Simple AM radio

Southgate News carries a report of someone's first steps into RF by building a simple TRF circuit. It uses a TA7642 TRF IC, which is like a ZN414 that some may remember. These form the basis of very simple TRF receivers. I recall making a similar circuit years ago for Medium Wave. As I recall, mine was fix tuned to Radio Cambridgeshire. I guess these ICs could be used for a simple RX in a 160m AM rig.

See http://southgatearc.org/news/2019/april/making-a-simple-am-radio.htm#.XLuJ7fZFy00

MW broadcasters going?

Several broadcasters are leaving MW, instead concentrating on FM, DAB or the internet. The latest reported via Southgate News is a Belgian broadcaster on 621kHz.

This will eventually free up spectrum, perhaps for amateurs (?), but it also means the end of reception on extremely simple receivers like crystal sets.

I well remember falling asleep listening on my crystal set.

Miracle Whips and derivatives/copies

A 56 inch long whip can only behave like a 56 inch whip. This is a basic law of physics. What the Miracle Whip (MW) and its derivatives do is match this whip on the HF and VHF bands. With a decent ground or counterpoise wire the MW may be only a couple of S-points down on a "decent" antenna on the higher HF bands. They work reasonably well and, in the past, I used my MW quite a bit, even from indoors.  They are definitely NOT a miracle antenna, although they are not too bad.  Since the owner, a Canadian called Robert, died there have been a few newcomers in the market.

Would I buy one today? Probably not. I have had better results with small loops.  As a simply deployed mainly RX antenna they make an ideal companion for an FT817 or similar. Their beauty is their simplicity. If you want optimum performance in a small antenna there are better solutions.  Small loops seem to work better, but then bandwidth becomes very narrow although loops don't need grounds or counterpoises to work well. Personally, at QRP levels I'd use a loop every time.

As Wheeler showed years ago, efficient small antennas are reactive and unless losses are minimised, efficiency suffers. This is a fundamental limitation. Although high permeability ferrites and high permittivity ceramics can help to alter the size of space near an antenna and "magnify" the effective size of small antennas, the effect is small unless there is a lot of ferrite with high permeability or a lot of ceramic with a high permittivity. In theory, a tiny antenna can be very efficient but you'd need superconductors and lossless capacitors!  At the moment, sadly, neither are practical for mortals!

See https://sites.google.com/site/g3xbmqrp3/antennas/mwhip .

AM broadcasts on Medium Wave

The BBC recently switched off some of its MW local radio AM outlets for some weeks to see if anyone was listening. Results suggest few people listen to their radios in the UK on Medium Wave any more. I know I am one of them, preferring to use Band 2 FM. We also have a DAB radio but it is pretty useless in the kitchen where FM is perfect. I think it is a signal strength issue.

So, will the BBC switch off all its MW output? Will anyone care? It may soon be that AM will be a dying mode unless we radio amateurs use it and show its strengths.

See www.theregister.co.uk/2012/11/08/dab_am_bbc/.