[Premium-Rx] New radio selection

Gary Geissinger ggeissinger at digitalglobe.com
Sat Jan 31 12:38:17 EST 2009 

Dear Bill,

I tend to agree with everything that you and Michael said.

Although I am a DSP user both at my job and at home (see my article in July/August 2005 QEX) I prefer to listen to receivers that use analog elements in the signal processing chain.

It's really hard to put into scientific terms, but they seem to sound better.  I've compared DSP based receivers like a K3, HF-1000, and IC-7800 with analog receivers like an R-9000, R8B, and WJ-8718A.  If you use high quality earphones (I like the Sennheiser ones too; I use HD490s) the analog receivers just sound better.

I've matched bandwidths, put both receivers on parallel taps of a multicoupler, disabled as much DSP processing as possible and the analog receivers still sound better.  Although DSP based AGC can really screw up a receiver (my WJ-8712 is impossible to listen to) that's not all there is to it. 

Since I'm not a communications engineer (I leave that level of analysis to folks like Rob Sherwood) I haven't dug into why this is true.  But I have some prime suspects:

1.  Quantization effects due to the number of effective bits in the A/D (not just bits, but effective ones).
2.  DSP algorithms are only an approximation of linear systems due to effects like a zero-order hold.
3.  For cost reasons receivers simplify the algorithms/filters to fit into lower performance DSP chips.
4.  Then there is the AGC.

Clearly the newer DSP based radios sound much better than the older ones.  This makes sense as the processors are more powerful and the A/Ds have more resolution and sample at faster rates.  Maybe without a direct comparison they sound good indeed.  But I'd still rather listen to BBC an R-9000 or WJ-8718A than an IC-7800 or K3.

A while ago I decided to put the "tubes vs transistors" argument to the test.  I designed and built a stereo amp out of both technologies.  Well, the transistor amp measures better in every regard.  But the tube amp sounds better.  One argument for this is that tubes tend to generate harmonic distortion due to their quadratic term in the transfer function.  Transistors, on the other hand, have an exponential term in theirs.  That makes the distortion more annoying.  Another argument is that the harmonic distortion "fills in" the harmonic sequence of music, so it sounds richer.  

I suspect the difference between DSP based and analog based receivers is a little more complicated.

BTW:  I try to turn off every digital device that I can in the house while I listen to SW.  Every one of them, including the little switching power converters, generates a little noise somewhere in HF.  I wish my neighbors would occasionally turn off all their noise-makers as well.

73's,

Gary WA0SPM 

-----Original Message-----
From: premium-rx-bounces at mailman.qth.net [mailto:premium-rx-bounces at mailman.qth.net] On Behalf Of Bill Mason
Sent: Saturday, January 31, 2009 09:59
To: 'Michael O'Beirne'; 'PREMIUM-RX'
Subject: Re: [Premium-Rx] New radio selection

Dear Michael:

Well put and spoken like a true Irishman! I certainly agree with your
analysis. I mainly use Collins, Racal and Harris receivers of various
nomenclatures though I have numerous other receivers.  

When I first had visual contact with a WJ receiver of the series about which
you opine, I also felt it to appear flimsy, a fact proven upon lifting the
receiver expecting it to be heavier and almost losing control and dropping
it!  After that and upon further inspection both internally and externally,
I have never coveted a WJ device.

I was employed by Collins (Dallas, Texas) in the '60s and having served on a
couple of their quality control committees (an adjunct to your normal
responsibility) I became aware of a design and construction philosophy that
no manufacturer or designer has surpassed before or since.  I cannot view
other equipments without using that philosophy as a basis of comparison!

Enough of my chatter....Outstanding analysis and enjoyed the read.

Bill Mason
W5STP   

 

-----Original Message-----
From: premium-rx-bounces at mailman.qth.net
[mailto:premium-rx-bounces at mailman.qth.net] On Behalf Of Michael O'Beirne
Sent: Saturday, January 31, 2009 8:27 AM
To: PREMIUM-RX
Subject: [Premium-Rx] New radio selection


----- Original Message ----- 
From: "Michael O'Beirne" <michaelob666 at ntlworld.com>
To: "Shane White" <shanewh at gmail.com>
Sent: Saturday, January 31, 2009 2:14 PM
Subject: Re: [Premium-Rx] New radio selection


> Dear Shane
>
> I read your email today chuckling and with a high element of sympathy. 
> Put simply we both want the same things and we are both crying for the 
> moon because no single receiver exists that I know of that encompasses all

> of your desiderata.
>
> I have never used a K3.  The review in the RSGB's RadCom last year by 
> Peter Hart (a highly respected engineer and reviewer) sang its praises. 
> Other users have done the same.  But, I query, what have been the 
> comparable standards of comparison?  If it's other ham gear, then that is 
> frankly not a big deal.  I have used some of industry's best and I reckon 
> my ears and fingers know a good set or two.  Once you have used commercial

