Sensitivity of broadcast/domestic and communications receivers compared.

[Al (astral highway)]

This is a general question. What is the approximate difference in sensitivity between a decent vintage communications receiver and a decent broadcast receiver? Is it twice as good, five times as good, or greater?

Please can you give an illustration in uV or mV that can be resolved at the first RF stage. Also, what other features (electronically) does a comms receiver have that are not found in a domestic receiver with a shortwave capability? Obviously I'm taking selectivity for granted.

Period can be WWII onwards.

[Station X]

Googling "Communications Receiver" will probably reveal a lot about their features.

[Skywave]

Hi Astral -

That is a broad Q. which could take a lot of space to answer fully.
Graham's comment above should provide some answers.
Might I also respectfully suggest that you acquire a few classic text books on the subject of Receiver Design *. These will really help - and probably also provide answers to Qs. you haven't thought of yet!

* A quick glance at the bookshelf above me suggests:
Terman, Radio Engineering (& others); Scroggie, Foundations of Wireless; Langford-Smith, Radio Designer's Handbook; various by the RSGB or ARRL; Radio & TV Engineers' Reference Book, Hawker & Pannet; Electronic Communications Systems, Kennedy; Communication Engineering, Everitt & Anner - to name a few.

Al. / Skywave.

[Al (astral highway)]

Thanks Al. That is a helpful reading list, although with my other priorities, I'm frankly unlikely to have the chance to get through any of that any time soon.

I have owned my own LOWE in the past, so I'm practically familiar with what a comms rx can do, its selectivity and its noise rejection capabilities, and of course I know that it can resolve SSB, whereas a broadcast receiver can't.

I do have an overwhelming curiosity over the comparative sensitivity issue and can't now (having got rid of the LOWE) compare performance against performance.

Even a rough estimate of the relative sensitivity would be a great help.

[Paul_RK]

Well, taking one good and reputable but decidedly "domestic" receiver, the Hacker Super Sovereign, its spec. includes:

AM sensitivity -
MW/LW 3-7 microvolts for 10 dB S/N
SW1 (10.9-33m.) 5-8 microvolts for 10 dB S/N
SW2 (27.5-89m.) 4-7 microvolts for 10 dB S/N.

I don't know how readily other available figures will lend themselves to comparison.

Regards,
Paul

[Skywave]

Paul - To me, those figures look pretty impressive for a "domestic" receiver; they seem comparable to a mid-range comms. RX.

Astral - Yes, agreed - it depends on what one's priorites are; we all have our responsibilities & hobbies. One of my hobbies is collecting old radio books and studying theory. My real point to you is that by acquiring a couple of publications such as these, you don't have to read them from cover-to-cover in one sitting! Just keep them handy as a readily available sources of info. for when the need arises. None of us can remember everything on the Theory Front.

Al.

[XTC]

I haven't seen sensitivity figures quoted for domestic valve sets in their service notes, but here's a thread from a time back, where I did a rough and ready check on a Pye P76.

https://www.vintage-radio.net/forum/...read.php?t=321
It was 4mV to 15mV for 100mW output.

Comms receivers usually have a sensitivity spec in the manual. E.g the AR88 has a stated sensitivity of about 3µV for 20dB S/N CW and about 8 for AM. The exact values vary depending on the frequency, and they give tables.
To answer your question broadly, I'd say 20µV or less for a comms receiver and 20mV or less for a domestic AM receiver.

What features does a comms receiver have over a domestic receiver?
It depends on the comms receiver.
More than one IF stage, maybe with staggered tuning.
At least one RF stage.
Often a separate local oscillator valve for stability. Sometimes specially chosen components such as caps with particular temperature coefficients so the frequency remains stable
Sometimes a particularly rigid cast chassis because rigidity is important.
BFO, often with a neon stabilised supply.
Sometimes Noise limiter and crystal filter.
Switchable AGC sometimes with long and short delay.
Often an elaborate geared drive for the tuning cap.
Separate RF and AF gain.
Sometimes an S-meter.
Usually an aerial tuning control.
Very often a selectivity control.

Offhand I don't think I've ever come across a domestic receiver with a BFO or switchable AGC.

HTH, Pete.

[Al (astral highway)]

Hi Pete,

Thanks for taking the time to put this detailed answer together.

Originally Posted by XTC

To answer your question broadly, I'd say 20µV or less for a comms receiver and 20mV or less for a domestic AM receiver.

So a comms receiver is broadly 1000 times more sensitive. Crikey: that's way more than I had imagined.

And thanks for listing the features, also. Very interesting stuff. I'll also check the link you provide here.

