PE-Xc/Al/PE-Xc aka PEx/Al/PEx the New Copper?

Wanting to build a low profile mono-band antenna, I looked into the old design by J.M. Boyer (U.S. Patent 3,151,328). The DDRR-antenna, as originally designed, i.e. about a quarter wave circumference, allegedly as a rather narrow bandwidth.
There is another variant out there, which is said to got a wider bandwidth. This design asks for a half wave circumference, which the advantage of having a closed loop (less noise!) and no need for an expensive capacitor.

OK, that's a plan, let's think of a DDRR for my flat root top. This antenna would be entirely invisible from the street.
But, what about the B.o.M. (Bill of Materials)? Well, a neat design would call for about 21.34m of soft copper tubing having a 10mm diameter. Well, the stuff exists, however, however, a 25m roll of 12mm soft copper tubing would cost about €185.- presently. Well... that's a bit too stiff or my taste!

The hardware store had also 5m rolls of 12mm copper tubing for about €30.
OK, we are coming closer, I would need to buy 2 such rolls and an additional piece of piping, in order to build a quarter wave DDRR antenna. But, I would need to think of a (variable) capacitor.
Nothing of interest, I decided, and left this particular store.

Next store, maybe their copper prices are lower... no, there were not! However, I noticed some other stuff, which the first store did not sell. The stuff is called PE-Xc/Al/PE-Xc, aka PEx/Al/PEx.
What is that?!

• PE-Xc or PEx stands for "cross-linked Poly-Ethylene"

Hugh, you might think, is he gone crazy? Building an antenna from PET, the stuff of which fizzy drink bottles are made of?
Well, there is this other material in the and ....

• Al stands for Aluminium (Aluminum)

The PE-Xc/Al/PE-Xc-stuff is a tubing material made from an Aluminium layer sandwiched between 2 poly-ethylene layers. The interesting bit about this Aluminium layer is that it is supposed to be an Oxygen barrier (cf. wiki) and is therefore sealed by welding (according to many manufacturers).

14mm PE-Xc/Al/PE-Xc

Right, now we know that the PEx/Al/PEx stuff can be interesting for building antennae.

Also good to know, the stuff is very lightweight, compared to Copper tubing. Not only is Aluminium one of the lighter materials, the Poly-Ethylene makes the stuff really tough (10bar of pressure at 95C), such that the metal layer can be much thinner. Mind you, in radio frequency, we are only interested in the most outer diameter of the metal, thanks to the skin-effect.

The price? Alright, time to talk money. I bought a 10m roll of 14mm PEx/Al/PEx for just under €30. Only half the price of Cu-tubing?! Is that worth it? Well, the costs are not hidden in the materials for PEx/Al/PEx, since, a 10m roll of 20mm tubing, the largest diameter this particular store had in stick, is only €35.

Enough about the material itself, you'll find plenty of information about it on the interweb!

A material so light-weight and still stiff calls for designs like hair-needle antennae and alike.

Pretty novel, I thought... NO it is not! There is one design disclosed in the interweb, which makes use of PEx/Al/PEx in a magnetic loop / frame antenna cross-over. Have a look at the "2 TURN LOOP ANTENNA".
What I like about this design is that no electrical connection is made to the Aluminium layer. Why? Aluminium is not exactly a noble metal. Any connection with a metal other than Aluminium may cause problems, one or the other way.

Along those lines, how would one possible connect a capacitor to the Al-layer? Well, that is, considered the dimensions, actually pretty simple. Have a look at the images below, they may look disturbing. And yes, this is pretty ghetto!

RG-213 meats PE-Xc/Al/PE-Xc

close up

And here is where the capacitor resides, between the Al-layer of the PEx-Al tubing and the braid of the RG-213. Of course, the braid of the 213 is made from Copper, however, the is no Galvanic connection between those metals, and hence, no corrosion!
Although the RG-213 fits into the PEx-Al tubing nicely, there is some friction... and that is good!


