high quality radio reciever for communications? - Page 1
Forum section: electronics / rf-microwave

author: coppercone2
author_rank: Super Contributor
timestamp: July 07, 2019, 06:25:10 am
content: So I understand power amplifiers, LNAs and antennas fairly well, but have little interest or knowledge in modulators/demodulators.What are some good brands/models to look at?I am guessing in terms of older equipment you will not get the types of decoding you want (i.e. if you want old military gear that is reliable).What can be covered by 'reliable' militaryish HP like boat anchors and where will that be deficient?So like you can sit down at a bench with some head phones and knobs without any computers being required. Do they have digital ones that use discrete circuits since its just audio? (i.e. big ass TTL logic card bank radios).

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 07, 2019, 10:09:00 am
content: I'm not quite sure what you are looking for. When you mention demodulation are you looking for audio demodulation like AM/FM/SSB? Most communication receivers can demodulate that. Or are you talking about digital modes like FSK and such? That is where a computer comes in, either built in to the receiver or as a separate box.

author: coppercone2
author_rank: Super Contributor
timestamp: July 07, 2019, 04:20:23 pm
content: so FSK is new enough that they don't have 80's 'dynamic signal analyzer' style boards that have 10+ cards packed with TTL logic to do the job? do you absolutely need a computer? (i.e. 80lb box)basically what would I be missing out on if I stuck with old gear?

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 07, 2019, 05:25:19 pm
content: You don't need a computer per se, FSK is older than that but I guess that you don't want to go the modem and teletype way. So no, you will not find it built-in into an 80's receiver, simply because you need a screen/paper to output the demodulated text. Having said that, I have an Icom IC-R9000 (late 80's I think) that can receive FSK but it has a built-in CRT. I'm still not sure what you are trying to ask/do, so maybe elaborate a bit more about what you are looking for?

author: coppercone2
author_rank: Super Contributor
timestamp: July 07, 2019, 06:31:09 pm
content: well most of my gear is at best early 90's besides some specials like VNA and I generally like how it is build regarding strong chassis, good wiring harness, high repairability (if your clever, save for unobtanium parts), and general robustness.I also feel like a radio should not use a damn computer because it might be useful as a emergency tool. I want it built dead simple without layers of layers of OS software etc. I have a SDR but holy fuck it was a nightmare to get running, I need a special laptop with some kind of special linux fork to interface with it (and the linux is not updated as often as other linux so basically I have a laptop that is only meant to interface with a SDR. It does not feel practical. I can't have that kind of baloney with something like a radio set. God forbid it auto updates or something by accident or I forget and then I rendered my setup inoperable. Or it gets some kind of virus.If I had the money I might go for something like a high end laptop, carefully remove all the interface features from it after programming it and then mount it together in some kind of special chassis with a SDR, but this is very expensive because 99% chance the shitty 400$ laptop will break before the SDR does.The old gear feels more 'hardened'.

author: OwO
author_rank: Super Contributor
timestamp: July 07, 2019, 07:05:33 pm
content: I don't get what you are talking about, there are countless FSK/ASK transceiver ICs that can do raw demodulation (no framing), for example the AX5043. Why would you even think about a discrete logic based implementation that will most likely not be optimal and be a pain to interface with? Just get one of those single chip transceivers, hook up a STM32 and SPI LCD, and you should be able to get the received data displayed on the LCD in a day of coding or so.

author: radiolistener
author_rank: Super Contributor
timestamp: July 07, 2019, 08:24:25 pm
content: ICOM, Yaesu, Motorola

author: KE5FX
author_rank: Super Contributor
timestamp: July 07, 2019, 08:56:38 pm
content: Don't want a computer? TheR-390Amay be for you.Clear your desk first. If you have a friend with a forklift, now's the time to get back in touch.

author: coppercone2
author_rank: Super Contributor
timestamp: July 07, 2019, 09:23:52 pm
content: Quote from: KE5FX on July 07, 2019, 08:56:38 pmthat looks nice, but how is the reception quality compared to modern equipment?good preselector, preamp noise, etc? how much less coverage am I gonna get for 80lb?