> and military radios made by the likes of Racal, Redifon, Plessey, Skanti, 
> Marconi, Dansk Radio, Collins, Siemens and Rohde & Schwarz, all made for 
> the high end of the professional market, the likes of Icom, Kenwood and 
> Yaesu pale significantly, though in fairness the very latest offerings 
> from Icom have been a great improvement.
>
> Great claims are made for "digital" but you should never forget the tale 
> of the "Emperor's new clothes".
>
> Digital Audio Broadcasting ("DAB") is supposed to be the bees' knees for 
> hifi broadcasting and in UK will almost certainly replace Band 2 FM in a 
> few years time.  However, several commercial reviews have commented that 
> the data stream is heavily compressed in order to cram umpteen dozen radio

> stations into the limited bandwith and that DAB is basically an MP3 
> standard.  That's great for trannie radios and MP3s but it does not stand 
> critical comparison with good quality analogue FM.  Everyone with sensible

> technical knowledge accepts that given current standards, the BBC would 
> not have selected DAB today, but we are stuck with what is already a 
> legacy digital system.
>
> Similar claims are made on HF for "digital".  Certainly the technical 
> specs of selectivity achieved by digitising the IF and AGC look 
> impressive.  But in my view the specs are merely the starting point.  The 
> real test is the impression of the sound in your ears.  After all what 
> earthy use has a radio unless to deliver quality audio to your ears?
>
> This said, most modern radios are not really designed for human operators.

> Most are under computer control and are listened to by computers owned by 
> the security services for the usual unfortunate reasons or for data links 
> for the commercial and military.  Human operators are far too expensive to

> keep on the payroll!
>
> I do the usual critical technical tests but my ultimate test is to listen 
> carefully on good quality Sony or Senheisser headphones to a station that 
> I know well, typically the BBC on 198 kHz and on 15,400 MHz.  Any trace of

> hum is a big minus issue.  Any trace of microprocessor squeaks and bumps 
> is an even bigger minus.
>
> Any objectionable coloration is no good either.  Most of that will be 
> caused by phase distortion in crystal filters or mechanical filters.  The 
> true perfectionist will seek fully phase-compensated crystal filters. 
> These can be very expensive.  They were used mainly for receiving fast 
> data on HF where phase distortion across the passband will completely muck

> up the relative timing of the data pulses and may well render the signal 
> unprintable.  I acquired a matched pair for my Marconi H2540 receiver for 
> the princely sum of £10 at a flea market.  The factory list price from 
> Marconi was £350 for the USB filter and £1,200 for the LSB filter plus 
> postage plus VAT in the mid 1980s.  They improved the sound quality no 
> end.
>
> Many amateur receivers and transceivers attempt to achieve better 
> selectivity on SSB by using narrow SSB filters of 2.4 kHz bandwidth or 
> even less.  Under conditions of strong adjacent interference they are 
> useful but the resulting boxy sound of the human voice (to me) more 
> resembles a cat being castrated.
>
> If you are going to listen to music or the human voice using SSB mode 
> (useful when there is lots of QRM) you need to use better professional 
> filters with a bandwidth of at least 2.7 kHz.  The SSB filters on my Racal

> RA1792 have a bandwidth of 2.9 kHz and sound very good.
>
> Great claims are made for using synchronous AM detectors.  A few work 
> really well but they are complicated and expensive.  The simple designs 
> are OK but often not much better than a traditional diode detector.  I am 
> told that the Sherwood "add on" detector unit is excellent.  I use a 
> fairly similar "one-off" professional design made by Surrey Electronics, 
> but they had to stop selling under threat of patent infringement from 
> another company called PhaseTrack.  The latter marketed a superb HF 
> receiver specifically designed for commercial rebroadcasting called the 
> "F1-2".  The IF selectivity was formed not by filters but by a complicated

> phasing system.  The result was total lack of any phase distortion, a flat

> audio bandwidth from 50 Hz to about 4.5 kHz and a total harmonic 
> distortion under 0.5% across the whole of that bandwidth.  I have one and 
> wow it is incredible.  I have yet to meet any DSP that will match that. 
> It will come in a few years but as far as I am aware not at present.
>
> Diode AM detectors are regarded as terribly old fashioned but that is 
> mainly because some listeners don't know any better.  The very best diode 
> detector is on the ancient GEC BRT400E of the 1950s.  The recovered audio 
> quality is staggering.  This is not just me.  I quote a well known hifi 
> reviewer and ham, the late Angus McKenzie G3OSS with whom I had many an 
> exchange of views.  These sets were used extensively for monitoring by the

> BBC, and BBC engineers demanded the highest professional standards.  Alas 
> the remaining ones are pretty bashed up and will need a great deal of 
> renovation.  They are also very big, hot and heavy.
>
> The venerated RCA AR88D still has an excellent reputation for AM quality 
> with several selectable bandwidths and will hold its own up to 10 MHz but 
> the selectivity is poor by modern standards, it weighs 100 lbs and will 
> almost certainly need realignment.  No one would really want to use one 
> for SSB.  The build quality however is superb and these radios originally 
> cost a fortune.
>
> The valved Collins gear such as the R390 and 51J-4 are mechanically 
> gorgeous and were even more expensive.  You won't find better construction

