David, VK3IL, describes a small transmitting loop (STL) at Portable magnetic loop antenna.
As far as I can glean from the article, it is made from a 3m length of LDF4-50B Heliax, and uses a Patterson match to tune it.
David offered measurement of VSWR around centre frequency for the loop matched on 40m. He has measured the VSWR=2.6 (the half power) bandwidth shown between markers 2 and 3 to be 22kHz. Continue reading VK3IL’s 3m circumference LDF4-50B loop on 40m
Peter, VK3YE, describes a small transmitting loop (STL) in his video at https://www.youtube.com/watch?v=Cv_RnLpZ9gw.
As far as I can glean from the video, it is made from a 3m length of copper tube 19mm diameter, and uses about 1.8m of RG213 to tune it, and appears to have its centre 0.7m above ‘ground’ .
Let us firstly look at a free space model of the antenna using Reg Edwards’ RJELoop1 tool.
This model has its limitations, but the calculated inductance is of interest. We can calculate the inductive reactance to be 118Ω. The capacitive stub of RG213 will need around 107Ω reactance, and solving for RG213, we find that 1.94m gives 0.19-j107Ω. The resistive component is important as it is ignored by the above model. The stub resistance is a loss resistance, and we need to recalculate the efficiency. Efficiency=Rrad/Rloss=0.005/(0.19+0.0351+0.005)=2.17% (-16.6dB). We can also calculate the Q as 107/(0.19+0.0351+0.005)=465 and half power bandwidth as 7100/497=15.3kHz. Continue reading VK3YE’s 3m circumference copper tube loop with RG213 stub tuning
Further to AIM 885 produces internally inconsistent results…
A new release, AIM885A appeared recently.
In the common theme of one step forward, two steps backwards, this version produces error popups when started.
The above popup appears twice when starting AIM885A. Just another symptom to undermine confidence in the system. It doesn’t make sense to me, and the program appears to otherwise start and run. Continue reading AIM 885A produces internally inconsistent results
Feeding at a current maximum visited the common practice of designing to feed a multi band dipole with open wire feed at or very near to a current maximum.
I explained that feeding at the current maximum may provide sub-optimal performance on the popular T-match ATU as its losses tend to be worst with low R loads, aggravated by the use of 4:1 baluns for even lower R.
On the other hand, feeding at a voltage maximum might exceed the ATU’s voltage capacity, or perhaps be outside of the matching range of the ATU.
Well if neither of these is optimal in all cases, what about half way between. It has been done, the odd eighths wave feed line on an 80m half wave is another of the recipes you will hear.
Lets explore the options of a half wave dipole at 3.6MHz with four different feed line lengths (Wireman 551). Continue reading Feeding at a current maximum, and three other options
I mentioned in my (revised) article W5DXP’s current maximum calculator that
lots of ham subscribe to the strategy of feeding a dipole / open wire feeder combination at current maximum.
Why is that? Continue reading Feeding at a current maximum
(Trask 2005b) describes a circuit at Figure 7 which the author describes as a 1:1 current balun though he does not actually define or reference a definition of the term
current balun. Continue reading Review of Trask’s 1:1 current balun
At Where is the best place to measure feed point VSWR I discussed location of the VSWR meter and projection of its reading to another point on a known transmission line.
A correspondent has taken me to task and citing Telepost’s LP-100A manual: Continue reading LP-100A manual advice on VSWR measurement
(Sevick 2001) discusses efficiency of transmission line transformers that use nickel-zinc ferrites in Chapter 11 “Materials and power ratings” applied to broad band baluns.
In Chapter 11 he reports a range of measurements of two different basic configurations, a 4:1 Ruthroff balun and a 4:1 autotransformer and uses nickel zinc ferrite cores of types that are no longer readily available (and none were the K and 52 mixes he is said to have recommended).
The types of transformers he built are ones where core flux (and so core loss) at low frequencies is approximately proportional to the quotient of voltage impressed across the input terminals and number of turns, so core losses can be decreased by reducing voltage and/or increasing turns. These are Voltage Baluns, see Definition: Current Balun, Voltage Balun.
By contrast, the flux (and so the core losses) in Current Baluns is proportional to the common mode current times turns, and in antenna systems, that cannot be simply calculated using back of the envelope ohms law (though pundits often do it), see Baluns – Rule 500.
So Seviks experiments and discussion are not directly applicable to Current Baluns, yet they are cited by manufacturers, sellers, and users as rationale for their designs using nickel-zinc ferrites for Current Baluns. Continue reading Sevick’s comments on selection of ferrite mix