Maybe there is a post (or several) regarding this but I have some questions that I would like to share with you:

1. The core of the FSL, has to be foamed or can be just a non conductive cylinder-shaped object? What about PVC?
2. I am interested in NDB and MW band, so my interest would be from 150 to 1750 (more or less). Which kind of variable capacitor do I need? I know it depend on the diameter of the aerial. Maybe a 3" baby loop or even a 5" are suitable for me as a first project. My portables are DEGEN DE1103 and Tecsun PL-330. 
3. Is it possible avoid the variable capacitor adding a pre-amp to get a broadband FSL?

I am thinking to purchase ferrites in the same place where Graham (Maynard) got the ones he used. Any other suggestion?

Thank you very much in advance!

--

Have you checked out any of the construction documents for the various sized FSL the Gary wrote? There are some of them in the files section here under "Antennas and Equipment" (I believe).
I think that there are others online as well. They will not answer some of your specific questions perhaps, but will give you ideas of what is known to work.

I am not sure about PVC. It depends on what kind you use. I have read that the white PVC is the best for coil forming, but it can be lossy at higher frequencies. It could influence the Q of the system. How much at MW? I haven't seen measurements.

With the recommended inductance and variable cap my 7" FSL does not tune much below 500 on the low end. I believe that some people have built multi coil FSLs to get the lower frequencies.
Not sure if I helped, but maybe gave you some ideas for further research.

I am sure that Gary or others here can add  much more info for you.

Phil

Dear Jorge (and all),

Thank you for your interest in FSL antenna construction and operation. A good introductory article for those DXers thinking about using an FSL antenna is posted at https://dxer.ca/articles/92-gary-debock

Since FSL antennas are not currently manufactured commercially, most DXers make their own. A guide to how different construction materials result in different gain performance is posted at https://dreamcrafts.box.com/s/mr7aec2o4fid5u4dc48xz0t6u9uto8xh

There are some specific FSL antenna designs for both Longwave and Medium Wave frequencies, or both. Some FSL antenna designs are posted in our photo section. There are also some construction articles posted in our file section for the 3.5 inch, 5 inch and 7 inch FSL antennas.

FSL antenna materials (especially multiple ferrite bars or rods) are relatively expensive in comparison to cheap wire antennas, so these antennas have always been relatively scarce. Their DXing performance is awesome for their compact size, however, which is why I always use them on ocean coast (and ocean cliff) DXpeditions. Most recently, a tiny 6 inch (15cm) diameter FSL model ran wild in long range Asian MW station reception on the Oregon coast. 

Gary DeBock (in Puyallup, WA, USA)

Sorry that I can't recommend where to get parts in Spain. I suppose ordering from the US would be too costly. I could find the place that I ordered the currently recommended variable capacitor if you would like. It is also documented in the forum here in a few places, including an alternate source.
I found this:
https://m0ukd.com/calculators/resonant-frequency-calculator-inductance-capacitance-lc-circuit/
You can play with values to see what should work. As Gary mentioned, he believes that there is some information on dual coil designs for covering both long wave and medium wave frequencies (in single or separate antennas) in the files/photos section here.
Though, those designs were for larger models of FSL IIRC.

BTW: I found a link to the place I bought the latest recommended air variable cap:
https://www.mikeselectronicparts.com/product/384pf-air-variable-capacitor-with-81-planetary-reduction-drive/


Phil

On Fri, Dec 11, 2020 at 01:23 AM, Jorge Garzón wrote:

Sorry, I wanted to say 5 inches FSL (not 3,5" as I did)

 

Hello Jorge,

Attached is a design photo of an effective 5 inch (12cm) diameter FSL antenna, which provides powerful gain in a compact size. One of these FSL models was recently sent to Paul Walker in Alaska, and he is tracking down lots of long range DX with it.

<<<   1. The core of the FSL, has to be foamed or can be just a non conductive cylinder-shaped object? What about PVC?   >>>

The core of the FSL needs to be a dielectric (insulating) material, and should also be soft enough to provide some protection for fragile ferrite rods or bars. My own FSL models use a PVC frame, with a PVC pipe through the center of the ferrite sleeve, through a rubber plumbing coupler packed with soft pipe insulation and a swimming floatation aid. This kind of FSL design is waterproof, tough and survivable in risky environments like ocean side cliffs. But if you just want to use your FSL in a safe indoor shack, you can use almost any kind of inner core, as long as it is a good insulator.