All the best

[Mark_4CX35000]

Many of the details on the Lowe range of receivers can be found here
http://www.arar93.dsl.pipex.com/mds9...ent/lowe1.html

[Skywave]

Originally Posted by astral highway

So a comms receiver is broadly 1000 times more sensitive. Crikey: that's way more than I had imagined.

Yes - "more sensitive" purely in terms of voltage gain: 60dB in this case (don't be over-impressed with the number "1000"; remember that our hearing is logarithmic; "60" 'sounds' a lot less than "1000"). Compared to a domestic / broadcast receiver, a comms. set will have (typically) an RF stage (or more than one) and at least 2 IF stages. Let's do the sums: allow 20 dB for the RF stage; 40 dB for the IF amp - and hey presto! that's an extra 60 dB.
And even that assumes the same IF bandwidth.

Al.

[Peter.N.]

Sensitivity is not the only consideration of course, things like tuning bandwidth and spurious signal rejection are also important.

[Al (astral highway)]

Originally Posted by Skywave

Yes - "more sensitive" purely in terms of voltage gain: 60dB in this case

I see your point, Al, but I was looking at the smallness of the signal voltage and in absolute terms, 20uV and less seems very small indeed (although I do recall that I needed an extra stage in front of a comms receiver to detect carrier waves from moribund satellites and I wonder what signal size we were dealing with there? )

[GMB]

If you are impressed by 20 µV then you might like the early valve Yaesu ham radio transceivers quoting rx sensitivity of 0.5µV for s/n 10-20dB.

[XTC]

One of the main problems with comms receiver design is front-end noise. it's easy to increase the sensitivity by adding stages, but that's no use if it also increases the noise. There's a big difference between a set which claims 10µV @ 6dB S/N and another which does 10µV @ 20dB

Comms receivers and domestic receivers are designed for different jobs and to different budgets. One's designed to recover intelligence from very weak signals and cost, styling, audio quality and ease of use are secondary. Very often they were bought by governments or large companies. Domestic receivers are appliances and pieces of furniture. Ease of use, eye appeal, reasonable cost (because people are spending their own money) and decent reproduction from powerful stations at most a few hundred miles away are important.

Are you sure that the device for picking up satellites is an amplifier and not a frequency converter?

Pete.

[Al (astral highway)]

Originally Posted by XTC

Are you sure that the device for picking up satellites is an amplifier and not a frequency converter?

You're right, it is a converter (diagram attached) but doesn't the nuvistor stage add rather a lot of voltage gain? Ignoring the local oscillator and mixer, I thought this might equivalate to an additional RF stage in the comms receiver that this is intended to feed to.

https://www.vintage-radio.net/forum/...4&d=1201795663

Your analysis of the design differences between the two types of sets is very interesting and lucid. Thank you.

If the functional spec is so clearly defined - the difference between detecting strong, nearby signals vs weak, distant signals - then the obvious differences in cost, component count & sophistication make a lot of sense.

[Al (astral highway)]

Originally Posted by GMB

... you might like the early valve Yaesu ham radio transceivers quoting rx sensitivity of 0.5µV for s/n 10-20dB.

Impressive indeed. I will start looking for one!

[Sean Williams]

http://www.arrl.org/tis/info/pdf/0003069.pdf

This is a report relating to the Elecraft K2 Transciever - A kit radio built by at least two of us here - Performance equal or better than a commercial product costing two or three times more!

Still regarded as the best reciever in the amateur market!

[Al (astral highway)]

Originally Posted by Sean Williams

This is a report relating to the Elecraft K2 Transciever - A kit radio built by at least two of us here ...

Still regarded as the best reciever in the amateur market!

Incredible. Thanks Sean. I'm guessing these aren't still available as kits..? (mind you, it would seem a bit of a waste as I don't have a ticket to TX)

[Sean Williams]

Yep, still available, and good fun to build too!

[XTC]

Originally Posted by astral highway

You're right, it is a converter (diagram attached) but doesn't the nuvistor stage add rather a lot of voltage gain? Ignoring the local oscillator and mixer, I thought this might equivalate to an additional RF stage in the comms receiver that this is intended to feed to.

https://www.vintage-radio.net/forum/...4&d=1201795663

Just looking at it, the nuvistor stage must introduce some gain, but I'd guess it's partly offset by losses elsewhere in the circuit. So yes, it's a pre-amp and converter by the looks of it.

If you are interested in picking up satellite transmissions, then a receiver, however sensitive and quiet, is only part of the story and a decent aerial system to feed it would be important.

I suppose that's another difference between comms receivers and domestic receivers. Domestic receivers frequently have an internal ferrite rod or frame aerial, because it's compact and tidy. Comms receivers are expected to be used with an outside aerial.

Pete.