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Author Topic: SDR receiver basic questions  (Read 9562 times)

Offline ChrisSmolinski

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Re: SDR receiver basic questions
« Reply #15 on: March 01, 2018, 2200 UTC »
Lol, if you have a 340 and wj1000 you already have sdr rigs. Stand alone sdr rigs like perseus, afredri, rsp just lack the gui and controls that are in hardware with the 340 and 1000, the pc screen and kb/mouse make up for for the lack of a display and tuning knob. Isn't there a IF output on both the 340 and 1000? All you'd have to do is feed that IF signal to a cheap rtl dongle and use most any sdr app to see (as well as hear via vrx) what is in the IF stream of those fine rigs. Also you'd be hard pressed to find a inexpensive sdr that is anywhere near the performance levels of the 340 and 1000.

The 340 and WJ1000 are good radios and use DSP (a la the NRD-545), but are not SDRs.  Many radios have an IF output (even my ancient R-71A has one) but that doesn't make it an SDR. In fact, having an IF output pretty much confirms a particular radio isn't an SDR, at least not a DDC SDR  :P
Chris Smolinski
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Offline Traveling Wave

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Re: SDR receiver basic questions
« Reply #16 on: March 02, 2018, 2101 UTC »
Josh has a good point. I have a Kenwood TS480 and I use a cheap RTL Dongle that is fed by the 1st IF stage of the TS480. The dongle is then connected to the laptop RS232 port. I run HDSRD software for the SDR display and use Omni-rig for rig (interface) control software. Both Omni-rig  and HDSDR are free. Omni-rig supports the following transceivers and radios....

•TS-440, TS-480, TS-570, TS-590, TS-690, TS-850, TS-870, TS-930, TS-2000, all other Kenwoods
•FT-100D, FT-450, FT-747, FT-757, FT-817, FT-840, FT-847, FT-857, FT-897, FT-900, FT-920, FT-950, FT-990, FT-991, FT-1000, FT-1000MP, FT-2000, FT-9000, FTDX-3000, FT-DX5000MP
•IC-78, IC-275H, IC-703, IC-706MKII, IC-706MKiiG, IC-718, IC-725, IC-726, IC-728, IC-735, IC-737, IC-738, IC-746, IC-746Pro, IC-751,IC-756, IC-756Pro, IC-756ProII, IC-756ProIII, IC-761, IC-765, IC-775, IC-781, IC-821, IC-910, IC-970D, IC-7000, IC-7100, IC-7200, IC-7300, IC-7315, IC-7410, IC-7600, IC-7610, IC-7700, IC-7800, IC-7850, IC-7851, IC-9100, IC-R75, IC-R8500, IC-R9000, IC-M70
•CODAN, Elecraft K2, Elecraft K3, Ten-Tec Eagle, Ten-Tec Paragon II, Ten-Tec Orion, Ten-Tec Jupiter, Ten-Tec Omni VI+, Ten-Tec Omni VII, TenTec RX-350, JST-245, DX-77, NRD-535(DG), PowerSDR, Perseus, FRG-100, ZS-1, Elad-FDMSW2, ADT-200A, AOR AR5000, AOR AR8600, SmartSDR

Lastly, you may not need to tap the IF stage if your radio has a receive out and a receive in. Check you-tube to find this method of hook up.
 

 
« Last Edit: March 02, 2018, 2128 UTC by Traveling Wave »
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Offline fpeconsultant

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Re: SDR receiver basic questions
« Reply #17 on: March 02, 2018, 2126 UTC »
You guys (?) all better be careful because if I do make the jump to an sdr, you'll be dealing with lots of probably really dumb questions from me!!
Thx again to all of you,
FPE
Near Chicago, IL USA.  Drake R8, Ten-Tec RX340, JRC NRD545, Watkins Johnson HF-1000, Wellbrook loop at 28', 43m inverted vee.  Please QSL to fpeconsultant@aol.com thanks.

Offline Josh

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Re: SDR receiver basic questions
« Reply #18 on: March 03, 2018, 2011 UTC »
You're well set for program listening/pirate hunting/dxing as is with the knob radios.
Where the bespoke sdr shines most is in digital mode decoding. I view the sdr rigs as I do the R390A, great for monitoring a specific channel or set of channels, not so great at cruising a band. Also the knob radios don't need the pc running just to function as a radio. Anyway, here's what is spread across two monitors as I compare hfdl decode performance between decoders, the sdr is an RSP2 fed with a off center fed dipole. The RSP is controlled by Console v3 and has 3 vrx in operation.
Amazing the sdr capabilities of today, and for so little money too. What used to be a room with dozens or hundreds of R390As consuming 115 watts of power each plus attendant devices and maintenance personnel is now reduced to a little black box a bit bigger than a pack of cigs costing less than $200.
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Offline ThElectriCat

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Re: SDR receiver basic questions
« Reply #19 on: March 06, 2018, 0025 UTC »
Hopefully this post isnt too long, but I feel it may be helpful

The SDR can be divided fairly cleanly into three parts
the hardware
the operational software/firmware
the user interface. 

