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Old 20th May 2022, 10:25 pm   #1
sexton_mallard
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Default Reception on Shortwave

I've noticed that performance on SW always seems to be so much better on a lot of valve sets that I have worked on. Tuning indicators close up on many stations indicating a strong received signal affecting AGC more. Is there a reason why MW and LW seems inferior? the noise on MW and LW is a lot worse so perhaps the quieter noise floor and less interference is the reason.

Reception where I live in Shropshire appears fairly normal with plenty of 'mush' from digital devices and SMPS. LW is more or less unusable on sets without a ferrite rod aerial to null out some of the noise.

The few SW stations broadcasting always seem to sound quite good and not so compressed compared to those on LW or SW. Massively powerful transmitters?

My question is therefore is there something inherently better with SW overall?
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Old 21st May 2022, 12:16 am   #2
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Default Re: Reception on Shortwave

My own solution here has been to go with Internet Radios; I've just bought my 4th one. The number of stations streaming is given at anything between 25,000 and 40,000, and in among them are things as basic as Radio4 to stations specialising in very narrow and obscure topics.

I listen a lot in the middle of the night to stations in Canada and the USA, crisp and clear as R4. My original Internet Radio now feeds my Pantry Tx so I can listen to the station of my choice all over the house. My new radio has 99 station pre-sets and operates by remote control.

As far as I am concerned, this pretty much takes me back to where I started; listening to SW radio a very long time ago.

B
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Old 21st May 2022, 7:46 am   #3
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Default Re: Reception on Shortwave

the only short wave round here is cheating really, wide band web is ok, noise from smps is rife, i listened to sw a lot in the 60s but its nothing like it was.
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Old 21st May 2022, 8:17 am   #4
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Default Re: Reception on Shortwave

I think the issue here is noise. I live in fairly remote location and avoid having too many SMPS etc. Both MW and LW are excellent; better than SW. True enough that the signal level is not massive, but enough to get AGC operating and the audio is very clear. I much prefer Radio 5 Live on MW to DAB.

What is interesting, is that AM bands always sound better on a vintage set compared with a modern, usually DSP one.
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Old 21st May 2022, 8:20 am   #5
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Default Re: Reception on Shortwave

SW reception is linked to sunspot activity that influences the ionised layers of the upper atmosphere. The current cycle peaks in 2025 so things should continue to improve for a few years. However, some cycles are weaker than others and, of course, the number of stations out there worth listening to has vastly diminished compared to the 1960s. Jerry
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Old 21st May 2022, 8:28 am   #6
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Default Re: Reception on Shortwave

As far as SW listening is concerned I still consider it a challenge rather than entertainment and eschew modern methods of reception.

No doubt my opinion will change as I get ever more frustrated by poor reception but that's offset by the sheer nostalgia value of 'doing it the old way'.
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Old 21st May 2022, 1:43 pm   #7
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Default Re: Reception on Shortwave

Quote:
Originally Posted by sexton_mallard View Post
I've noticed that performance on SW always seems to be so much better on a lot of valve sets that I have worked on.
Hi,

The point everyone usually misses(including me), is that solid state bjt's produce enormous amount of transconductance(gm), when compared to a valve or jfets and, infact, I would argue that bjt's produce too much gain where radio design is concerned.

A 6d6 pentode valve gm is 1.6mA/V whereas a 2n3904 bjt produces 80mA/V.Quite simply, bjt's produce too much gain, but there are design methods to quell bjt gain and make them usable in radio design.The HRO 500 did this quite effectively.

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Old 21st May 2022, 1:58 pm   #8
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Default Re: Reception on Shortwave

Putting aside the technical problems of listening on SW now, what would you listen to? I think the modern term would be "content"; what can be found that's of interest?

I don't deny the technical challenge of RF, it's the poor rewards that diminish my interest. I still have my HRO with its 6D6's, and various other receivers, but over 50 years after my 2-valve TRF, the allure of a universe of diverse content, at the push of a button, wins out for casual listening (i.e. listening to the radio, to interesting and informative programmes, while doing other tasks).

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Old 21st May 2022, 2:16 pm   #9
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Default Re: Reception on Shortwave

Quote:
Originally Posted by sexton_mallard View Post
I've noticed that performance on SW always seems to be so much better on a lot of valve sets that I have worked on. Tuning indicators close up on many stations indicating a strong received signal affecting AGC more. Is there a reason why MW and LW seems inferior? the noise on MW and LW is a lot worse so perhaps the quieter noise floor and less interference is the reason.