Ideas

1. Building a magnetic loop from the materials shown above.
   A single turn loop made from PEx-Al with a length of RG-213 inserted into both ends of the loop symmetrically. The loop will be tuned by widen or closing it other the inserted length of RG-213, actually acting like a butterfly-capacitor. I will aim for about 14.070MHz. Once tuned, I will tape up the loop endings in order to lock tuning and prevent moisture to enter into the tubing.
2. Building a quarter wave DDRR, as intended in the first place.
   Similarly to the magnetic loop above, the capacitor will be formed by RG-213 inserted into the PEx/Al tubing. However, there is a problem with the ground connection of the loop! The present idea is to remove the outer PE layer, wrap the Al-layer with Al-foil and clamp this down with a hose clamp. Of course, the Al-foil will corrode, hence, it will have to be replace occasionally.
3. Building a frame antenna.
   This essentially means to coil up a good part of the PEx/Al to a decent pack, having a coupling toroid in the center winding. This technique, you might have seen at various antennae I published before, e.g. OctaPlumb (different plumbing material though).
4. Different PEx/Al tubings might fit into one-another, forming capacitive couplings.
5. I can imagine using PEx/Al with INOX-screws connecting various coils thereby, together with capacitors as disclosed above, forming traps.
6. The PEx/Al tubing might potentially be usable for shielding a loop made from RG-213. Insert theRG-213 into the tubing, both end peaking out. Solder things down at the "far end" of the loop and slide the far end to the tubing... Follow your imagination for the rest!

Conclusions
First, I had in mind building a DDRR-antenna. However, seen the possible simplicity, I may build a magnetic loop first.

Post Scriptum
It seems that the PE-Xc/Al/PE-Xc, best suitable for amateur radio, is found under "floor heating".

H-Probe (the Aerial Formerly Known As Shielded Loop)

Short update, not only the name changed, some more happend.
Parts are collected, the TL592 based amplifier should be done in minutes.
The shielded loop is past now, I will reorganise the inside of the tuning-box. The toroid is removed, coupling will be done at the high impedance region of the loop, i.e. at the tuning capacitor.

Oh, should you wonder about the new name, this contraption is near to entirely screened, any E-field should therefore essentially be excluded from detection. A magnetic field, or H-field, will induce a current in the loop. This current will peak at the resonance frequency, creating a high impedance RF signal across the tuning capacitor. The aerial therefore probes the H-field, hence the new name.

Shielded Loop (some photographs)

No new development yet. Here are some photographs to help the imagination. The loops will be provided with some amplifiers soon-ish.

There seems to be a rule of thumb for the dimensions:
Loop Diameters [cm] = Wavelength [m]
(e.g. 30cm loop diameter for a 10MHz loop)  :-))

For more information on materials and dimensions, please use the label "shielded" down below.

The loops for 30m and 40m.

The gap in the shield, opposite the capacitor.

The capacitor and coupling "box".

Shielded 30m RX-loop

Did some cutting and soldering. With measures like "Pi mal Daumen" and a look at the previous shielded loop (resonanting between 49m and 40m, remember?), I managed to arrive at a shielded magnetic loop resonating at 30m. Diameter is about 30cm, I will however publish more precice values soon. Same materials used, some polystyrol vari-cap. Coupling done with a T37-6.
The loop receives, levels, however, are very low, as expected.

Next step, a preamp. Not sure what design to choose.

RX Loop Experiments

Remember, some months ago I experimented with stuff called "YMVK-as 2x2.5mm²", which is doubly shielded underground mains cable - pretty sturdy stuff (expensive too)!

To that time, I cut a length of about 1.7m, connected one blue and one brown insulated lead to form a shielded double loop. Reception results were pretty amazing (see earlier post - tagged "aerial").

Today, I gave it some more testing, replaced the capacitor with a polystyrene varicap in butterfly configuration, in order to make the spindle neutral; that makes it easier to experiment with the thing.

As mentioned in the earlier posting, seems that the natural resonance of the shielded double loop is somewhere just above 7.4MHz. The capacitor, when resonating the loop to 7.0MHz, measures (MFJ-269Pro) 28pF. Bringing the resonance all the way down to the bottom results in about 5.8MHz at 62pF. Now I've got my numbers.

So, with the numbers all collected, it's hands on a piece of paper, pencil included, and maybe, by the end of the day, there is something to report about a self-resonant shielded RX-loop for 30m band.

The actual plan for the particular, above mentioned, loop is not to cut it down, but leave it just the way it is. This RX-loop, with such a capacitor seems ideal for a 40m QRSS grabber, whenever said band will be activated (volunteers?). Next to that application, the loop also covers the 49m and 41m BC bands, a hand full of underground beacons, the 45m pirate band and the RFID "medium frequency" at 6.78MHz.

Shielded receiving loop

A first experimental setup of a shielded receiving loop. The material is called YMVK-as 2x2.5mm². The diameter of the loop is 55cm. This particular setup resonates between 2.5MHz and 7.4MHz.