The antenna is described at http://chameleonantenna.com/CHA%20P-LOOP%202.0/CHA%20P-LOOP%202.0.html.
This analysis does not consider the proprietary Power Compensator option for lack of sufficient information.
The loop itself appears to be LMR400 coax or similar (nominally 8.0mm outer conductor diameter) in a rough circle of 34″ (0.863m) diameter.
Little information is given of the internals, but the promotional material gives a VSWR curve for a matched antenna at 7.15MHz. To their credit, they give the height above ground and ground type for their tests, though elevation above ground was between 1/2 diameter to a full diameter of the P-LOOP 2.0 is a little vague.
Basic loop (34″)
The VSWR=3 bandwidth scaled from the graph is 27.0kHz. The shape of the curve near minimum suggests that were the scan points sufficiently close, the minimum VSWR would be very close to 1.0 and it is taken as 1.0.
If we assume for a moment that the VSWR measurement was captured at a substantial height above ground, its behaviour approaches that of the antenna in free space. Taking the assumption that the published curve is similar to the antenna in free space, we can estimate the gain and efficiency based on earlier assumptions. Continue reading CHA P-Loop 2.0 small transmitting loop
Having just written again on skin effect and copper clad steel (CCS) conductors on HF, and the potential for less than copper performance, it was interesting to note a thread on QRZ where the OP asked for advice on the issue with budget CCS RG-11.
Two late posts as I write this were:
There really is no real issue with skin effect on HF bands with copper clad materials.
At 1.8 MHz, the skin depth in copper is 0.654 micro-meters (.0000654 mm), so the copper cladding on the center conductor of most RG-11 type coaxial cables is more than sufficient for any of our current bands.
(Stewart 1999) published a set of measurements of the popular Wireman windowed ladder line products. His measurements were in the range 50-150MHz. They form the basis for most calculators on quantitative analyses at HF, despite the fact that it is a dangerous extrapolation for CCS construction.
Nevertheless, the directly stated measurements at 50MHz are a useful calibration point for reconciliation.
Above is Table 1 from Stewart, it sets out measurements of four Wireman m.products and a plain copper line.
A model for current distribution in a conductor is that for a homogenous conducting half space with surface current parallel to the interface. Current density at depth d is given by the expression J=Js*e^(-(1+j)*d/δ) where δ is the skin depth (δ=(ω*µ*σ)^0.5, σ is the conductivity).
Copper round conductor – 1.024mm (#18) single core
A correspondent recently wrote regarding the theory expounded in (Findling et al 2012), and their measurements and performance predictions of the AlexLoop Walkham, Portable Magnetic Loop Antenna by PY1AHD.
The authors give a formula for lossless Q (to mean no loss other than by radiation) without explanation or justification.
The formula is wrong, possibly a result of slavish acceptance of Hart’s two factor incorrectly applied (see Duffy 2015, and Antennas and Q). This error feeds into an optimistic estimate of antenna efficiency.
Analysis of measurement data
(Findling et al 2012) presents a table of measured half power bandwidth for the Alexloop.
Taking the 40m case, lets calculate to Q for a lossless loop, Qrad in Findling’s terms.
The roller inductor in a Palstar AT2K will be taken as an example to illustrate the technique. This tuner is popular and has a very good reputation amongst hams, though (Duffy 2012 was less enthusiastic).
Dodd espoused the merit of WSPR for antenna comparison in his article (Dodd 2011).
He documented a series of WSPR spots of his transmitter on 20m in a table swapping between antennas during the test period, one side of the table for each antenna. (Don’t be misled, the dipole is not half wave dipole but some non-descript multi band loaded dipole.)
He calculates the average for each data set and states:
The average from the dipole and the loop -16.74 and -17.0dB respectively meaning that the performances were very similar.