Sensitivity of broadcast/domestic and communications receivers compared. - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Al (astral highway) · 21st Nov 2008, 3:32 pm

Pete, that's a good point about the different design expectations over aerials for domestic and comms receivers.

I don't want to go off-topic here, but one of my conclusions when I built the satellite-listening converter last year was that I'd had good results but to go after the feeblest carrier signals from satellites with moribund power plants, that were initially launched in the sixties, I would indeed eventually need (a) a top-spec comms receiver to go behind this coverter and b) to build an aerial fit for the purpose. That's when it became a much-longer term project than I'd initially thought.

Before I started this thread, I was at the point of weighing up whether it was worth building a six to eight valve set (not including audio amplification) designed specifically to listen in to 140-220Mhz -- especially ultra-feeble, long-distance signals. AM only.

Instead of re-inventing the wheel, I was thinking of adapting a radar receiver design from the early war, before microwaves frequencies were adopted.

XTC · 21st Nov 2008, 4:58 pm

It depends on what your motivation and interests are. For instance, if I were interested in picking up these satellite transmissions, I'd be inclined to look into the aerial to begin with and use it, at least at first, with my Yupiteru scanner. The scanner is very sensitive and very stable. However, what we want to get out of these projects is a personal matter.

I've seen discussions about building comms receivers on this forum and I've thought about it sometimes. My view is that you could spend a lot of time and effort and probably be frustrated by debugging problems and mechanical problems in the end.

I think it's like asking whether you can build a lab-grade RF generator to the standard expected in the 60s and 70s - the circuits are fairly simple. The circuits may be simple, but the mechanical implementation needed for it to be stable, have accurate attenuation and produce no spurious radiation, is all far from easy. Added to which you can buy a lab-grade RF gen of that age for not too much.

If you want a ready made valve comms receiver to pick up these frequencies there's the Eddystone 770R (VHF) and 770U (UHF) which I've seen around for about £100 and I've also seen an RCA using acorn valves for about the same price. The Eddystones have a reputation for being a bit deaf. Then there are military sets which work on VHF. The R1132 comes to mind, but I'm not sure what its coverage is.

Other than that, I'm sure there are ARRL, Radcom, or other published designs which cover the range you need, but if you feel like making one from scratch, or using an early radar design, that's what you want to do.

Pete.

Al (astral highway) · 21st Nov 2008, 5:49 pm

Quote:

Originally Posted by XTC

My view is that you could spend a lot of time and effort and probably be frustrated by debugging problems and mechanical problems in the end.

I think you're absolutely right.

Quote:

Originally Posted by XTC

... The circuits may be simple, but the mechanical implementation needed for it to be stable, have accurate attenuation and produce no spurious radiation, is all far from easy.

I know exactly what you mean.

I have long been amazed by the build quality of even simple devices like Marconi's early valve voltmeters, and blown away by the compactness, robustness and ingenuity in the build of early UHF receivers like the R1132 (I have seen one of these close up)

I think this last post of yours has helped me to clarify that I'm trying to do two things at once : 1) extend my own ability in applied construction in suitable increments. (Hence the appeal of a complicated UHF receiver, even if it's not relatively capable by today's standards.

2) capture remote and feeble signals by any means.

In light of what I've learnt from this thread, and especially from GMB's and your comments (for which thanks) I think 2 isn't going to be met by building my own vintage design.

An expensive but possible option is to get a kit (Sean's recommendation - thank you - although very expensive, is one possibility) or follow up on some of your leads.

This being the case, I have all sorts of options to choose from to fulfil 1. I do want something that has some potential for bugs and surprises and does call for an exactingly high standard of build in order to work. The circuit doesn't have to be elaborate, hugely modular or showy to satisfy these conditions.

Thanks everyone who has contributed to this so far!

21st Nov 2008, 3:32 pm	#21
Al (astral highway) Dekatron Join Date: Nov 2006 Location: London, UK. Posts: 3,496	Re: Sensitivity of broadcast/domestic and communications receivers compared. Pete, that's a good point about the different design expectations over aerials for domestic and comms receivers. I don't want to go off-topic here, but one of my conclusions when I built the satellite-listening converter last year was that I'd had good results but to go after the feeblest carrier signals from satellites with moribund power plants, that were initially launched in the sixties, I would indeed eventually need (a) a top-spec comms receiver to go behind this coverter and b) to build an aerial fit for the purpose. That's when it became a much-longer term project than I'd initially thought. Before I started this thread, I was at the point of weighing up whether it was worth building a six to eight valve set (not including audio amplification) designed specifically to listen in to 140-220Mhz -- especially ultra-feeble, long-distance signals. AM only. Instead of re-inventing the wheel, I was thinking of adapting a radar receiver design from the early war, before microwaves frequencies were adopted. __________________ Al

21st Nov 2008, 4:58 pm	#22
XTC Retired Dormant Member Join Date: Oct 2004 Location: Bristol, UK. Posts: 837	Re: Sensitivity of broadcast/domestic and communications receivers compared. It depends on what your motivation and interests are. For instance, if I were interested in picking up these satellite transmissions, I'd be inclined to look into the aerial to begin with and use it, at least at first, with my Yupiteru scanner. The scanner is very sensitive and very stable. However, what we want to get out of these projects is a personal matter. I've seen discussions about building comms receivers on this forum and I've thought about it sometimes. My view is that you could spend a lot of time and effort and probably be frustrated by debugging problems and mechanical problems in the end. I think it's like asking whether you can build a lab-grade RF generator to the standard expected in the 60s and 70s - the circuits are fairly simple. The circuits may be simple, but the mechanical implementation needed for it to be stable, have accurate attenuation and produce no spurious radiation, is all far from easy. Added to which you can buy a lab-grade RF gen of that age for not too much. If you want a ready made valve comms receiver to pick up these frequencies there's the Eddystone 770R (VHF) and 770U (UHF) which I've seen around for about £100 and I've also seen an RCA using acorn valves for about the same price. The Eddystones have a reputation for being a bit deaf. Then there are military sets which work on VHF. The R1132 comes to mind, but I'm not sure what its coverage is. Other than that, I'm sure there are ARRL, Radcom, or other published designs which cover the range you need, but if you feel like making one from scratch, or using an early radar design, that's what you want to do. Pete.