|[AMRadio] Classic Link Coupled Tuner|
rbethman at comcast.net
Sat Aug 15 13:20:13 EDT 2009
Thank you John!
You said it in terms that I wasn't dealing with at the time. I was
still working on my first cup of coffee, and being pestered by a 13 1/2
year old ShiTzu, that wanted a snack and another run outside to take
care of business. <sigh>
Makes it hard to keep the thought train running in the right direction.
The effects of link coupling are significant. You've pointed it out
VERY well! I haven't used a swinging link since building a 4-1000 amp
with the info from Eimac.
Mostly I deal with rotating links.
Bob - N0DGN
John Coleman wrote:
> In a link coupled assembly the coupling actually has an effect on the Q, the effective load. But increasing the Q of a parallel tank (less coil more capacitance) will increase the coupling. Using taps on the coil for the antenna connections reduces the coupling while increasing the Q. The fewer turns there are between the antenna connections the greater the Q of the tank but less voltage is coupled to the antenna. The coupling between the link and the main tank increases because the Q of the main tank went up as it was loaded less. The voltage across the ends of the main tank will go up as the taps are moved towards the center. You can get a different run of coupling by tuning the link in parallel instead of series. But this will double the voltage across the link capacitor. You can get yet another run of different coupling factors by using a swinging link.
> It all boils down to this: The tuner should be adjusted so that there is no L or C reactance at the antenna terminals. Then the coupling is adjusted to pull the current from the rig so that Erf/Irf = desired Z-load (generally 50 ohms).
> If the Q of the circuit is not high enough you will not be able to couple enough energy out of the XMTR to draw enough RF current to get the desire E/I (LOAD resistance) low enough.
> If the Q is too high in the wrong place then the circulating currents in the tanks of the tuner will either have high loss or begin arcing. If it aint getin hot and it aint arcin then it's OK.
> There always a number of ways to do it.
> BTW: I was in your neck of the woods a couple of weeks ago visiting with Kids in Searcy and drove out to the Peti-Jean park. I guess we must have gone right by you place.
> John, WA5BXO
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