Alan,

Thanks for the time you spent on your extensive write up. Much appreciated.

To answer your questions/advices :

1. There is a steel reinforced concrete floor between the Baby Loop and the floor below. I do think that takes care of one of your concerns.
2. The PA will be 500 Watt, not 2Kw
3. It is impossible for anybody to touch the baby loop. The lowest part of the baby loop is 3.5 meter above the floor level of the roof.
4. At two side of the platform there is nothing.. It is at a corner of my apartment building.. The ground is 5 floor lower. roughly 15 meters.
5. The place the 1.5 meter high platform is build is 5 meters away from the patio wall with the neighbors. They will require to get first a ladder to get over the wall before entering my? ? ? ?
? ? patio. By doing this they would be unlawful entering my premisses.? But even then they can't touch the aerial because it is 3.5 meter high
6. I have no kids anymore at home. Both my kids are studying at university.

I think from a safety perspective I am ok. The manufacturer recommendation says 5 meter distance and I do comply to that.?
In addition 3000 of these baby loops have been sold and I have not been reading one incident with them.??
Lots of HAM radio amateurs are installing them in a far more compromised safety way. Like in-house or on a small balcony.?

I hope I have replied to your concerns. But I do want to thank you for the time you took to warn me. That is really appreciated.

73, Frans

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Not so much a propagation concern as keeping the near fields away from people. The voltage on the tuning capacitor will be of the order of many kilovolts? with a current of >10 Amps at around the 100W level. Any antenna is a transducer that converts electrical energy into electromagnetic energy. A resonant wire dipole can be very close? to 100 % efficient.? A good transmitting loop can also be efficient but the much smaller structure needs much higher E and H fields to radiate so the near field intensities are very much higher than a full sized antenna.

?A continuous screen over a roof would reduce the exposure to people underneath the loop. If it is a concrete and rebar structure there may be no connectivity between the rebar so there may be no screening for people a metre under the roof mounted loop.

Fitting a loop to a fence also implies that people on the other side of the fence can receive?? very high exposure without understanding the risks. You cannot protect children, babies or pets on the other side of the fence. So Cirro's? reply is easy to understand.

As? there are now? requirements to assess fields around transmit antennas it would be prudent to follow the recommendations. Personally I would want to keep at least 10m. away from a transmitting loop radiating 100W . Putting 2 KW into a loop puts over 4.5 times the current and voltage into the structure compared with 100 W operation. That would be enough to arc capacitors and generate huge RFI in many loops however the Cirro loops have exceptionally high power ratings with 14mm minimal capacitor plate spacings.But then the E and H fields are very high, don't worry about objects or lengths of cable- think about People and your humanitarian and legal position.

Wet trees are not that lossy, signals do not vanish when it rains even though a ground wave signal can go through hundreds of trees. Rainwater is quite pure and forms a very thin partial film on trees. Sap is a much greater attenuator potentially as it has a much larger cross section however it's not much of a problem to LF to VHF radio waves. People have used trees as transmitting antennas, not nearly as good as? 35m of metal mast but a lot cheaper. Trees have a very long history as supports for wire antennas, people don't complain about the tree getting warm but are happy to get the wire into the air.

Now that there is a requirement to consider the exposure of others in some Countries I would not ignore this need, a vexatious? group could cause a lot of trouble,? demonstrating compliance is a valuable defence and a wise precaution. Position matters.

73, Alan G8LCO.

I not put anything near the loop. I would only build something below the loop. A platform of 1.5 high where the 2 meter pool is standing on. And then the loop will sit on the pool.?
The loop will then be 3.5 meter high from the floor space of the patio.??

Steve, Thanks for your long response. On the rain. Yes I was reading about this. The manufacturer even recently modified one model by adding a cover on top of the capacitor because rain got too much influence. But the babyloop is still original. But luckily I am living in Lima Peru and it simple doesn't rain there. It seldom drizzles.?

On the location : I not have an option to put in on the ground because I life 5 high on a top floor.?
The only option is to put it direct on the balcony instead first build a little platform. We luckily have 104 meters of free space on the top floor (a kind of penthouse) and the back patio is something we anyhow not often use. The platform I think need to be build, because at the back patio there is a wall of approx 1.8 surrounding at 3 sides. And at the 4th side one of my rooms looking towards that patio. That room is 3 meters high. I If then not build a platform the loop would be blowing directly into that room... I need to be above that room.. that is why i want to build that platform... for which I need to know the dimensions...

I am putting in on my own part of the roof. That is a penthouse. Nobody has access to it unless on purpose my neighbour climes over the wall which separate his and my appartment.?
And it is to top of a 2 meters pole which is again 1.5 meters high. I think this is safe. But thanks for the warning.

And definitely don't located in a place where people can touch it. The voltages on any transmitting loop can be astronomical and possibly lethal. As a teen I put up a loop on the back porch. My mom was hanging out laundry to dry and accidently brushed up against it. It was almost lethal for me when she came back into the house. :-)

You may better understand things from my perspective, if you take a look towards the bottom of this webpage.



Regards,

Martin

The other problem in the UK (and the USA too) is trying to comply with OFCOM RF exposure limits, which is especially problematic with efficient tuned loop antennas.

Folks usually can get away with home built, or even commercial designs, because they have so many lossy parts or don't have a very high power rating so they don't pose much of a risk.

However, once you start to use a properly engineered and efficient loop, things can become quite dangerous.

