On Thu, May 19, 2022 at 09:21 AM, martinbradford2001 wrote:

I came across an article that gave glowing reports of the concept of a non-directional antenna constructed by linking two loops at right angles to each other. The author had built his own pre-amp that was claimed to work well with the two loops in parallel.

Assuming two identical loops mounted on the same axis at right angles to each other.

One facing North - South the other East - West

If connected in parallel, and the North and East ends of the loops are in the same phase, you will get a composite pattern facing North East and South West. There will be a null but not as well defined as with a single loop. Likewise if you swap the phase of one of the loops you will then get a composite pattern facing North West and South East. This is how some loops obtain switched directions.

Here's one example using this technique.

https://reuter-elektronik.com/html/rla4.html

If you can continuously adjust the phase and amplitude relationship (vector synthesis) between the two loops, you can obtain a continuously variable pattern. A bit like the SDR Play Duo, which provides this function in the associated SDR Uno software.

If you add a broadband vertical antenna with the correct phase and amplitude, you produce a cardioid pattern, which resolves the directional ambiguity and gives even further directivity.

Other than 'twisting' the loop, or loosely coupling another antenna into the loop in order to reduce the null, the only genuine way to obtain an omni-directional pattern from two loops at right angles is to use a 90 degree phase shift network. This will produce a clockwise or anti-clockwise polarised omni pattern, depending upon the phase relationship of the loops.

I have a compact CSA crossed loop array that was originally part of a Racal HF DF system. This could be switched between N-S, E-W, circular clockwise and circular anti-clockwise. It utilises two loop amplifiers, a passive 90 degree hybrid and separate switching board using PIN diodes.

My plan is to upgrade the electronics and switching system and add a vertical, so that becomes a steerable wide band HF antenna.

Something like this design from Arris. https://www.alarisantennas.com/products/df-a0115-high-sensitivity-direction-finding-antenna/



Regards,

Martin

That's right.

The second loop is closed.

The feed point is on the bottom corner of the first loop closest to the second loop.

Often it's best to look for the simplest solution. I've seen and tested so many loop designs that are over-complicated!

Regards,

Chris

So I just keep the second loop closed? Too good to be true! I'll get an order in tomorrow!

Many thanks

OK, I've modelled the corner fence antenna as the last job before my break.

I've modelled two 1m square loops at 90 degrees to each other with the lowest part of the loop 0.5 m above ground

The spacing between the nearest sides of the loops is 0.1m but it's not critical.

Now the interesting thing about this antenna that it works perfectly as a NVIS omni-directional antenna if you just connect the LAA++ to one of the loops at the bottom corner closest to the fence corner.

The other loop is close coupled to the fed loop and fills in the usual nulls from a single loop.

No fancy feed arrangements or transmission line wizardry are needed, the loops couple together to make an omnidirectional pattern.

The pattern starts to become oval rather than circular at 28 MHz but it would still be useable at 50 MHz.

Regards,

Chris

I've made a quick web search trying to find it.

Most antennas like this are crossed loop antennas where the two loops sit inside each other separated by 90 degrees.

They are fed at the bottom to make an omni-directional antenna ideal for NVIS work.

The idea of separating each loop out to fit on fence panels at 90 degrees is interesting but how are they fed?

Feeding them half way up each loop may not give the omni-directional pattern that is expected.

As the loops are not centred around the same point there will be phase differences between the loops depending on the direction of the incoming wavefront which will be more pronounced at higher frequencies.

If I can make some time this evening I'll try modelling the antenna and figure out if it works as expected and where to connect the LAA++.

Regards,

Chris

Hi

It does work, best if on same axis pole to keep leads from loop to preamp tiny/ non existent.

But it does mean no null..

Simon

Ps very similar to antennas seen on rv’s..

It's not a loop configuration I have tested but it sounds like a useful one to try.

Have you got a link to the article or web page about it?

I won't have time to try it before my break but I'm sure some of the keen enthusiasts who lurk on here would love to try it!

Regards,

Chris

thanks, Chris...

A supplementary question, if I may... I've been doing some internet research into small untuned receive loops and I came across an article that gave glowing reports of the concept of a non-directional antenna constructed by linking two loops at right angles to each other. The author had built his own pre-amp that was claimed to work well with the two loops in parallel. Do you have any experience of or opinions of the feasibility of using your LAA++ in this configuration? I really don't want to install any kind or rotator. 

My current plan is to install a loop of about 1m diameter made of fairly thin wire stapled to a garden fence. This would get it about as far as possible from any house or electronics and would be fairly unobtrusive. I would put it in the corner of the garden where two fences meet at right angles - the second loop could be stapled to the other fence - at right angles to the first, close together but not concentric - is that likely to work? 

Regards

Martin (G8FXC)

We are making regular weekly batches of the LAA++ so usually it's a couple of days from receipt of order to dispatch.

I'm off on holiday next week for a week so any orders received will be shipped on Tuesday 31 May.

Regards,

Chris

what is the delivery time like at the moment?

Martin G8FXC