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
Steve (G3TXQ) posted a graph comparing Cecil’s (W5DXP) measurements of two turns on FT240-52 and FT240-K.
It is interesting to reconcile the #52 curves with Fairrite’s datasheets. A simple reconciliation is to compare results at the frequency where µ’ and µ” curves cross over. Continue reading Attempting to reconcile W5DXP & G3TXQ’s comparison of K and 52 mix ferrites
Among forum experts, there are ready recommendations for the ideal ferrite material (or mix) for a balun, often without knowing any detail of the application.
The ‘magic’ mixes include K. Perhaps they are devotees of Sevick.
Over some years I have searched for manufacturer’s data on K mix, and found only two references:
- Amidon who give a very brief table summarising characteristics, inadequate for RF inductor design; and
- Ferronics who give characteristic curves, albeit in less common format.
Problem is that Ferronics µi is 125 against Amidon’s 290… so their K materials are different.
One has hoped that an interested competent person might have made measurements of some samples from Amidon to give full characteristic curves, it isn’t that hard. Continue reading Ferrite K mix
I have been doing some research on APRS recently and acquired a used Paccomm Tiny-2 MK-II TNC, a TNC-2 clone.
Above, a top view of the PCB. Continue reading Paccomm Tiny-2 MK-II TNC review
The subject question is often asked, and the usual responses are mindless recitals of Rules of Thumb (RoT).
In the light of the discussion at Feed line length affect on VSWR and The half waves of coax rule for measuring VSWR accurately, lets consider the subject question and develop a rational answer. Continue reading Where is the best place to measure feed point VSWR
Lots of hams recite a rule that accurate measurement of VSWR can only be made at the feed point or an integral number of electrical half waves from the feed point.
It is one of those ‘rules’ that the proponents cannot usually explain… they would regard themselves as experts, but blindly follow folk-lore that they do not understand. Continue reading The half waves of coax rule for measuring VSWR accurately
In earlier articles I documented a trial of aprx v2.08r593:
Encouraged by Kenneth Finnegan who merged some fixes by WB4XO (which still didn’t work properly), I set about resolving some problems.
Further fixes and some enhancements have been pushed to the source fork at PhirePhly/aprx which in time may pull the changes.
. This was forked from
You can browse
for brief descriptions of the changes.
Recent Debian packages for RPi based on my fork have been uploaded to http://owenduffy.net/files/aprx/ .
A reader of my article End fed wires – new hams love ‘em asked about the performance of the matching transformer described at (Osborne 2014).
(Osborne 2014) gives the transformer design above using a FT82-43 ferrite toroid with three turns on the primary. The concept is to adjust the antenna length and C1 for a ‘perfect match’. Continue reading End fed wires – another matching case study