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
Category: Transmission lines
Review of Trask’s 1:1 current balun
(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
LP-100A manual advice on VSWR measurement
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
Attempting to reconcile W5DXP & G3TXQ’s comparison of K and 52 mix ferrites #2
This is a follow up to Attempting to reconcile W5DXP & G3TXQ’s comparison of K and 52 mix ferrites.
Steve saw the above article and revisited the FT240-52 measurements which he apparently did, and found them wanting: Continue reading Attempting to reconcile W5DXP & G3TXQ’s comparison of K and 52 mix ferrites #2
Sevick’s comments on selection of ferrite mix
(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
Attempting to reconcile W5DXP & G3TXQ’s comparison of K and 52 mix ferrites
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
Ferrite K mix
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
The laws of physics – common mode currents and coax
I am always suspicious when “the laws of physics” are cited to support some argument. One forum expert recently offered:
The laws of physics require that the current on an ideal coax center conductor and the current on the inside of an ideal coax braid be equal in magnitude and opposite in phase, i.e. nothing but ideal differential currents can flow inside ideal coax. Anything else would violate Maxwell’s equations. All common-mode (non-differential) current must therefore necessarily flow on the outside of the ideal coax braid.
If we consider the end of a coaxial transmission line to have just two terminals, we can define some currents for the purpose of discussion. I1 flowing out of the inner conductor terminal, and I2 flowing into the other terminal (the end of the outer conductor). Continue reading The laws of physics – common mode currents and coax
Loss of Wireman 553 windowed ladder line at MF/HF – does it matter #2
Loss of Wireman 553 windowed ladder line at MF/HF discussed the matched line loss of a windowed ladder line with 19 strand CCS conductors.
Above, the loss curves from the article
You might look at this and ask “does it matter”.
A recent thread on QRZ (Any special consideration for long run of twin-lead?) gives an interesting example. Continue reading Loss of Wireman 553 windowed ladder line at MF/HF – does it matter #2
AIMuhf – my strategy
I have spent considerable time over the last few weeks trying to salvage something useful and reliable from the wreckage that is AIMuhf and its PC client program AIM. Continue reading AIMuhf – my strategy