Reception where I live in Shropshire appears fairly normal with plenty of 'mush' from digital devices and SMPS. LW is more or less unusable on sets without a ferrite rod aerial to null out some of the noise.

The few SW stations broadcasting always seem to sound quite good and not so compressed compared to those on LW or SW. Massively powerful transmitters?

My question is therefore is there something inherently better with SW overall?
An interesting point, but there is no specific reason why valve radios are better or worse than equivalent transistor radios on any bands. I've used both in an amateur and professional capacity. A good transistor set is better than a bad valve set and a good valve set is better than a bad transistor set!

It also depends what you are comparing. Are you working on domestic quality 1940s/50s sets or good amateur or professional communications valve radios? A modern solid-state communications receiver will (at last!) knock spots off even a good valve communications set - which of course have not evolved now for about 50 years.

Perhaps one thing to bear in mind these days is that valve radios are usually connected to the mains and this is a significant source of noise.

The type of antenna is important too. Portable transistor sets (is it these you are comparing?) have a telescopic whip which limits signal pick-up, and adding too much extra wire causes them to overload.

Up until the 1990s even reasonable quality solid-state receivers were not as good in some respects as valve sets. Poor dynamic range, reciprocal mixing being the main problems.

The radio guru Pat Hawker wrote in Radio Communication at about this time that solid-state communications receivers had only just reached the performance valve radios had reached in 1950! Not quite true if you've ever used the fantastic synthesised Racal 1772 compared to a valve Racal RA17, but generally he had a point.
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Old 22nd May 2022, 9:34 pm   #10
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Default Re: Reception on Shortwave

The switch mode power supply and broadband noise does seem to affect long wave and medium wave more than the shortwave bands.

The demodulated noise could affect the AGC and reduce the gain on LW and MW and give the impression that the radio has better gain on shortwave.
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Old 23rd May 2022, 10:14 am   #11
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Default Re: Reception on Shortwave

During the 1980's and 1990's working for BT we noticed that in some of the exchanges old domestic valved radios worked far better than their more modern transistorised counterparts. They seemed to cope with the weak Radio 1 or Radio 2 AM signals despite being surrounded by all the exhange equipment and its associated wiring. And they did not have to be located near a window to work.

As for all the SMPS and other electronic noise we have to put up with today I have noticed that its not just LW and MW that's badly affected but also the lower HF bands which are swamped out by high levels of noise all the way up to the 7MHz or 41m band. The noise levels tend to gradually drop off from 9MHz upwards.
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Old 23rd May 2022, 1:00 pm   #12
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Default Re: Reception on Shortwave

Quote:
Originally Posted by commie1 View Post
The point everyone usually misses(including me), is that solid state bjt's produce enormous amount of transconductance(gm), when compared to a valve or jfets and, infact, I would argue that bjt's produce too much gain where radio design is concerned.
You can also argue that valves and FETs produce astronomical amounts of current gain and are also troublesome.

Unwanted feedback tends to limit the gain of many devices. The tetrode then pentode were invented to screen capacitive feedback. So was the dual-gate MOSFET and the cascode amplifier topology.

But it's power which does the real work, not voltage alone, not current alone. So you have to look at power in to power out gain.

You can handle a device wih a rather large input impedance like a valve or FET by having a step-up transformation in a tuned circuit... not much problem in a radio which needs tuned circuits anyway.

You can handle a device with a rather low input impedance like a bipolar by having a step-down transformation in a tuned circuit. This means that the base voltage signal is low and that large Gm is reasonable.

Most valve RF amplifiers run a maodest amount of quiescent power, several mA at high voltage. Use a decent RF transistor at the same quiescent power and you'll get decent linearity. Go a step further and try one of the 'lossless feedback' types of RF amplifier (Look for patents by David Norton, and look in Pat Hawker's "Technical Topics" column of RADCOM) and now you can really have significant dynamic range that valves would have difficulty competing with.

So valves and FETs and Bipolars can all be used to give good performance. Circuit design techniques have evolved to suit each of them. Don't try comparing different devices in essentially the same circuit. This will make some look good and some lousy. Use the right techniques and they can all shine.

Ulrich Rohde (owns 50% of Rohde&Schwarz) has written a few books on receiver design and there are circuits in these which can show what can be done.

