On Tue, Feb 28, 2023 at 09:15 PM, John Stein wrote:

There is NO free lunch!!

Well, in all credit to you John, at least you tried it, and reported back to the group.

Stuff like this is always a worthwhile learning exercise, and often takes you off in a different direction, where you may discover something else in the process.

Most excellent (to quote Mr Burns)

Regards,

Martin

When something is posted in Files, the only way to view it is to download it.

If you have not put a description, if I have to download a file to look at it to tell what it is, I'm deleting it. There are too many JPGs in there with only a date code as a name with no or only a cryptic description. I'm deleting them.

Think about someone going into Files or Photos a few years from now, not having your emails discussing it in mind. Will they know what it is based on the file name and description? Is it useful for them?

Files and photos not in folders are a bit like going to a common meeting space, throwing pictures and little bits of stuff everywhere, then just leaving it for someone else to figure out and clean up. It is rude and inconsiderate.

If you only need to share a file temporarily, consider posting it on a file sharing site and putting the link in your message.

Thank you,
--
Steve Greenfield AE7HD

What do you mean by tried to post? The list does not allow attachments, you must post them in the Files section. Preferably in a folder with an appropriate name.

Think about someone looking in the Files section a year or two from now, will the know what your file is, based on the name and description? Without reading the posts related to it?

I'm about to go ion there and delete a lot of files that have no or insufficient description.

--
Steve Greenfield AE7HD

How much room do you have???

There is NO free lunch!!

To verify the presence or absence of coupling between the two co-planar resonant loops, I mounted two spiral-wound loops "edge-to-edge".? Loop "A" was resonant at the frequency of the incident radio signal.and drove the receiver via a one-turn coupling loop.? The second loop (Loop "B") drove a dummy load via its coupling loop.? The resonant frequency of Loop "B" was adjusted while observing the signal level indicated on the receiver "S" meter, The received signal dropped as the resonant frequency of Loop "B" approached that of Loop "A", indicating the presence of significant magnetic coupling between the two loops when at a common resonant frequency.? After a little thought, I realized that I had built a grid-dip meter!

While the existance of this coupling invalidated my proposed two-loop scheme, in the interest of completeness I then connected the coupling loop of Loop "B" in series with that of Loop "A" and observed the receiver "S" meter as the position of Loop "B" in relation to Loop "A" was varied.? The best I could do was an indicated signal level equal to that with Loop "A" alone connected to the receiver.? Any other position or rotation of Loop "B" resulted in lower signal.??

Unfortunately, I do not have enough room to locate the two loops far enough apart to eliminate the magnetic coupling, so the approach of using an array of widely-spaced loops and a phase aligning network is out of the question for my case.

Thanks to all for their comments and recommendations

John

On Tue, Feb 28, 2023 at 12:47 PM, John Stein wrote:

I live less than 2 km from the antenna array for a 50 kW broadcast station,

A high Q series tuned notch connected across the receiver input is one method to reduce the signal level of unwanted broadcast stations. Alternatively a high Q parallel tuned (wave trap) circuit in series with the loop input to a broadband loop amplifier is another method, but this only really works on the lower frequency bands, where the loop feedpoint impedance is very low.

With receive antennas it's all about the Signal to Noise performance, and beyond a certain level of performance, you can really only improve the Signal to Noise ratio by introducing some form of directivity, in order to reject unwanted signals and noise as much as possible and just focus on the wanted signal.

Apart from their use when transmitting, tuned loops don't offer any major advantages over broadband active untuned loops. Plus being low Q you can place several broadband loops fairly close together, and then lobe / null steer the directivity to obtain better overall Signal to Noise performance.

Regards,

Martin

Thanks for your replies.? The issue of the two loops coupling to each other had not occurred to me, definitely food for thought, if I breadboard the scheme I'll make this spacing adjustable.

As far as the untuned loop / resonant loop issue is concerned, I live less than 2 km from the antenna array for a 50 kW broadcast station, so I see the resonant loop as a way to keep this signal out of the receiver's front end.? Receiver is an FRG-7 or a Gonset G66, neither of which has robust filtering at its front end.

Hi

I think you are possibly wasting your time, But hey give it a go! Looking forward to your results.

Phased set of active loops does work however..