> anywhere. They are heavy to tune (dozens of gears and moving slug racks 
> inside) and the recovered audio is not so good.  But they are fun to use 
> if you like big panels, big meters and decent sized meters (as I do).  An 
> R390 plus the Sherwood synchro detector unit is said to be superb.
>
> In similar vein, the Racal RA17L is a nice old valved receiver but the 
> audio is only OK, not outstanding, and they all need restoration after 40 
> years +. However, their usefulness (and audio quality) increases mightily 
> when married up with an external SSB adaptor such as the RA121 or RA298, a

> VLF converter such as the RA137 (listening down to 12kHz), a digital 
> display adaptor (displays to 10Hz) and a bargraph tuning adaptor (displays

> to 10Hz). But you are then looking at a pile of gear 19 inches wide and 
> about 22 inches high.  Mind you it will impress all your visitors !!!
>
> Most (if not all) the valves are easily available, in contrast with 
> numerous ICs.  Repairs do not demand watchmaker skills except if you have 
> to sort out the complex mechanics of the tuning drive of the R390.
>
> WJ sets are of superb construction and look handsome but many are getting 
> on in years.  Some parts may be difficult to source.
>
> My ultimate advice is to get either the newer Racal RA1772 (of the 
> mid-late 1970s (but only if in good condition) or the much newer RA3701. 
> You are assured of excellent built quality, a bomb-proof front end, decent

> IF filters, 8kHz AM filter, superb velvety tuning feel with light finger 
> tip control and are generally nice to use.  They have no unobtainable ICs 
> or other parts.  The 1772 uses a low distortion AM detector based on a 
> constant current circuit.  The 3701 uses a synchro AM detector.  Both have

> IF outputs for external adaptors.  The frequency display in both is to 
> 10Hz and stability can be measured in fractions of a Hz per week.  Neither

> has IF shift or a notch filter.  Few professional receivers until the 
> latest bunch of DSP rigs have these since such functions can be 
> implemented at little or no extra cost within the mathematics of the DSP.
>
> Two other sought-after radios with excellent audio are the Plessey PR2250 
> and 2280.  However, there are few around and many of the Plessey-made ICs 
> inside them have not been manufactured for many years.
>
> I was not impressed with the 340.  The tuning is awful compared with the 
> Racals and in the UK their cost is huge.  Others swear by them.  You need 
> to try one out and see if you can live with the tuning.  The knobs and 
> displays are good.
>
> The current "must have" is the WJ 8711A.  I tried out the original version

> at an exhibition when they first came out and was horrified at how 
> mechanically flimsy it was, the cheapness of the knobs and meter and the 
> number of spurious noises I could hear.  This view was echoed in a 
> detailed technical review in SWM where many unkind (but accurate) words 
> were voiced. The new A version is said to be a lot better but is just as 
> flimsy.  I prefer more mechanically robust rigs. I commend the words of 
> Julius Caesar (if you remember your Shakespeare): "Let me have men about 
> me that are fat............Yond Cassius has a lean and hungry look".
>
> Your needs may also be met by the Rohde & Schwarz EK085 but big, big 
> money, rare even on eBay, and repair bills ........... more big money!
>
> I hope this helps.
>
> Regards
> Michael O'Beirne
> G8MOB
>
>
>
>
>
> ----- Original Message ----- 
> From: "Shane White" <shanewh at gmail.com>
> To: <premium-rx at mailman.qth.net>
> Sent: Saturday, January 31, 2009 2:26 AM
> Subject: [Premium-Rx] New radio selection
>
>
>> Hi Group,
>>
>> I'm after advice for the selection of an HF radio receiver (or
>> transceiver) please. I currently own an Elecraft K3 but the audio is
>> terrible, especially on AM. Despite discussing this matter with the
>> manufacturer, it seems modifications to improve this aspect of this
>> radio are some way off, if at all. The problem seems to me to be
>> caused by the AGC (which can be disabled) resulting in over emphasis
>> in voice of received Bs, Ks, Ts etc. In addition, the audio generally
>> sounds "odd" for want of a better description and nowhere near as
>> pleasant to listen to as my Kenwood R2000.
>>
>> Now I'm selling the K3 and am undecided about what to buy next. Here
>> are my requirements -
>> 1. 500KHz to 30MHz coverage at least
>> 2. Capable of an AM audio bandwidth of at least 5KHz (ie 10KHz IF
>> bandwidth)
>> 3. SSB, AM
>> 4. Tuning resolution of less than or equal to 10Hz
>> 5. Preferably have an internal PSU capable of 240V/50Hz operation
>> 6. Preferably capable of S-AM reception
>> 7. Preferably include IF shift, width and notch
>>
>> I've thought of the following options -
>> 1. An Icom IC-7700. I haven't heard one in person, nor can I since I'm
>> in South Australia where shops (all two) don't stock radios.
>> 2. The soon to be released Icom IC-7600
>> 3. The Ten Tec RX340
>> 4. An older radio such as the WJ-8718A
>> 5. A Collins tube radio
>>
>> Being in Australia I'm concerned about buying an older radio because
>> parts may be difficult to source. I'd probably also need to buy a CRO.
>>
>> I'd appreciate any thoughts on this matter thanks.
>>
>> Shane.
>> _______________________________________________
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>>
> 

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