The first transistor HF radios were one mighty step backwards for mankind. When Racal brought out the RA217/RA1217 to replace the RA117. I own a 1217 and used to have a 117. Also the valved RA117 may have a stable LO and better filters, but its dynamic range was disappointing compared to HROs and AR88s. It's taken decades, but now higher performance receivers can be done with transistors than with valves. Transistor development and circuit development have continued long after valve development ended.

David
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Old 23rd May 2022, 7:05 pm   #13
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Default Re: Reception on Shortwave

Wow, what a comprehensive explanation David. I have learnt something. Thanks!
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Old 23rd May 2022, 9:12 pm   #14
commie1
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Default Re: Reception on Shortwave

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Originally Posted by Radio Wrangler View Post
You can also argue that valves and FETs produce astronomical amounts of current gain and are also troublesome.
At dc yes but with ac signals, the jfet input impedance becomes a cr circuit, a capacitor to ground.The higher the signal frequency, the lower the input impedance becomes.

Quote:
Originally Posted by Radio Wrangler View Post
Unwanted feedback tends to limit the gain of many devices. The tetrode then pentode were invented to screen capacitive feedback. So was the dual-gate MOSFET and the cascode amplifier topology.
If you look at the cascode topology, it is basically an attempt to reduce power gain of the stage. This is done because a single device will burst into oscillation otherwise.

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Originally Posted by Radio Wrangler View Post
But it's power which does the real work, not voltage alone, not current alone. So you have to look at power in to power out gain.
That is true, but usually if a device has a high gm figure, it is likely to have high power gain.

Quote:
Originally Posted by Radio Wrangler View Post
You can handle a device with a rather low input impedance like a bipolar by having a step-down transformation in a tuned circuit. This means that the base voltage signal is low and that large Gm is reasonable.
Matching input impedance will not compensate for a higher power gain device, actually it will serve to increase power gain, i.e., maximum power gain theorem, and so will become unstable and probably burst into oscillation.
Quote:
Originally Posted by Radio Wrangler View Post
Most valve RF amplifiers run a maodest amount of quiescent power, several mA at high voltage. Use a decent RF transistor at the same quiescent power and you'll get decent linearity. Go a step further and try one of the 'lossless feedback' types of RF amplifier (Look for patents by David Norton, and look in Pat Hawker's "Technical Topics" column of RADCOM) and now you can really have significant dynamic range that valves would have difficulty competing with.
With the AOR 7030 receiver design, John Thorpe put a 2n3866 pre-amp on it's front end with incredible local feedback in order to reduce it's power gain, if he hadn't then his entire front end would burst into oscillation.Again, power gain is reduced.
Quote:
Originally Posted by Radio Wrangler View Post
So valves and FETs and Bipolars can all be used to give good performance. Circuit design techniques have evolved to suit each of them. Don't try comparing different devices in essentially the same circuit. This will make some look good and some lousy. Use the right techniques and they can all shine.
If you still are not convinced, consider the Eddystone EC10, why square root the rf amp power gain using common base?, also, the original HRO front end uses 2 rf amp stages, try and get this circuit working using bjt's, I assure you, you will not succeed.Also, I should point out that early germanium bjt's had/have lower power gain than contemporary silicon epitaxial planar types.

Quote:
Originally Posted by Radio Wrangler View Post
The first transistor HF radios were one mighty step backwards for mankind.
That depends on the design team at hand, if I look over the 1965 HRO 500, I can see from their schematics that the design team were well aware of the high power gain of bjt's, I regard the HRO 500 to be a good solid state bjt communications receiver.

Last edited by commie1; 23rd May 2022 at 9:40 pm.
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Old 23rd May 2022, 11:08 pm   #15
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Default Re: Reception on Shortwave

All I can plead in my defence is 40+ years designing various high performance receiver systems. They can be found in the hands of the US military, national standards labs, NASA, JPL, AT&T (Bell) labs, etc. I assume that if there was anything much wrong with my approach, they'd have let the firm know.

I stand by what I've written.

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Old 24th May 2022, 7:12 am   #16
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Default Re: Reception on Shortwave

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Originally Posted by Bazz4CQJ View Post
Putting aside the technical problems of listening on SW now, what would you listen to? I think the modern term would be "content"; what can be found that's of interest?
I totally agree, I can get very good reception on SW on most of my 1930's sets but struggle to find anything I can be bothered to listen to!
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