author: 0culus
author_rank: Super Contributor
timestamp: July 08, 2019, 02:38:02 am
content: If you can power it, it'll probably still work after an EMP too. I bet it needs a fairly beefy supply.:https://www.radioblvd.com/R-390A%20Rebuild.htm

author: vinlove
author_rank: Frequent Contributor
timestamp: July 11, 2019, 08:10:17 pm
content: MFJ 8100 Kit Regenerative Radio is small, light and is good fun to operate.If you want more recent one with DSP, then XHDATA is excellent.

author: coppercone2
author_rank: Super Contributor
timestamp: July 12, 2019, 03:11:14 am
content: are the modern DSP ones capable of better SNR (worse reception)?

author: vinlove
author_rank: Frequent Contributor
timestamp: July 12, 2019, 09:39:54 am
content: DSP receivers have come long way, and now they seem very good performers.But I like the tone from the classic simple receivers such as regenerative ones.

author: coppercone2
author_rank: Super Contributor
timestamp: July 12, 2019, 11:02:37 pm
content: but.. if you want to resolve a communicate, is it better?like if you had two radios approaching a receiver along the same road, which one will pick it up first understandably (voice)? (in the case of all the different modulations it can receive).Say connected to the same antenna tuned to each radio

author: vinlove
author_rank: Frequent Contributor
timestamp: July 16, 2019, 05:46:53 pm
content: I suppose high spec. dsp designed modern high tech receiver would suit better for more demanding situations for speed of tuning, freq accuracy, stability, sensitivity, selcetivity, performance and ease of tuning etc etc.But I was talking about plain home based hobby SWLer like me, and it is good fun to operate classic traditional style regenerative radio like MFK 8100, or newish cheap portable DSP radio like XHDATA. They do everything I want. I don't need anything more fancy.It depends on what your requirement is really.

author: chris_leyson
author_rank: Super Contributor
timestamp: July 16, 2019, 06:28:27 pm
content: QuoteThe Rockwell Collins HF-2050 could arguably be described as big ass TTL logic card bank radio. It was one of the first, if not the very first DSP receiver. IMD performance is not very good and it runs very hot. Harris RF-590 is a much better receiver and if you're lucky you can pick one up with a preselector. Toronto Surplus probably have both in stock.

author: Lord of nothing
author_rank: Super Contributor
timestamp: July 30, 2019, 05:37:39 pm
content: Hmm how to use that old stuff?When I look at the Hand Radio who is use by the Austrian Military:https://www.bundesheer.at/waffen/waf_fue_tff-41-0.shtmlthere is quite no input for anything.So there must be some kind of software to controll ist who is maybe not available and without there is a low chance to program it.

author: coppercone2
author_rank: Super Contributor
timestamp: July 30, 2019, 09:58:48 pm
content: Quote from: chris_leyson on July 16, 2019, 06:28:27 pmis it a consequence of phase noise from the discrete gates?

author: fourfathom
author_rank: Super Contributor
timestamp: August 15, 2019, 01:31:08 am
content: Quote from: coppercone2 on July 12, 2019, 11:02:37 pmWe're talking about HF radio (3-30 MHz) right?If so, atmospheric background noise dominates the spectrum, and virtually any radio -- modern or old -- will pick up a voice signal equally well. They are all sufficiently sensitive, since the atmospheric noise essentially provides the noise floor, not the radio. Where you will find differences is in the filtering and dynamic range, which can make a big difference when dealing with strong off-frequency interfering signals. More modern features have fancy noise-reduction (digital filters, tunable passbands, noise-blankers) that can make a weak or interfered signal more readable.Digital signals are a bit more complicated, but generally the radio is not the weak link.At VHF frequencies the atmospheric noise issues are not so pronounced, but I would definitely want a modern receiver, rather than a boat-anchor.If you are looking for "reliability" in the face of EMP, the I guess you're stuck with tube gear, or storing your solid-state gear in a Faraday cage when you're not using it.