<<<   2. I am interested in NDB and MW band, so my interest would be from 150 to 1750 (more or less). Which kind of variable capacitor do I need? I know it depend on the diameter of the aerial. Maybe a 3" baby loop or even a 5" are suitable for me as a first project. My portables are DEGEN DE1103 and Tecsun PL-330.    >>>

If you want to keep your FSL antenna compact and relatively lightweight there are some ideal 384 pF variable caps, which provide vernier tuning so that it's easier to peak the antenna's gain boost. But a 384 pF variable cap will not cover the frequency range from 150 kHz to 1750 kHz unless you have separate, switched Longwave and Medium Wave coils. My advice would be to have separate Longwave and Medium Wave FSL antennas with 384 pF variable caps, since there are different types of ideal Litz wire for the two different bands. But there are some larger FSL designs with the LW-MW coverage you desire, although the variable caps will be much larger, and trickier to tune with such a wide frequency range.

<<<   3. Is it possible avoid the variable capacitor adding a pre-amp to get a broadband FSL?   >>>

This type of design was tried back in 2013, but the results were poor. The FSL antenna's effectiveness is related to its High-Q tuned circuit, which optimizes one single frequency very sharply, providing excellent gain for its small size. When you take away this important advantage you are basically left with a mediocre replacement antenna that receives all frequencies poorly.

Gary DeBock (in Puyallup, WA, USA) 

           

On Sat, Dec 12, 2020 at 12:11 AM, Jorge Garzón wrote:

Thanks Gary. I also have the FSL 5" document, full of useful info. 

 

What about ferrite providers? 

Jorge,

If you wish to build a 5" FSL antenna using the same 125mm x 8mm ferrite rods that my design uses, the Russian surplus ferrite rods are available at this link  6 pcs Ferrite Rod NiZn 8 x 125mm for Amateur and Crystal Radio Coils, AM SW USSR | eBay
The seller in the Ukraine says that he only has 5 lots of 6 rods available, but he typically lists more identical rods immediately after these are sold.

Gary

On Fri, Dec 18, 2020 at 02:21 AM, Jorge Garzón wrote:

Well, I have ordered whatever I need for my 5" inches FSL but the Litz wire. Jist a question... Do I need 40 inches or 40 feet. I am not used to imperial units system and I do not want to get confused with 'inches', 'feet' or their symbols like ' " etc...

Stay healthy!

J

Hello Again Jorge,

40 feet (12.2m) of Litz wire will be enough to wind the coil on a 5 inch (12.7cm) diameter FSL antenna.
It will actually be enough to wind the coil for almost any diameter of FSL antenna, since the smaller FSL's simply have more coil turns to result in the same approximate inductance.

One important thing to remember is that proper tinning and soldering of 1162/46 Litz wire requires a very hot soldering iron or gun, with at least 60 watts of power. This is necessary to thoroughly melt the solder throughout each individual Litz wire strand on both ends of the coil. This process generates quite a lot of unhealthy solder smoke, so it's best to do this soldering outside your house, with a fan to blow the smoke away as you make the connections.

73, Gary

  

Hi,
Well, now I am assembling my new FSL antenna. Finally will be 4" as the PVC tube that I found was 75mm wide. I changed slightly the supporting structure as I prefer to avoid PVC and favour wood. I will also use a wood circle base which is rotatable and can get the azimuth more easily.

I am still waiting for the Litz wire. I ordered 50" and I will use 40" to be winded on the antenna. Is that right, Gary?

I am attaching a picture to show how is going!
73 y buen DX

--

Nice work, I will be keen to see how this goes for you.

Paul
https://ultralightradiodxing.blogspot.com/

On Sun, Mar 28, 2021 at 12:12 AM, Jorge Garzón wrote:

I am still waiting for the Litz wire. I ordered 50" and I will use 40" to be winded on the antenna. Is that right, Gary?

Hello Jorge,

As long as 50" means 50 feet, and 40" means 40 feet, you will be fine with those lengths! I know that inches are not used in Spain, so I'm pretty sure that you meant "feet" instead of inches.

Since FSL antennas have become very popular around the world I've tried to switch all my own measurements over to metric, but since American stores still sell measuring tools with the old system, it's a challenge! :-)

Thanks for your photo-- it looks great!

73, Gary