Ferrite sleeve loop antenna

[murphyv310]

Hi Andy.
I did try a single turn in the centre of the windings but it didn't work well.
Could it be the litz wire? I noticed on your trace the actual signal from noise floor to peak is virtually the same as the result from the single rod only the noise floor is higher so are we looking at a signal above the noise floor but not actually a higher true signal?

[Andrew2]

If anything I think the Litz wire should help. Re the traces, they were made in the shack where the noise is high, and both aerials were subjected to the same external noise level. A more gainy aerial is bound to bring up the noise so you're not going to hear any advantage. Once you get out to a low noise place you see the difference. You are able to put more signal into the receiver while still keeping the noise relatively low.
I experienced this when I used my portable radio to listen to a distant AM net on Topband. Without the sleeve aerial the signals were barely above the receiver noise (this was at the far end of the garden with the nearest neighbour about 50 yards away so the external noise was very low), but with the sleeve aerial placed near the radio the stations were fully readable.

[murphyv310]

Hi
I'm beginning to agree with the initials of this project.
FSL.... Financial Sinkhole Loop! The cost of the 660/46 Litz is eye watering, ferrite rods are expensive as well.
I did make up a 16 rod one today using plastic plumbing pipe fully expecting it would be poor but in fact its performance wasn't far short of the one I made on the glass jar with 25 rods.

I've put up a wanted for some 660/46 Litz, would be happy enough to eventually buy more if someone has a spare 15 feet for a reasonable price, so I can try this out with the recommended wire. If it doesn't work out there will be some bargain ferrite rods going.
Another question is it worth a try super glueing a number of two 100mm rods to get 200mm and making up another this way, would this Increase output?

[murphyv310]

A possible source for litz wire is from induction cookers. Not sure of the spec used but perhaps a visit to a recycling centre would be in order.

[kalee20]

Originally Posted by Andrew2

Re the 2mm spacing between the rods - I tried with and without and could detect no difference.

I'm wondering about that, too - what would a gap do?

Usual reasons for a gap in a magnetic core are (1) to stop eddy currents from causing losses, and (2) to reduce effective permeability so that the inductance is predictable (and core saturation is avoided). But neither of these apply here, ferrite is already high resistance so eddy currents are negligible, and a coil wound on an open-ended core is already dominated by the air path.

Someone enlighten me!

[Cobaltblue]

Messed up quotes.

Please use the preview before posting.

Cheers

Mike T

[Station X]

I've fixed it before it gets propagated in yet more nested quotes which take a lot of work to sort out.

[Andrew2]

Originally Posted by murphyv310

Hi
I'm beginning to agree with the initials of this project.
FSL.... Financial Sinkhole Loop! The cost of the 660/46 Litz is eye watering, ferrite rods are expensive as well.

I've put up a wanted for some 660/46 Litz, would be happy enough to eventually buy more if someone has a spare 15 feet for a reasonable price, so I can try this out with the recommended wire. If it doesn't work out there will be some bargain ferrite rods going.

The wire on mine is just standard insulated 'hookup wire'.

[Radio Wrangler]

You can make your own Litz wire, of course. At least you don't have to sort out and identify the ends of individual strands. Making up hexafilar wire for complex RF transformers was fun at first, but when I started using solvent-based felt tip pens to dye the varnish different colours on individual wires, life became a lot easier.

I've used Litz for making very high Q pot core inductors. I've used it for low loss heavy current windings in SMPS transformers and inductors including some fancy sinewave-output resonant ones.

The price of Litz has always been fearsome. Many times the price per weight of plain varnished magnet wire.

David

[G.Castle]

Originally Posted by murphyv310

A possible source for litz wire is from induction cookers. Not sure of the spec used but perhaps a visit to a recycling centre would be in order.

No reason not to try it, however it is often aluminium wire.

[murphyv310]

Hi.
I've made up a smaller one with 14 rods but added another 14 to increase the length, not glued though. This has increased performance markedly with a noticeable improvement in Q. I'm getting some other wire to try and this will be my final attempt.
I've a number of unused rods so I'll offer them here at the price I paid if there is any interest.

[kalee20]

Originally Posted by Cobaltblue

Messed up quotes.

Please use the preview before posting.

and...

Originally Posted by Station X

I've fixed it before it gets propagated in yet more nested quotes which take a lot of work to sort out.

If that referred to my post, deep apologies both! I thought it was OK, but typing frantically on a mobile phone to get it posted before running out of charge.

This one will be previewed!

[John_BS]

Oh dear. Ferrite rod antennas. Black magic. Electron spin....


How about we use the BHP of the forum to conduct some controlled research?

1. If we take a single rod as the starting point, we can experiment with various coil cofigurations (turns, position, length wire diameter etc) and measure the tuned Q v. all these variables. We've not actually extracted any energy at this point, and the Q is likely to be higher than desirable for AM reception. But once we've made a satisfactory single-rod antenna, it can be used as a reference.

