Ham lore has it that man made noise on lower HF is radiated predominantly vertically polarised, this is offered and accepted by hams without explanation.
It can be shown by simple observation that the ambient noise level on lower HF is quite different in business or commercial areas, residential areas, and rural areas (ITU-R P.372-12). Not only is there a significant difference, the change happens quite rapidly with distance which suggests there is a dominant component (man made noise) and that the propagation path is a very local one (ground wave).
If you look around a typical residential neighborhood where hams might establish stations, the most obvious conductors that might carry and radiate noise currents from noise generators like appliances, leaky insulators etc are aerial power lines… which are usually closer to horizontal orientation (with horizontal E field) than vertical which seems inconsistent with the common observation that vertically polarised receiving antennas tend to capture more man made noise power than horizontal ones.
This article proposes a mechanism that may explain the apparent inconsistency between noise radiators and noise receivers.
Though this explanation is based on experience, the quantitative analysis here depends on interpretation of Recommendation ITU-R P.368-9 (2/2007) Ground-wave propagation curves for frequencies between 10 kHz and 30 MHz.
Whilst P.368-9 publishes a set of graphs like the one above for a limited set of grounds, ITU-R also publishes the program (GRWAVE.EXE) which can be used to calculate values for the user’s choice of ground and that is what was used for this article. The graph above is for a vertical monopole over ground with 1000W radiated, the antenna has directivity of 3, and the dashed line (inverse distance curve) is the field strength for a lossless ground (PEC). This can be verified with a spot calculation at 1km. Continue reading Polarisation of man made noise
Effective Isotropically Radiated Power (EIRP) is one means of comparing the performance of a transmitting station.
An inefficient antenna can lead to very low EIRP, perhaps surprisingly low. Consider these four examples at 3.6MHz,
The following NEC-4.2 models give some insight.
QW vertical with 120 buried radials
Considered by so many experts to be the benchmark for a grounded monopole, here is a quarter wave vertical with 120 buried radials.
Above, 120 buried radials: GAIN=-1.8dBi, radiation efficiency=20.7%.
At 1kW RF input, EIRP=661W. Continue reading Turning 1kW into QRP
I wrote at OCF short vertical dipole for HF that some authors and some sellers wrote descriptions that might entice would be implementors.
George, VY1GP, made a really nice video production of his pitch.
His Youtube video seems to have been substituted with one by Portune, so I have removed the link.
…but do the claims stack up? Continue reading OCF short vertical dipole for HF – VY1GP
The term Effective Radiated Power or ERP appears frequently in ham discussions, antenna literature and regulatory documents. Continue reading Effective Radiated Power (ERP)
The OCF short vertical dipole for HF has become popular, particularly disguised as a flag pole for low impact installations and encouraged by claims of outstanding performance. The antenna was described in QST and a commercial version was available at time of writing.
The rationale for the design is that it is a short dipole, not requiring radials, and feed point offset downwards by 30% as an optimal value for performance (driven by often unsound assessments of coax loss).
Off-Center Fed Vertical Dipole design means no radials, 90% efficient or better across 80m – 10m
Above is the promising gain plot for one of the commercial implementations, it is only one S point (6dB) behind a quarter wave vertical with 4 buried radials. Continue reading OCF short vertical dipole for HF
The CADWELDPLUSCU is the igniter for the Cadweld Plus line of electrically initiated thermite weld capsules. The plug seen on the end of the cable slides over the flat connection strip to the capsule.
The environment around the weld crucible is subject to a sudden ejection of hot gases and smoke, much of which is emitted out of the slot in a Oneshot crucible intended for the connection strip, and this is only a 45g capsule. There is probably less gas emitted towards the connector on reusable moulds as the gap for the connection strip is very narrow.
Despite dressing the plug away from the stream of hot gasses emitted, it can be seen above that the plug has suffered heat damage. Of particular concern is deformation of the parts at the cable clamp rendering it less effective. The plugs come on a new lead set that is relatively expensive.
Since one wants to be able to yank the cord away from the crucible as soon as possible to minimise heat damage, the cord grip needs to be effective.
This article describes two measures taken to protect the plug and ensure the cord grip works. Continue reading Cadweld Plus Control Unit
The MFJ-993B auto antenna tuner includes an internal balun, this article is a review of that balun.
The schematic shows the balun as a Guanella 4:1 balun with the usual external link to one of the coaxial antenna sockets. (The label “Z balanced” is misleading, clearly one of the terminals is grounded and this is the unbalanced connection to the coax connector via a link. The antenna connects to the left hand terminals.)
Unlike almost all ATUs with an internal balun, this is a current balun (to their credit), but a 4:1 balun.
There are two aspects of balun behaviour that are of particular interest:
- choking or common mode impedance; and
- impedance transformation.
Continue reading MFJ-993B internal balun review
At MFJ-993B on my G5RV with tuned feeder I discussed first impressions of the replacement ATU.
This article documents the physical layout.
The antenna is a G5RV with tuned feeders (Varney 1958). The tuned feeder is home made two wire line using 2mm diameter copper spaced 50mm.
Above at the right, the open wire line terminates on a home made balun on the feed line entrance panel, see
Design / build project: Guanella 1:1 ‘tuner balun for HF’ – #4 for details of the balun. This is all under the building eaves, but it is waterproof… the area is regularly jetted with high pressure water to clean insects away. Continue reading Shack entry / ATU configuration for my G5RV with tuned feeder
Upon reading Rationale for sizing of lightning down conductor a correspondent asks whether his premises 4mm^2 main earthing conductor ok as a lightning down conductor.
Intended purpose of electrical installation ground electrode
The usual source of current on the premises main earth conductor would be a fault energised by the incoming supply. To understand the implications, lets review the supply system. Continue reading Is the premises main earthing conductor ok as a lightning down conductor
The lightning ground conductor shown at Mast ground rework might at first seem excessive, this article sets out the rationale.
The connection to a 2.4m copper clad steel driven electrode (under the green cover) is 35mm^2 copper.
The nature of lightning protection sizing
Lightning protection sizing is a risk management regime driven by the mechanisms of lightning and variation in distribution.
It is not surprising then that regulatory standards in different distributions broadly use similar design methods but set different practices for implementation in the jurisdiction.
So, let’s go standards shopping… what we are looking for is guidance on the energy (or work) that is directed to heating the down conductor, and choosing a conductor size that will sustain not just a single stroke, or an average stroke, but most events that may include many strokes in a short period of time. Continue reading Rationale for sizing of lightning down conductor