Most of the time, the lower end (<$1k) radios combine the software and user interface, and the higher end ones typically have some of the operational parameters written in firmware (one time code on an FPGA) and do only the second half of the radio operations on the host computer (the one you plug the SDR in to.)
          The ideal SDR (the one that is truly "software defined") would perfectly digitize infinite RF spectrum with no noise, error, or limits (not possible) and do all of the radio parts there.
          The real SDR usually has some form of down conversion, and always has some form of filtering. and then the remaining parts of the reception and demodulation are done in software. 

the fundamental point of all this is that an SDR cannot have any functionality that a traditional analog radio cannot have.
All parts, filters, mixers, local oscillators, multipliers, must be implemented in software just as they must be in hardware in an analog radio. 

That being said, there are many things that are possible in software that although technically possible in real hardware, are not practical, a 100 pole filter, fft, or fully adjustable equalizer for example.

so to put it briefly, no an SDR will not provide you with anything a traditional radio cannot. 

instead, what the SDR really gives you is the ability to model a "real" radio in a way that is infinitely alterable, and free from inaccuracies like component tolerance or stray capacitance.

that being said, the application that runs the SDR (of which there are probably over 1000) could be written to search the internet for whatever frequency you are tuned to and display that page in the database to give you a real time callsign readout.

P.S, I like the HackRF ONE, even though it has a poor noise figure, it can transmit as well as receive, and makes for quite a piece of budget test equipment.
In another life, I could have been a telephone engineer.

Offline Token

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Re: SDR receiver basic questions
« Reply #20 on: March 06, 2018, 0049 UTC »
Many radios have an IF output (even my ancient R-71A has one) but that doesn't make it an SDR. In fact, having an IF output pretty much confirms a particular radio isn't an SDR, at least not a DDC SDR  :P

Some DDC SDRs do have an IF output.  For example the Icom R8600 has an IF output.  Above 30 MHz it downconverts, so in those bands it is not a DDC but rather a hybrid, VHF+ downcoverted to base band.  But below 30 MHz it is DDC.  I have not seen a full schematic, and so far have only seen a simplified block, so I am not sure how the radio gets filtered and tuned IF out while being DDC on 0 to 30 MHz, but that is the claim.

T!
T!
Mojave Desert, California USA

Offline ChrisSmolinski

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Re: SDR receiver basic questions
« Reply #21 on: March 06, 2018, 1215 UTC »
Some DDC SDRs do have an IF output.  For example the Icom R8600 has an IF output.  Above 30 MHz it downconverts, so in those bands it is not a DDC but rather a hybrid, VHF+ downcoverted to base band.  But below 30 MHz it is DDC.  I have not seen a full schematic, and so far have only seen a simplified block, so I am not sure how the radio gets filtered and tuned IF out while being DDC on 0 to 30 MHz, but that is the claim.
T!

I've seen some speculation that the 10.7 MHz IF for HF is regenerated from the sampled data. So it's more a "virtual" IF than "real" IF, but effectively the same from a user point of view.
Chris Smolinski
Westminster, MD
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Offline Token

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Re: SDR receiver basic questions
« Reply #22 on: March 07, 2018, 1055 UTC »
I've seen some speculation that the 10.7 MHz IF for HF is regenerated from the sampled data. So it's more a "virtual" IF than "real" IF, but effectively the same from a user point of view.

I have seen the same speculation, and I honestly do not know.  However, I think, based on the observed operation of my R8600, that this is not how it is done.

If the IF of the R8600 was regenerated sampled data you would expect that the displayed IF bandwidth would be pretty consistent, related as it is to the sampled data and the sampled data having some fixed maximum sampled width.  The maximum displayed bandwidth of the R8600 is about 5 MHz, so I would expect any regenerated IF to be a bit more than 5 MHz of width.

However what we really see is variable bandwidth on the IF that seems to be tied to the bandpass filters, and sometimes over 14 MHz in width.

Also, on HF below 6 MHz there is a definite image in the IF that is on the upper side of the IF freq (10.7 MHz) plus 2x the tuned freq, this can equal an IF bandwidth of well over 15 MHz, with half of it being an image.  If you stay +/- 3.5 MHz of the 10.7 MHz IF center freq you will never see this, and it is no issue, but if you look out wide you can see it.  Also there is a birdy/LO leakage that is always tuned freq above the IF center freq.  I suppose this could be DC if it was all regenerated sampled data.

To me the IF is acting more like some kind of mixed signal product rather than some regenerated data.  But like I said, I am not sure.  If I have time this weekend I will break out the test equipment and try and get a better hand on what it is doing where.

T!
T!
Mojave Desert, California USA

 

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