author: coppercone2
author_rank: Super Contributor
timestamp: August 15, 2019, 02:22:16 am
content: Well, how does the digital filter response look like in comparison to a analog radio in terms of Q, Order, Fc, etc?and it can't do everything in software because of aliasing, so it must still need a preselector

author: fourfathom
author_rank: Super Contributor
timestamp: August 15, 2019, 02:53:31 am
content: Quote from: coppercone2 on August 15, 2019, 02:22:16 amIt depends on the radio design. With a full-SDR radio, there are usually pre-select bandpass filters that reduce off-frequency signals which might cross-modulate and create in-band interference. How much this is an issue depends on the dynamic range of the SDR A-D converter, among other things. Then the sampled signal is decimated, filtered, and further digitally down-converted, where it goes through more filters and digital demodulators, tailored for the characteristics of the signal of interest. These digital filters are protected from aliasing by the preceding filter stages, and can have virtually perfect filter shape (sometimes at the expense of delay.)A more traditional superhet (single or double-conversion) will have several filter stages at the IF frequency(s) and these will provide excellent rejection of signals outside the audio passband. The modern superhet radios may do digital filtering at the IF frequency, or on the audio (baseband) signal after demodulation. Again, these digital filters are designed with the earlier-stage filters in mind, so aliasing is not usually an issue.I suppose I should ask you what your goal is here. Reliability has many dimensions.

author: coppercone2
author_rank: Super Contributor
timestamp: August 15, 2019, 04:20:43 am
content: ok but if you make a overall transfer rejection function, how do they compare in terms of dB or some quantifiable numerical metric?the overall system, what does it come out to be in rejection band interference power after everything

author: vk6zgo
author_rank: Super Contributor
timestamp: August 15, 2019, 06:41:58 am
content: Looking at your original request, back in the day, far enough, "real" FSK was used, where the (baudot) telegraph signal in the form of two DC levels was presented to an FM modulator so that it transmitted one RF frequency for mark, & the other for space.This was the way it was done in the early days of FSK ----WW2, & up to around the early '50s.Landline telegraph systems in the meantime had moved to "Voice Frequency Telegraphy" (VFT) so called because it occupies the same spectrum as an audio or "voice" signal.This could be used to modulate a higher frequency carrier (using, at first, DSB, then later SSB) & combined with other such signals, either telegraph or voice, as part of a Carrier Telecommunications system, greatly increasing the capacity of physical lines.With the wider use of Independent Side Band (ISB) transmisions, VFT signals were added to those modulating the two independent sidebands, so that a system would commonly have two independent voice channels & two VFT chsnnels.The VFT decoders were usually rack mounted, dedicated units taking up about a quarter of a full sized 19" equipment rack, although the "24 channel VFT" in use on the landline at Wyndham in the far North of Western Australia back in 1967 was quite a lot smaller.The dedicated "radio" telegraph systems worked well on most of the ISB systems of the day, as the transmissions provided a "reduced carrier" normally -26dB in the day & -16dB at night, allowing the receiver to "lock" to the transmission using a very large vacuum tube PLL.This was very effective in both producing good speech quality, & allowing the VFT units to decode correctly.Around the late 1960s, my then employer bought some ISB systems in which both the Transmitter exciter & the Receiver were purported to be so stable that the carrier could be effectively "fully suppressed"(-60 to -70 dB).Alas, this was not the case, & we were forever chasing stabilty problems.Amid this turbulent era, it was decided to use one of the spare "24 channel VFT"systems as a telegraph backup on one of these HF systems.The poor old "24 Channel" didn't like it in the least, so every day we would get calls that "The Radio channel is mutilating"I don't think Hams used direct FSK at any time, using VFT from the outset.Of course, the decoding problems were not nearly as difficult for them, as they were only dealing with one channel, could receive the signal as direct FSK if they wanted to, could "zero beat" the "space" frequency, effectively turning it into "on off" keying, or have a VFT modem in the form of a couple of a number of sharply tuned audio filters, (& switched tone generators for the transmit side).The actual decoding of the Baudot code was done by Teleprinters.When ASCII came along, things changed, both Commercially & in Ham Radio.Solid State made the modem & decoding units smaller & more convenient.TTL Logic ICs made it possible to produce VFT signals from a keyboard, & display the received messages on a CRT display.( just as well for Hams, as ASCII printers were not as prevalent as the old Baudot Teletypes).As things like Commodore PET & 64, as well as Tandy TRS 80 started to appear, most of the actual "grunt" work was done by the computer, with the box between the transceiver & radio becoming pretty much "just a modem".My involvement with Radiotelegraphy (RTTY) was pretty limited ----other Hams were much more immersed in it.I have no idea what standards they are using now, although I believe there are still a few using Baudot.Most of the computer based work on Ham radio these days is of much more recent origin, & conventional RTTY is a rarity.PS. ----Looking back at your original posting, you didn't mention FSK--- that was brought up later, so my posting may not be of value.Anyway,TL/DR --- FSK has been around virtually forever, but the transmission standards & methods of decoding it have changed radically over the years.

