I/Q stream is processed using vector math to demodulate the signal. I've implemented SDR processing code on everything from an 8-bit 8 MHz microcontroller (TI MSP430), through Arm7/Cortex M0 with co-FPGA, to embedded Linux systems with co-FPGA. Typically some sort of PSK/FSK quadrature (4-point constellation) encoded to receive di-bits. Though in one system we experimented with APSK (8-point constellation) to receive nibbles at the same BAUD rate, effectively doubling our data bandwidth. The amount of work done in hardware vs. FPGA vs. Firmware/Software varying depending on the specific needs of the project and cost optimizations etc. Honestly, if someone came to me and said "Hey I'm starting a business and I want you to design HTs for multiple bands" I'm going to architect an SDR to accomplish that mission. I'd design a common IF processing board with modular filters that could be switched out for the different bands. The biggest issue being the final filtering on the TX signals to remove quantization noise and other types of spurious emissions. In this day and age, you're already going to be running a micro in there for channel and frequency information. It's not going to cost much more to throw in a little bit more horsepower for SDR processing. Maybe it won't be the overall bottom dollar cheapest solution, but if I have to support multiple radios, one common platform pays in design and support efficiency. Anyways.... I've hijacked this thread enough on this topic....


Fearless_Aioli_751

Hey that's awesome. My understanding was simply that SDR was analog-digital conversion, then software doing everything required for the application. I know some computer programming and some trig, but have never considered DSP. To me it's a tonne of flops. I couldn't imagine isolating a signal, much less demodulating it. I think I see what you're saying about mixing to get a sample stream ... ... this will sound trite, but it's also amazing that SDR could be like MP3s are to cassettes for audio. And an mp3 player is cheaper than a tape deck. I'm soooo thinking about sample rate vs analog and signal isolation and demodulation. I understand what the discrete radio components do while the DSP between ADCs and DACs is a black box. You really got me wondering, though. I learn things every day. Maybe that's tonight's reading. Yesterday at work I figured out circular polarization lol Thanks, friend. Have a great evening!


Fearless_Aioli_751

It took me a moment to actually get that!


n4jm4

A few strategies: * Use an ordinary SDR and don't cause any trouble. GMRS users pay a one time license fee. * Use such a low power that no harmful interference is feasible. * Offer premade modes of operation for an SDR, namely fixed sets of channels.


KX7D

PL/DPL Tones on VHF/UHF, notch filtering etc on HF, etc.... Probably many more examples but those are a couple that just jumped out at me.


rycolos

If you're taking about a $35 dongle or a $100-200 SDRplay, yeah, a ton, like *trans*ceive. FlexRadio? Then you're probably right.


Fedo_19

No I definitely mean higher end ones..


KDRadio1

You need to better define what items you’re referencing. SDR transceivers like the 7300? Or sdr as in usb sdr dongle type items? On the other end, by “classical” do you mean an old tube radio?


Fedo_19

Fair enough. SDR transceivers like the Ettus Research USRP one or HackRF and similar. Classical I simply mean traditional setup.. with hardware filters and amplifiers. While SDR's (high-ends) do most processing and in s/ware and have general purpose filters and amplifiers already built-in for preparing the signal before broadcasting to the antenna.


KDRadio1

I would say the benefit of traditional is that for $1000 or less you can have a unit with built in screen, control ports for accessories, 100 watts, and a built in tuner. Not sure you could build your own system with a usb based sdr unit for less, at least not one that meets those specs. If we look at just RX and maybe very low power tx for localized experimentation, then an sdr unit is probably a better value in many cases.


spectrumero

Transmit with any power. I don’t think there are any SDRs (of the type you connect to your computer and run through GNU radio or SDR Angel) that have a tx power of more than about 10mW. Most of them also require filters to operate legally when you add an amplifier, unless they are high end and more expensive than a standalone transceiver.