In this case I'd agree that it's definitely worthwhile considering a calculation of the exposure limits and suitable safety zone distances from the antenna when it is in use.

Regards,

Martin

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On Mon, Feb 13, 2023 at 02:12 PM, Tom Seeger wrote:

https://chameleonantenna.com/shop-here/ols/products/cha-rxl-pro

Personally I still wouldn't buy one from them for all sorts of reasons, some technical and some ethical.

Chavdar, LZ1AQ, was good enough to openly publish his design and related information free of charge, so that folks could build one for themselves. He also sells ready built amplifiers at about 1/4 of the cost of this unit.

I wouldn't like another company to profit from my, or anyone else's hard work, or at least not without some form of acknowledgement or financial contribution made to the originator. My experience is that this company tends to simply copy designs, usually without fully understanding how they work.

Regards,

Martin

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I would think any material you add near the loop makes things worse. My understanding of the manual is that the loop should be 1.5m away from other objects.

73, Mike AF7KR

If you look very closely at the picture of the PCB in their ad, you can clearly see that the circuit has now been changed to an LZ1AQ version. I guess after Steve's poor review of the original, they made a major change. :-) Tom
https://chameleonantenna.com/shop-here/ols/products/cha-rxl-pro

I have to reply on this - the unit looks nice, but I have to also agree that for $525USD, you can get a LOT of loop with more flexibility.?

I am currently using the Wellbrook ALA-100LN-M. This unit is optimized for/uses a wire antenna, but the amp is highly adaptable to wires, copper tubing, "fat cage" style elements, and even larger loops. According to Andy Ikin, the ALA100 will have a pretty flat antenna facot with a ~4m loop perimeter. If you have a need to listen in certain bands, you can adapt the perimeter to that application. I made a 4.8m "hex loop" style wire antenna using flexweave. Works superbly, and very low noise. Use of a CMC (choke) using RG318U around 2.5" cores will also aid in reduction of local noise when used inline of the feed cable. Depending on the region of interest, cores can be 78/31 (two in series with 35t each) for low band to LF. or 43/31 cores for MW top of band to HF. There are lots of articles on CMC chokes, and I won't cover here since these can be made for taste, and will run less than $40-50 total.?

The ALA is just over 1/2 the price of the CHA Pro, and can be set up even as a mobius style (tons of fun to be had playing) - the other choices offered are also excellent. I use a CCW Front end unit (isolation XFMR) on the output of the PSU/bias Tee to my SDR. Very low loss there. 20-25W NDBs over 1800 km away even with distant T-storms are audible (solid copy) in the 800-1100Hz BW range! So these work well indeed.?

My loop is fixed currently in the ESE-WNW orientation for convenience, and Caribbean/S American MWDX is fairly routine, as is SPac SW DX. Noise floor is excellent and these handle very high levels of MW fields without significant spurs. (Have over 3x50kW stations within 30km, a few 25 and 10kW stn closer).

This loop can be made "stealth" too for those with HOA restrictions so lots of options.?

With the adaptability of these type of wire loops, and their performance, they are tough to beat!?

Good luck!?

Darren
VE4VE


--
Darren Hennig - VE4VE -?Winnipeg MB Canada. 49.97N/97.07W; EN19lv
Running: *Elad DUOr Receiver, *Elad FDM-S2 Software,?4.84m Hexagonal Loop?on Wellbrook ALA-100LN-M. (Main-external)
Ancillary: CommRadio CR-1a/Icom R-75 with 140mm dia. FSA, 150mm long, WellBrook ALA-1530 (Indoor).?
Audio processing: West Mountain Radio CLRdsp unit. (When SDR is stand alone); TASCAM AR-1 recorder/Sangean digital recorder.

Don't buy it.

In my opinion the price alone should stop anyone buying. I know they have to make a profit..but $500 plus! Atleast the mla30 ( rubbish) is only $30 or so. Or a ccw loop much much better than mla30. Comes complete circa $150?? ( look for the twin loop one on cross country wireless website.)

One can get a welbrook for less military, gov’s etc use) . Or order a Lz1aq preamp from Chavdar and make your own loop.

Or even just make your own preamp, but I know not everyone wishes to do so.

Just my opinion.. $500!

Simon g0zen

Posted by a well known member of this group...

/g/loopantennas/message/14907?p=%2C%2C%2C20%2C0%2C0%2C0%3A%3ACreated%2C%2Cchameleon%2C20%2C1%2C0%2C83874875

Roger

Thanks.

I need to build a platform on top of my apartment building to get 360 degrees clean space for my new babyloop.?
My babyloop is a 1 meter loop.

The platform will be at the corner of the building. It will be 1.5 meter high from my roof deck.
But at two sides of the corner it will be 5 floors from the ground floor which is roughly 15 meters.
On top of that platform I will then install an 2 meters mast and on top of that the babyloop.

The instruction of the babyloop states that you need to have a flat surface below the babyloop.
But it only states the height the babyloop needs to be installed from the flat surface (minimum 1.5 meter and max 2.5 meters.
It however does not state what the dimensions should be off the flat surface? (the platform I am building).?

Can I assume that if I install the babyloop exactly at the middle of the platform that the dimensions can be 1x1 meter square ??

Oh

I also forgot to ask

Looking for a design for a 1:1 isolation transformer Qro from 160-40m..

Have 2 240-61 cores suitable but not sure on amount of L to wind on.( ptfe silver plated wire)

Thanks