author: fourfathom
author_rank: Super Contributor
timestamp: August 15, 2019, 07:21:46 am
content: Quote from: coppercone2 on August 15, 2019, 04:20:43 amIf you mean parameters like passband flatness, Q (passband -3dB width vs center frequency), transition band slope, stopband amplitude, the answer is "it depends". Often a digital filter will have superior performance, but perhaps the stopband attenuation at extreme frequency offsets won't be as good as an analog filter. Or it might be better. The practical answer is that the digital filter can be easily be made as good as you need it.But these filter characteristics are only a small part of the challenge.When it comes to demodulating digital signals, there are many techniques that digital signal processing makes available. Precisely matched filters are often built using FFT techniques, where the filter characteristics are by design well-matched to the modulation characteristics. Digital signals often use multi-tone FSK, or PSK, or similar techniques, and demodulating these well with old analog methods is extremely complicated. With DSP it's easy and performs close to the theoretical limit.I suggest that you buy an SDR designed for HF such as the SDRplay-1A (https://www.sdrplay.com/rsp1a/) and see how it does for you. This may be the best $100 you can spend, and it will answer many of your questions. There are cheaper SDRs, but these only work well at VHF frequencies. If you're curious, take a look at a presentation I gave to my ham club. In it I show how I use a cheap SDR and a Raspberry Pi to make a digital receiver:http://wb6cxc.com/wp-content/uploads/2019/04/Presentation-1-0.pdfIt has examples and links to DSP tools used for filtering and demodulation.

author: coppercone2
author_rank: Super Contributor
timestamp: August 15, 2019, 07:27:47 am
content: what would an analog filter that matches the digital filter look like ?can you guesstimate the order and stuff to compare to digital filters that are implementable (for the sake of being able to imagine it)?

author: fourfathom
author_rank: Super Contributor
timestamp: August 15, 2019, 07:45:03 am
content: Quote from: coppercone2 on August 15, 2019, 07:27:47 amI'm not a DSP expert, but a reasonable FIR audio bandpass digital filter will require a few dozen taps. Here are some links that will tell you a lot:GNU Radio (a free DSP software suite):https://www.gnuradio.orgRTL-SDR (here's a big list of tools and programs):https://www.rtl-sdr.com/big-list-rtl-sdr-supported-software/csdr (a command-line suite of DSP routines that I used in my receiver project):https://github.com/simonyiszk/csdrNote that depending on what you want to do you don't *need* to build a DSP system yourself. Take a look at (for example) the Icom IC-7300 ham radio. This has a USB interface that looks like a sound card to your computer, and you can do all the demodulation with existing software. Look at wsjtx and js8call for examples.