Got to ask

[ericmark]

Years ago in the days of AM radios I built a radio using a bog role a few turns of wire on it a germanium diode and crystal ear piece. Fine tuning done with a bit of steel inside the bog role.

Try google crystal set radio and you will find the design.

Clearly the reverse can also be done one can transmit as well as receive.

The move to digital has reduced transmit power required by broadcaster and also increased power needed to receive. With such low powered transmitters it is not surprising that other items can knock them out.

I personally can't see the point in DAB radio. There is a good transmission on UHF with freeview, another on satellite plus the orignal FM signal on VHF so why add another duplicated signal half way between FM radio and Freeview TV it's just a waist of spectrum.

 

[SimonH2]

... the transformer (I'm assuming a compact electronic jobby) which will be designed to supply incandescent lights (ie a resistive load) and the LEDs which will be very much not a resistive load*.
* Even if they are marked with CE markings etc, they coudl well be "cheap and nasty" lights that have been built without any PFC or filtering.

I'm not totally sure what you meant by that. LED lights will certainly present a non-linear load (which could be relevant), but there is unlikely to be a significant reactive component to the load.

What I mean is that the load will really not look much like a resistor at all - on a macro scale it probably has a negative impedance as current will reduce if voltage increases and vice-versa. The incandescent lights look fairly much like a resistor, and just having the 50W one on the circuit will almost certainly provide enough stabilising effect to keep everything happy.

As bernardgreem points out lower down the page, there is now a switch mode supply feeding other switch mode supplies. There will be interaction both between the "transformer" and the lights, and between each light and the others.
Easiest way to deal with that is to use a wirewound transformer for the supply which will do away with most of the noise.

I personally can't see the point in DAB radio. There is a good transmission on UHF with freeview, another on satellite plus the orignal FM signal on VHF so why add another duplicated signal half way between FM radio and Freeview TV it's just a waist of spectrum.

So was freeview (DVB-T) when it started. Long term the plan is to do to AM and FM radio what's been done to analogue TV - so they can flog off some more spectrum to the highest bidder. Even without doing away with FM, there wasn't enough spectrum to allow the number of stations that are (or were expected) on digital.
Since satellite and DVB-T on UHF aren't very useful for mobile use, there's a place for DAB+. Note I said DAB+ - I can't see the point in sticking with DAB when there's something much better (and other countries are using it making DAB-only sets somewhat limiting for the international traveller). There should at least be some sort of regulation requiring new receivers to be DAB+ capable rather than just DAB.

 

[JohnW2]

I'm not totally sure what you meant by that. LED lights will certainly present a non-linear load (which could be relevant), but there is unlikely to be a significant reactive component to the load.

What I mean is that the load will really not look much like a resistor at all - on a macro scale it probably has a negative impedance as current will reduce if voltage increases and vice-versa. The incandescent lights look fairly much like a resistor, and just having the 50W one on the circuit will almost certainly provide enough stabilising effect to keep everything happy.

Exactly - as I said, a non-linear resistive load (i.e.'not like a resistor'), not one with significant reactive components (which is what is normally understood by 'non-resistive').

Kind Regards, John

 

[SimonH2]

True, in electrical circles you might take "non-resistive" as meaning reactive - as in poor power factor. In this case I mean it probably looks nothing like a resistor - not something that's non-linear (which would imply resistive but varying in value), but something that's quite complex.

If they are like a lot of 'cheap' SMPS then it'll have a very high crest factor/very poor current waveform, and a lot of harmonics. And that's just from the rectifier/capacitor front end. It's probably going to spit out a lot of switching noise as well, a good chunk of which will be shoved up its supply to upset the SMPS that's feeding it.

 

[JohnW2]

True, in electrical circles you might take "non-resistive" as meaning reactive - as in poor power factor.

Well, in electrician-talk it may mean 'poor power factor' - but in terms of physics, electrical engineering and electronics there's obviously not necessarily anything 'poor' (or bad) about having an impedance which has significant (or even predominant) reactive components - it's just a fact

In this case I mean it probably looks nothing like a resistor - not something that's non-linear (which would imply resistive but varying in value), but something that's quite complex.

Agreed.

If they are like a lot of 'cheap' SMPS then it'll have a very high crest factor/very poor current waveform, and a lot of harmonics. And that's just from the rectifier/capacitor front end. It's probably going to spit out a lot of switching noise as well, a good chunk of which will be shoved up its supply to upset the SMPS that's feeding it.

All true. Indeed, even high quality switched-mode PSUs are not necessarily all that 'quiet'! As I said way back, if the OP's digital radios don't have any external aerials, they are probably dealing with such relatively low signal levels that it wouldn't take much to 'tip them over the balance'! Indeed, they may even effectively be using the mains wiring as their antannae - which could obviously be bad news iof they happen to be 'RF noise - ridden'!

Kind Regards, John