Frame aerial Crystal set.

[pwdrive]

Out of interest there's a thread running on another forum about matching the output of an xtal detector with an audio transformer...Main thread:

http://theradioboard.com/rb/viewtopic.php?f=2&p=65571&sid=2575c6f029dcee289441b024fb0e6734#p65571

Link within that thread worth a look:

http://theradioboard.com/rb/viewtopic.php?f=2&t=4277&p=38595&hilit=mak1939#p38595

I'll post this on UKVRR forum as well.

Lawrence.

[Pat Pending]

I posted a link to your topic in a few places Trevor, but the one I have most hope for is the radio board, (Lawrence has got the jump on mentioning them I see!), there is a membership of knowledgeable personalities who frequent the crystal set forum there, and I would expect there may be some who will give your ideas a try, and possibly respond or start their own topic prompted by your ideas. The only loop antenna that I have recently tried that works as well is one from the TRB moderator, Jim Kearman that uses an RF transformer to increase the inductance of a given loop, details at http://kr1s.kearman.com/html/hooploop.html . 

Lawrence is on the money as far as his comments re the rf transformers function of transferring the signal as efficiently as possible so as to preserve the selectivity of the tuned circuit, but I still can't get my head round why its better at it than doing the same thing with the link winding. 

I tried the loop with an Mullard OA10 switching diode, it seems quite a bit better in listening tests, for volume, than the 91 I'd been using, possibly has a slightly lower vf, maybe maybe worth your giving one a try Trevor. 

Regards. Andy.

[radioman]

I was visiting Trevor earlier today and got a demonstration of this ....
WOW is what I can say, this is without doubt the best performing crystal set I have ever heard !
Admittedly, the high impedance vintage 'phones being used were the best from the selection that were to hand but you could easily make out the stations being received and the program material - it was far louder than my own genuine crystal set with long wire antenna.
Just for fun, I suggested trying a loudspeaker instead of the 'phones...
OK, it was a BIG 12" KcKenzie GP 'speaker, as these are usually more sensitive than smaller ones (in this case ~100 db/w). This one has a very large magnet with an aluminium centre cap.
I wired up an output transformer in 'auto' configuration.
It wasn't very loud but did actually work !
Trevor kindly gave me a ferrite toroid the same as the one he used so some experimentation of my own is on the cards... watch this space !

Andy

[Murphyv310]

Hi
We had a good day, albeit curtailed by picking up Anne and a visit to the DWP! I think Andy was impressed by the frame aerial crystal set.
Later on I had a rake around in the loft and found another pre-war set of headphones, well these are the Dogs ******** and have given me a little more audio. They are of German manufacture with a 4k impedance marking.
Impressive as I can hear clearly two French stations tonight!
This has spurred me on to try a two metre circular tunable frame aerial for both Medium and Long waves.
Watch this space too

[Murphyv310]

Hi.
Because of the great weather today I had a few ideas to try out. I rewound both primary & secondary. The main winding had 0.75mm single cored wire and the secondary some very thin multi stranded wire. This time I replaced the primary with 0.5mm single cored cable and the secondary with the 0.75mm single cored wire. All connections have been shortened to the tuning cap and the I've improved the tension on the wires.
All this has given me around 20mv increase to the detector on the strongest signal and improvements to all audible stations.
I'm hoping to fiddle about with the toroid perhaps this week although I have two hospital appointments in Clydebank, Tuesday & Thursday for a pre op and scan.

I did have a go at three turns and some short wave stations were audible.

[Pat Pending]

Good show Trevor! I've been given a few pointers from a member of the "crystal" fraternity, and have made myself some "litz" cable out of the fine wire on an old contactor bobbin, I'm going to build a new frame so that when I wind the new wire I can do a side by side test. I hope the hospital visits go well for you.

Regards. Andy.

[Murphyv310]

Hi.
It's been a few months since I posted on the topic.
Since then and after some recuperation from my heart bypass I have been trying different things.
All sorts of different detectors have been tried from germanium diodes, silicon, germanium transistors to those supposed wonderful ADL110900 Mosfet devices.
The best being a selection of germanium diodes. The frame itself seems best with a decent primary, thinner wire reduces output and how you couple the secondary also makes a difference.
There is also a way of improving output very slightly on the weak stations, that is by wiring the secondary of the loop to the secondary of the toroid in series, for some reason it works, I've experimented with different turns ratios on the toroid but output can be a trade off for selectivity and vice versa.
I think now it is at its optimum and I actually use it as a tuner for my Mullard 3-3 amp, the audio quality is outstanding, biggest problem is its size, hardly portable.

Now to baffle the boffins!! This will actually transmit, if you tune into a station and then tune a radio into the same frequency and have it close to the frame aerial it will modulate the carrier if you speak into the phones. It does work and was demonstrated to Andy last week.
Since then I have used the frame main winding connected to a simple RF oscillator and tried it this way, it works extremely well with superb audio quality albeit with only a few feet range.
I was actually thinking of making a smaller one for a pantry transmitter.
All good fun.

[Murphyv310]

Hi.
Thread revival!!!!
I've been playing about with the frame aerial again.
What I've discovered is the single turn winding is not required when using a toroid to do the matching. The single turn is not that efficient so using one turn tapped off the innermost part of the main winding is all you need. This is then fed to a winding to the toroid. A secondary can then be wound on the toroid just like on the original.
Overall the sensitivity and volume are higher and depending how you work out the turns ratio and load, selectivity can either be improved or traded off for greater volume.
I've a few different Ferrite rings to test to see if any further improvements can be made.
I'd like to try a piezo headphone but all I have is those rubbish crystal earpieces, results with the German phones are very good.

[Ed_Dinning]

Hi Trevor, I know it's cheating, but look up the TL431 chip used in linear mode with a crystal set. Run off 3 volts it will easily drive lo Z phones.

ed

[Murphyv310]

Really Ed..... I'm intrigued.