Gerald, To a large extent the desirable high resistive component is inherent in the choice of core material, but the stray capacitance can also give useful benefit. Here's an example: A single turn o
You can then try inserting a choke at the feedpoint in the EZNEC model and see how it does indeed change the SWR on the feedline! The SWR is bound to change under those conditions. If you have a low
The #2631803802 part (FT240-31 for shorthand) is classified by Fair-Rite as a "Round Cable EMI Suppression Core", for which they have a single generic drawing which is "long and thin" whatever the ph
Jim, Any views on why they did that with Fair-Rite ferrite parts, but retained Micrometal's part numbering for Iron Powder toroids? Steve G3TXQ Actually, FT240 and similar part numbers were cooked up
This revision of TLW corrected some overly optimistic loss figures in its database for window line - it originally showed half the loss that you would expect from just the copper loss. An excellent a
If the voltage for a given power under matched conditions is V, the maximum voltage with an SWR of 2:1 will be 1.414*V, not 2*V. Same for current: 1.414*I Steve G3TXQ ________________________________
Ever since I got my OmniVI I've been annoyed by a low level heterodyne whose pitch is independent of the main tuning but which changes rapidly with the PBT setting. There was some discussion of it on
Apologies - wrong list!!! Steve G3TXQ On 02/08/2014 12:31, Steve Hunt wrote: Ever since I got my OmniVI I've been annoyed by a low level heterodyne whose pitch is independent of the main tuning but w
Rick, I already corrected this misunderstanding once: for a 2:1 SWR the maximum voltage will be 1.414 times the matched voltage, not double! The minimum voltage will be 0.707 times the matched voltag
You're correct that any power dissipation due to the voltage will be twice the matched case dissipation. But I thought - perhaps mistakenly - we were still discussing voltage breakdown? Steve G3TXQ Y
Yes, the voltage maxima are coincident with the current minima, so maximum dielectric loss will be coincident with minimum copper loss. How much those two offset each will obviously depend on their r
Agreed! However another factor in the design process is the duty-cycle of the mode. Voltage breakdown is likely to be pretty much instantaneous and mode independent; but excessive thermal dissipation
On a mismatched line - whatever the load impedance - the voltage and current maxima are a quarter-wave apart. Steve G3TXQ If the load impedance is resistive, whether 50 ohms or not, the voltage and c
Unlike some more conventional Yagis the feedpoint impedance at the centre of the Moxon Driven element is very close to 50 Ohms; you just need a Common-Mode choke at the feedpoint to reduce the likeli
It's worth noting that the two 1:1 current baluns forming a 4:1 Guanella balun will likely have very different CM voltages across them, leading to very different core dissipations. In fact if the two
I'd be very interested to hear how you managed to achieve that, and how you measured it. I've never measured any air-cored coax choke that achieved 500 Ohms (or more) over a 33:1 frequency range; les
Jim, Yes - I've measured the inductance using a low frequency meter "just for fun"; but that's what it was - "just for fun" - it tells you little about the high frequency CM impedance of a choke, for
With 7 turns of RG58 on four stacked FT240-31 cores I measure 298uH. That's broadly consistent with Fair-Rite's published figure for the Initial Permeability (1500). Steve G3TXQ CM Z of a choke. I wa
I have a spreadsheet which does pretty much what Jim just described. One thing that interested me when I started looking at the "best fit" equivalent-circuit values was that the value of C varied dep
Jim, If I wind exactly the same number of turns of the same cable with identical spacing on the same-size toroids, but use two different core materials, I get very different values of equivalent C. T