Is there any analog radio receiver that prevents fading of the SW reception?

[ofosot69]

Prabhat Karpe <prabhatkarpe4@gmail.com>​ ​	4:34 PM (12 minutes ago)
to me

I have been using AM radio receivers for a long time but I have encountered fading many times while listening to the SW reception. However, I have noticed that the most expensive radio receivers from Tecsun, Degen, and Sony minimize fading up to certain extent. So, why does it happen? Is it something to do with the AGC or the sensitivity?

I would also like to know whether an AM radio that uses vacuum tubes instead of transistors, can have a better reception quality?

 

[Nigel Goodwin]

Prabhat Karpe <prabhatkarpe4@gmail.com>​ ​	4:34 PM (12 minutes ago)
to me

I have been using AM radio receivers for a long time but I have encountered fading many times while listening to the SW reception. However, I have noticed that the most expensive radio receivers from Tecsun, Degen, and Sony minimize fading up to certain extent. So, why does it happen? Is it something to do with the AGC or the sensitivity?

Both, if it's more sensitive the AGC will turn the gain down, giving it more range to turn it back up as the signal fades. Better radios are more likely to be more selective as well, particularly proper communications receivers which are likely to be much better performers all round (there are reasons why they cost so much).

I would also like to know whether an AM radio that uses vacuum tubes instead of transistors, can have a better reception quality?

It 'can', but it's unlikely to - though certainly an expensive well designed valve receiver will out perform a cheap transistor one - but a well made and well designed modern transistor receiver should outperform any valve receiver (other than in the case of a Nuclear EMP ).

 

[danadak]

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Not "analog" example per se....

Regards, Dana.

 

[aliarifat794]

A vacuum tube radio may offer a unique sound signature but does not necessarily provide better reception or minimize fading

 

[Miles Prower]

I would also like to know whether an AM radio that uses vacuum tubes instead of transistors, can have a better reception quality?

Depends on what you mean by "reception quality", and what the solid state design is. A vacuum tube oscillator will produce less noise than a phase locked loop (PLL) design. The PLL has the advantage of being able to produce a wide choice of frequencies, useful for fixed channel services such as CB or aviation communications. The drawback is that the PLL is a servo mechanism, and like all servos, it goes out of control once the error signal disappears. The PLL will therefore generate small frequency variations around a center frequency. This incidental FM generates sidebands (phase noise) that can mix noise into the receiver.

(PLL phase noise is your problem in a receiver. If the PLL is the master oscillator of a transmitter, it becomes everyone's problem. A max legal ham rig can elevate the noise floor across an entire band for miles around. The phase noise may amount to 1.0uW, and that doesn't seem like much, yet a run-of-the-mill comm reciever can detect signals down to 10^-15W.)

A vacuum tube oscillator operates in a self regulating, gain saturated mode that pretty much eliminates incidental AM that plagues BJT oscillators that have to operate in Class A. If your VT oscillator has a substantial, preferably with brass plates, tuning capacitor that readily radiates heat, and an air coil, you can drive it hard enough to eliminate phase noise as well. You'll have a quieter receiver. Of course, there are work arounds for solid state that overcome these limitations.

AM reception also depends on the linearity of the IF stage(s). THD introduced at IF frequencies becomes audio THD after demodulation. Here, VTs beat transistors in linearity, and produce less THD.

If you're referring to audio quality, again, that depends. For comm receivers audio quality isn't a consideration since modes such as SSB produce horrid audio quality, but that's OK so long as the received signal is intelligible. High fidelity AM on the ham bands isn't needed nor is it legal. Thus, most comm receivers, whether hollow state or solid state, have rudimentary audio subsystems that won't give superior sonic performance. Receivers that are designed with sonic performance as a design criterion are usually "tuners" that are intended to be connected to an external amp.

 

[rjenkinsgb]

A vacuum tube oscillator will produce less noise than a phase locked loop (PLL) design.

Surely that's down to the RX or TX using an analog tuning / VFO vs. PLL, rather than valve (tube) vs. solid state device??

 

[Miles Prower]

^^
There are work arounds for SS VFOs, such as including tuned RF amps/buffers, and filtering that can reduce the extra noise you get from SS. Even if you decide you need a PLL to get the job done, you can use or design a good one rather than some off the shelf design that generates excessive phase noise. You could also opt for direct digital synthesis.

Back in "The Day", phase noise was a problem when using crystal oscillators (such as the "Novice" class ham licensees were restricted to using). Driving the crystal too hard would break it or cause excessive frequency drift (what you want avoid by using crystal control in the first place) soft enough to prevent that meant phase noise.

What you don't see (except for the cheapest designs) is a solid state oscillator connected directly to whatever it's supplying s signal. That was very common in VT designs.