A method for initial ground loss estimates for an STL

Over recent weeks, I have run literally hundreds of thousands of NEC models of small transmitting loops (STL) over real ground. The objective was to try to discover some simple methods for initial design of a STL, particularly an estimate of ground loss of STL mounted near natural ground. Continue reading A method for initial ground loss estimates for an STL

Mini60 antenna analyser

There seems a never ending stream of low end antenna analysers appearing.

The Mini60 antenna analyser is one in that vein, and is sure to prove popular because of its low price. As is common, there does not appear to be an English language user manual and the specifications in eBay ads are not very reliable (eg weight: 200kg).

Clip 010

Above is a screenshot from an online demo of the Mini60 on a 7MHz antenna. Continue reading Mini60 antenna analyser

Silicon Chip Collinear

This article has been copied by request from my VK1OD.net web site which is no longer online. The article may contain links to articles on that site and which are no longer available.

(Tester 2013) described a coaxial collinear array for VHF/UHF. Tester describes the antenna a collinear is a vertical antenna whose resonant elements are connected along a common line (ie co-linear) so that each element is opposite in phase to its neighbour.

He is a little confused, in fact, the elements are in-phase with each other so that in the horizontal direction, the contribution of the current in each element to the far field is an additive or reinforcing one.

He goes on to say [i]f you are not into antennas, that mouthful is, fortunately, very easy to achieve… but is it?

Implementation

 

CoCo1
Fig 1

Fig 1 is from (Tester 2013) showing the construction. Continue reading Silicon Chip Collinear

An A/B comparison of a low G5RV with a MobileOne M40-1 – statistical analysis

This article reports statistical analysis of the measurements made for An A/B comparison of a low G5RV with a MobileOne M40-1 (read it first).

I left it for readers to visually form a view of the difference between the antennas, and the implications for credibility of folk lore about the two antenna types, this article addresses the quantitative difference between the average S/N ratio of the antennas.

Statistical analysis

Standard statistical techniques can be used to arrive at a difference in the mean S/N of the antennas and to quantify the uncertainty in that statistic. Continue reading An A/B comparison of a low G5RV with a MobileOne M40-1 – statistical analysis

NEC-4 vs NEC-2 on a low small transmitting loop

This article compares a series of models of a small transmitting loop at varying height above real ground using NEC-4 and NEC-2.

The models are of an octagonal loop of thin wire of the same area as a 1m diameter circle over real ground (0.007/17). Height is measured to the centre of the loop, and all impedances are wrt the main loop.

Clip 176

Above is the NEC-2 result.

Continue reading NEC-4 vs NEC-2 on a low small transmitting loop

An A/B comparison of a low G5RV with a MobileOne M40-1

This article reports measurements on 40m of S/N as a receiving station in Melbourne of a 10W transmitter switched between a G5RV and M40-1 over a 1 hour period.

The experiment compares the antenna over a specific, but very relevant ionspheric path so it is more useful than ground level measurements in a car park or playing field.

SL1508152249

Above is a screenshot of the beacon signal switched between the two antennas. Continue reading An A/B comparison of a low G5RV with a MobileOne M40-1

Accuracy of estimation of radiation resistance of small transmitting loops

A simple formula exists for calculation of radiation resistance of a small transmitting loop in free space. The derivation is in most good antenna text books.

Screenshot - 14_08_2015 , 08_10_55

The expression depends on an assumption that current around the loop is uniform, so the question is what is the acceptable limit for loop size.

NEC might provide some guidance. A series of NEC-4 models of a octagonal loop of thin lossless wire in free space was constructed with varying perimeter. Perimeter shown is that of a circle of the same area.

Clip 004

Above is a comparison of the two methods of estimation of Rr. To the extent that we trust NEC-4, the graph indicates that error in the simple formula grows quickly for loop perimeter greater than 0.1λ. (The results using NEC-2 are visually identical.)

Many authors set the criteria for a small loop to perimeter<0.3λ, but it is clear that current is not sufficiently uniform for perimeter>0.1λ for estimation of Rr as 31149*(A/λ^2)^2 to 0.1pu error or better.

Small transmitting loop – ground loss relationship to radiation resistance

This article documents a series of NEC-2 models at 7.2MHz of a lossless small transmitting loop near ground for the insight that they might provide about underlying loss mechanisms.

Key model details:

  • lossless conductor 25mm diameter;
  • octagon of sides 403mm, has same enclosed area as a 1m diameter circle;
  • three ground types;
  • height varies from 1.5-10m to centre of loop.

Impedance elements discussed in this article are referred to the main loop. Continue reading Small transmitting loop – ground loss relationship to radiation resistance