Hi Guys
True or False? and why?

I am trying to learn about transformers including pulse transformers,
and inductive pickups on the likes of GDO equipment.
That one is true!

1) Any loop antenna which presents as DC short circuit is
magnetically coupled with the transmission antenna.

2) The secondary winding sharing the same ferrous core
as the primary winding transfers current from the primary,
and that is the only way a megnetic coupling effectively
transfers current from the primary to the secondary.

Cheers, Brek.

As you seem to have realised Magnetic and capacitive induction does not actually need a physical core like ferrite, or iron and frequency is a factor.

All you need to get any form of induction, from one wire to another, is a dynamic magnetic field. There are plenty of IF transformers called air transformers as both coils are mounted on wood, ceramic, or unfortunately, in later radios, plastic formers which are in many cases deteriorating & crumbling.

The flicking CFL tube is a classic example of capacitive induction. We will insist upon bundling AC mains wires together & parallel, so the dynamic magnetic field that exists in one wire will induce power into the other.

As there is no current flow of significance the power moves to a higher order manifesting as pressure. This pressure viz. EMF builds up until it reaches the ionisation potential of the gas in the tube and it flashes. So we have created a relaxation oscillator, as that keeps repeating at a frequency controlled by the amount of induction available.

Filament globes never did that as they are a constant resistive load on the circuit. Naturally you are paying for this leakage. So theoretically it will add inefficiency if you run an AC wire parallel to a metal pipe (Capacitor formed).

What is GDO equipment?

Ian

Thanks for the reply Marcc, I have to venture into territory of
either design or tuning, or filtering a pulse transformer with the
objective of noise immunity. The desired pulse alwsys has the
same rise and fall time.

Since the inductive pickip is an inductive loop,
and then transformer (toroid) coupled to a sense circuit,
it's beginning to look like a radio front end from the
loop antenna to the first transformer coupling or ferrite loop,
and tuning for a padticular frequency is certainly achieved in radio!

Ian, a GDO (Grid Dip Oscillator) is a set of interchangeable coils and amplifier
used to radiate some energy to another tuned circuit under test often to determine
resonant frequency.

If this is similar to a switch mode I have not seen a lot of them that do not create RFI, I had a shot at one mob yesterday as a current LED work light I bought, is pumping out hash on the FM band. Have not yet investigated AM.

Wall Wart, FAX, Digital set top box & the Kitchen fridge are all RFI radiators here. I do get the impression that the ones supposed to be regulating this are asleep at the wheel.

Putting the thing in a Faraday cage may help, but the fax was using the phone line as an antenna so you may need to use an inductive filter eg ferrite to tame it? I get a lot of RF riding on the mains here & its a combination of capacitive & inductive filters to get it out.

Marc

Re GDO, I should have said oscillator, not amplifier.
It only needs a valve or silicon to ring it's tank circuit.

The stuff I'm making is caged, or else it can receive and transmit
unwanted noise between the same project.

I've read some ammateur tests about partial caging
where it was claimed a three sided cage blocks approx
85% of noise transmitted from outside, as a complete cage.
(experiment at 100kHz).
He also claimed the bottom of the cage is more important than the top.
Interesting stuff.

MW broadcast interference has never been an issue here,
and if I may rub in some salt, I get great reception with any wire
completely concealed in a floor standing console.
MW antennas I've made were just for experiment,
I especially like tuned loops.

Reception on AM only has problems with WA here as there is a Granite hill that seems to soak it up. It is also good at blocking TV & FM on the other side of it.

The major issue is a lot of transmitters & 24KV aerials that seem to drag them in as RF & that all ends up sneaking into the mains after the transformer. I probably am not helping by having about 600m of 240V aerials on my side of the utility transformer.

I tend to use long wire antenna's for AM as I have the room, but there is such a thing (according to the RCA chart) as too long, so one needs to watch the frequencies or it will attenuate rather than receive. There is also the risk of it being the lightning umbrella. So I will ground it during a lightning event & I have seen them & the 24KV ones trailing St Elmo's fire.

In the last Signal tracer, generator, detector, I made I made a point of shielding the RF, Decoupling the power & adding RF chokes to ensure that any RF that did get try to get into the audio would be attenuated and not amplified. That is more an issue with valves as many used in audio are not too particular & will amplify RF at quite high frequencies, which quickly manifests if decoupling & shielding a poor.

Marc

Did we arrive at an answer for Q1?

If that is true, and I think that it is, it means that the antennas of a transmitter and receiver
on opposite sides of the world for a single transformer, and furthermore, that transformer has
a number of secondaries depending how many people with magnetic loop antennas are tuned in.

I have been experimenting, and can read feedback of with the same micro controller that is generating the pulse...
to make a core rope ROM with a single controller.

https://www.youtube.com/watch?v=5npB3TpxfKw

Hi Art,

I'm up for a theorical discussion any day, anmd this one seems to be in the too hard basket. However, I'm unsure if I understand the question ...... which I am probably about to demonstrate via a couple of maybe dumb questions .....

Firstly, I believe I understand how a Grid Dip Oscillator functions. I have several and have used them to varying degrees of success. I am talking about a small hand-held device for testing resonant circuits etc. If other types exist, then I have no idea about them.

"...... Any loop antenna which presents as DC short circuit ..." do you mean an antenna which presents a very low resistance, a continuous piece of wire, no breaks??????

"..... coupled with the transmission antenna" are you inferring that a GDO has a transmission antenna AND a receiving antenna (loop)?????

My understanding of how a GDO functions is that when, say, an external resonant circuit is close enough to the GDO coil(inductor) but not near the resonant frequency, then energy is transferred to the external circuit via magnetic coupling ..... current generated in external circuit etc.. BUT when the GDO frequency approaches the resonant frequency of the external circuit, say, a parallel LC, then the impedance within the parallel circuit increases and the transfer of energy drops, hence a 'dip' is seen on the GDO.

Then again, I maybe on the wrong track ..... Either way, I would like to know also.

Cheers,
Ian

Yes the resonant LC steals energy from the GDO tuned to the same, or close f.
You explained the same way I understand it.
In the same context as the question 1, I’m also calling the GDO coil, and the LC coil, a single transformer.
It’s a semantic question,

Now if you put that GDO and the LC under test in the same enclosure, then everyone would call that a transformer without a doubt.

A magnetic loop antenna is a DC short circuit yes, low resistance for DC.
The ferrite bar loopstick in AM radios is a very common example of this.