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Author Topic: SDR - where to start from?  (Read 517 times)

IC8CYV

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SDR - where to start from?
« on: October 07, 2022, 09:54:02 AM »

My QTH doesn't really allow much space for antennas nor has the greatest horizon, I am in fact gonna arrange a long wire to try and at least listen to some HF with my maiden FT897D, I have also been wondering how does it work with an SDR dongle to listen to, say, from HF to V-UHF with all that is in between, of course no limitation to bandwidths but just wondering, with my gear (Yaesu FT897D and Apple Mac computer), if there is some solution to at least listen to some communications to revive the radio passion.

Grazie
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N2DTS

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Re: SDR - where to start from?
« Reply #1 on: October 07, 2022, 10:28:49 AM »

Most dongles and radios like the airspy hf plus or sdrplay are over sensitive on HF.
A long wire should be good for HF.
An RX loop antenna is also good and very small, can even be indoors and you can even make one yourself and buy one of the balanced preamps on ebay for about $10.00.
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G8FXC

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Re: SDR - where to start from?
« Reply #2 on: October 07, 2022, 10:46:15 AM »

The cheap SDR dongles can produce surprisingly good results, but they can be difficult to set up. They are being used out of context - often originally designed as DVB-T receivers - and the configuration routines can be complicated.

If your budget will run to it, then get an SDRPlay RSP1A - it will perform well and configuration is easy.

Martin (G8FXC)
« Last Edit: October 07, 2022, 10:49:17 AM by G8FXC »
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KE8UVC

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Re: SDR - where to start from?
« Reply #3 on: October 07, 2022, 11:14:15 AM »

Giovanni,  have you looked at a 'loop on ground' antenna?   If your main focus is to have a decent 'receive' antenna, it might be worth a shot.  If you have enough room to make a square at least 4.6 meters on each side, you might be surprised at the results.  KK5JY has an excellent write up here:
www.kk5jy.net/LoG/

It will not perform well as a transmit antenna, but works great as a strictly receive antenna, and it's fairly easy to build.
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WY4J

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Re: SDR - where to start from?
« Reply #4 on: October 07, 2022, 02:54:07 PM »

I have had an SDRPlay RSP1A for the last 6 years and is done a great job. Connected it to my Kenwood TS-590SG so now I can control the rig via the SDR. I'm sure there are others good ones around, I just happened to purchase this one.
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N1IG

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Re: SDR - where to start from?
« Reply #5 on: October 07, 2022, 02:56:13 PM »

Have you tried other people’s sdr’s ?

http://kiwisdr.com/public/
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KE6SLS

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Re: SDR - where to start from?
« Reply #6 on: October 07, 2022, 04:23:28 PM »

..  gonna arrange a long wire to try and at least listen to some HF with my maiden FT897D . .

Grazie

Most folks say long wire (at least 2~ for band of interest) but typically mean RANDOM WIRE.  And, with either type of antenna you have a great "transmitting antenna."  Just need to create a counterpoise and you are in business!  I hope you DO decide to get on the air with it--the bands are GREAT right now!

73
j
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AK4YA

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Re: SDR - where to start from?
« Reply #7 on: October 18, 2022, 06:46:55 AM »

I wish someone could "categorize" all the different SDR technologies out there.

Ive seen these terms thrown around:
  • DDC/DUC
    direct sampling
    quadrature
    I/Q

Id like to understand how each one works differently.
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N2DTS

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Re: SDR - where to start from?
« Reply #8 on: October 18, 2022, 05:53:51 PM »

There is a lot of good info on sdr on line.
All the methods can work very well, the devel is in the details.
Direct sampling generaly means the rf is sent to a A/D converter and digitized and then processed.
It has the advantage of being able to look at and listen to multi bands at the same time, like 160 40 and 10 meters at the same time.
Or, to improve performance it can go through a band pass filter.
The Anan and Flex radios (and the new K4 from Elecraft do this.
The Elad fdm duo did it also, along with the QS1R and the Persious.
The number of bits in a sample, 12, 14, 16 improves the dynamic range as you go up in bits.

Then there is downconverted, the RF is mixed down to something like 8 MHz, put into a filter and then digitized and processed. The new FTdx 101 and 10 do that.

The original method was to downconvert rf to audio, digitize it into I and Q and then process it.
That method can still work quite well.
The Flex 3000 and 5000 did that, and many other radios.

There seems to be two ways to get very good close strong signal rejection, digitizing into more bits or filtering out the strong unwanted signals by downconverting and using a good analog filter to limit what gets to the A/D converter.
A lower frequency (8 MHz) can also use a cheaper A/D converter with more bits.
From what I understand, you have to sample the highest frequency you want to process at least 2X that frequency, so at 60 MHz you need to sample at at least 120 MHz.

All the above may be right, or sort of, just what I get from reading stuff since SDR came out.
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AI5BC

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Re: SDR - where to start from?
« Reply #9 on: October 19, 2022, 08:40:08 AM »

Try one of the discone scanner antennas.
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AK4YA

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Re: SDR - where to start from?
« Reply #10 on: October 22, 2022, 06:01:05 AM »

How much delay is there in rx audio or a true sdr versus a superhet?  The question is related to decoding the very fast digital modes in time to respond within a matter of a second or so.   Even with a superhet it is sometimes difficult
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G8FXC

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Re: SDR - where to start from?
« Reply #11 on: October 22, 2022, 08:14:19 AM »

How much delay is there in rx audio or a true sdr versus a superhet?  The question is related to decoding the very fast digital modes in time to respond within a matter of a second or so.   Even with a superhet it is sometimes difficult

There certainly can be a noticeable latency - and it is not necessarily a question of SDR vs. superhet. I run an SDRPlay RSP1A as my high resolution panadaptor with a Yaesu FTdx101D as my HF transceiver. Both are SDRs and neither is a direct sampling SDR. There is a noticeable delay between the two - with the RSP1A coming second. I don't have the equipment necessary to measure it accurately, but I would guess that it is of the order of half a second. It is sufficient to be annoying if I have the two tuned to the same signal and the volume turned up on both...

Martin (G8FXC)
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N2DTS

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Re: SDR - where to start from?
« Reply #12 on: October 22, 2022, 01:42:41 PM »

All the USB based receivers have a lot of latency, its built in the USB port.
3.0 may be better but no radios use that yet that I know of.
Firewire and Ethernet are much better, then it comes down to the computer and settings like buffer size and sample speeds.
Some radios that use an FPGA also have some latency, others are quite good.
An analog receiver will be lowest.
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N3KXZ

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Re: SDR - where to start from?
« Reply #13 on: October 31, 2022, 10:13:02 AM »

@N2DTS: can you give examples of any analog based SDR receivers? Or any Ethernet based SDR receivers? Or am I misinterpreting your statement?
« Last Edit: October 31, 2022, 10:17:26 AM by N3KXZ »
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N6YWU

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Re: SDR - where to start from?
« Reply #14 on: October 31, 2022, 12:24:11 PM »

... examples .. any Ethernet based SDR receivers?

Newer Flex radios, Apache Anan's, and Hermes Lite 2's are examples of Ethernet based SDR's.  I have a HL2, and the latency via ethernet thru an iPad SDR is very low, milliseconds.  Whereas the latency from an RTL-SDR via USB thru a PC seems to be around half a second or more.  Big difference.

Most any receiver made 35 or more years ago is purely analog, as signal processors weren't fast enough back then to run inline in either the RF or audio signal paths.  My 757GX-II only used its microprocessor and software to control the front panel IO.
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