Ie read lz1aq delay line…

I have it working here..4 switchable directions from in shack..

Maybe a pic posted if it goes through on here..( though you can only see 2 of the 3 loops.)


Simon g0zen

开云体育

John

A number of tuned loops connected together would not sum as you describe, it would be a vector sum that would be very dependant on having every loop exactly tuned to the same frequency so that the phases of each loop would be similar. If the loops were in the same plane and the Q was high then they would need to be wide-spaced. This would be a very large structure as a spacing of at least 2 diameters between centres would be desirable with Q=10, the spacing would need to be much greater with Q=100 loops. You could produce N times the power which would give root N voltage into a N times matched load however paralleling the outputs into a matching transformer would be much more desirable than series connections.

Above around 5MHz a single tuned loop should reach the local noise floor on any site,? so adding many other tuned loops together would not significantly improve the S+N/N ratio but it would be very difficult to track-tune. As it is tuned loops don't integrate with modern multichannel SDR's, apart from measuring noise levels tuned loops are not very useful at all, a modern single turn active loop can easily work very well for 100KHz to 30MHz reception, will have very stable gain and feed very many SDR's on many different frequencies.

At MW? a tuned loop does not produce a significantly better S+N/N than a good quality active loop in an urban environment but it has the huge advantage of not needing tuning.

Using good quality aperiodic active loops is a worthwhile project in order to do beam forming or to notch some directions to minimise QRM, the commercial/military units are often resistively loaded cardioid units. Aperiodic units can be much more closely spaced than tuned loops.

Such directional arrays were described by CS Antennas in the UK around 40 years back but there are US manufacturers too.

It is possible to directly connect several loops together and then tune them all with a single capacitor, that has some advantage but the multiple connected loops work even better as an active broadband antenna.

Four square loops connected directly together is a well known arrangement, it is only beneficial in very quiet locations. The 4 times area does produce double the voltage and it has about a quarter of the inductance of a single loop.

A two loop arrangement with one above the other needs one loop to be reversed to sum the loops. I did experiment with such a loop as a tuned arrangement, something quite well known by loop experimenters, the two loops only need one tuning capacitor. You could make a four, five , six or more loop arrangement so that the loops are co-planar and tuned by a single variable capacitor, that is another known arrangement but it really is overcomplicating a simple loop for urban QRM levels.

Regards, Alan G8LCO

开云体育

--
Steve Greenfield AE7HD

good luck
still to cold here to mess with antennas yet? ?but pre planning some small tower stuff for the six meter cycle coming.
73
Murf

Ah also,

The tuned loops are higher Q than broadband loops and they will interact. I have experimented with two tuned loops parallel to each other, and only one needed to actually be fed, as there was sufficient mutual coupling between the two over quite a large distance.

If you do use them like this, they may need to be mounted 'end on' to each other in order to minimise any mutual coupling, or simply use one fed loop and several parallel separately tuned loops that are just passively coupled.

Regards,

Martin

I think you may encounter some problems with the physical spacing and the feeds simply being connected in series. However a similar technique is used a lot with active broadband loops, so in theory it should work with tuned loops too.

I suspect that you may need to passively combine them, but via suitably phased lengths of coax, so that the signals from each loop arrive concurrently and add in phase. The other issue is ensuring that each loop is tuned to pretty much the same frequency, or once again you will have phase problems.

So yes I think it could be made to work, but there may be additional complexities that need to be sorted out.

Regards,

Martin

Good afternoon all,

Has anyone had experience with stacking multiple relatively-small tuned loops as a means for increasing the effective height of the resulting array without violating the assumption of uniform current in each of the loops' windings???

What I propose is a set of "n" resonant loops, each having a total winding length of one-tenth lambda to satisfy the uniform-current constraint.? Each loop would incorporate a single-turn coupling loop with the "n" coupling loops connected in series.? The array output would be taken from the endpoints of the series connected set of coupling loops.?

Assuming the plane of the incident radio wavefront and the "stack" of loops were parallel, the currents in each of the coupling loops would be in phase and the voltages appearing across each of the coupling loops would combine as scalars.? The resulting array output voltage would be "n" times that of each individual loop, implying an increase in effective height by "n".

Comments please.? Does this make sense?? Am I missing something??

thank you,

John