2. I've observed that two rods, tuned to the same frequency, will interact (i.e. couple) over significant distances. Probably the distance is related to the Q of the rods. Quantify this.

3. Construct a simple screened generator loop in order to generate a known H-field and hence allow comparison of the "gain" of the various topologies, removing the vagaries of using an off-air signal.

4. Has anyone attempted to model the multi-rod configuration using existing rod equations, but substituting a value for Ur which corresponds to the mean value formed by the cylindrical pack? (e.g. Urod* X-section ferrite/x-section overall )?
John

[Bazz4CQJ]

Originally Posted by Bazz4CQJ

The biggest advantage the active mag loop has is probably that of being relatively immune to electronic noise. It isn't that the long wires have stopped working, it's simply that they drag in an S8 noise level, which the mag loop does not.

So, are the FSLA immune to electronic noise; if not, I'll pass.

B

That question about noise doesn't seem to have had any answers

B

[murphyv310]

Originally Posted by Bazz4CQJ

That question about noise doesn't seem to have had any answers

B

Hi.
They are better than a long wire but not as good as a magnetic loop.
I made a two valve Regenerative radio last year using two Soviet Rod Pentodes, a scavenged Ferrite rod of 175mm x 15mm using the medium wave coil from the KB donor set and tuning cap, five turns for the feedback winding.
This radio works unbelievably, sensitive and very selective even at minimum reaction. Using a bit of reaction it works just like the Ferrite sleeve loop antennas but even more so, I can then bring another portable close to this radio and get enormous gains and pull in excellent DX, an added single turn on the rod feeds my Xhdata on top band (which the home made set tunes to) and gives excellent results and pull in nets otherwise inaudible.

[murphyv310]

Hi.
I've received some wire from Kalee 20 and this morning early I rewound the existing coil with the new wire. On Wednesday I also decided to make a simple Q multiplier as the straight Ferrite Sleeve Loop Antenna really didn't exhibit that sharpness I anticipated, the first attempt was with a 1J42A Soviet rod valve, the rather rare one whichboperates on 6 to 9v HT. This really improved the Q and resulted with 5v p-p RF on my local on the anode. I couldn't resist adding detection and an AF stage using another 1J42A feeding a pair of high impedance phones. Works very nicely indeed and up to 2mhz, heard those two guys on 1932khz on LSB easily with the regen just oscillating, hand capacitance though is an expected issue.
So I can now feed the RF to my D808 (when it behaves) to give excellent top band results.
Peters wire has improved output on weak stations noticeably.
Here's some pictures of the original rod pentode radio with the thick ferrite rod, it easily drives a speaker with just two valves 1J24B and 1J29B also the latest project.

[murphyv310]

Hi.
Have rewound the coil on brown thick paper around the centre of ferrite rods, this has increased output. Also filling up the tube with ferrite rods gives a small rise in signal.

[Andrew2]

Have you positioned the coupling winding for max smoke? I found the coupling winding on mine (feeding a 50 ohm rx input) was critical - just one turn and almost falling off the end of the former. Too close to the main winding and the Q dropped.

[murphyv310]

Hi Andy.
Yes the single turn needs to be at the edge of the rods I've noticed or it damps the whole thing badly.
The best way though is on the anode of the Q multiplier, to add a toroid with 50 turns and a single 1 turn output winding as an RF transformer, this works beautifully as the feedback for the actual Q multiplier is taken from the valves G2, the extremely rare 1J42A valve is ideal for this type of circuit.

I've also found out that the ferrite rods I'm using are no good for the application, to be fair without the Q multiplier the Q is relatively low and the tuning not all that sharp. This is now as far as I will go with the project unless I can find rods that I don't need to get an overdraft on. I'd like to get a little back on the rods I've already bought that are no longer any use for me.

[kalee20]

I'm interested that the multistrand wire has improved things! Presumably the same number of turns as before?

While higher Q is nice to have, there's a limit in practice as to what the system will cope with. For MW reception (say 1MHz frequency), and audio 3db to 8kHz, the tuned circuit has got to be able to follow the modulation envelope, and this puts the total HF bandwidth at 16kHz.

Using the relationship BW = fc /Q we get maximum Q = 62.5.

The in-circuit Q is the total loss resistance (coil + capacitor + external), the capacitor losses are generally negligible, the circuit and coil not so. If the coil has a Q of 40 then it's a case of 'could do better' and reaction will improve things. If the coil has a Q of 63 then the circuit will have to impose very little loading else reaction may still be necessary. But if the coil has a Q of 300, and it all works with no treble cut, then it's clear that the circuit loading must be the dominant determining factor, and there's nothing to be gained by remaking the coil with super-unobtanium-litz giving a coil Q of 1,000,000 - it'll just be totally diluted by other factors.