RE: LF: remote antenna tuning

[Rik Strobbe <Rik.Strobbe@fys.kuleuven.be>]

Hi Stefan,

 

remote tuning of the loading should be done by optimizing SWR (at the TX), not for maximum RF current.

If one keeps that in mind there is no problem.

I am not sure if I will keep the remote variometer tuning. It needs some extra wires to the loading coil and I am not sure how long the small DC motor will function properly with all the rain and frost coming up.

Maybe I will change to a "classic" ATU (PI-filter version). Has anyone experience with that?

Some fast math tells me that the 2 caps need to be 0-4nF and the coil 0-15uH.

 

73, Rik  ON7YD

 

---

Van: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] namens Stefan Schäfer [Stefan.Schaefer@iup.uni-heidelberg.de]
Verzonden: vrijdag 8 november 2013 14:58
Aan: rsgb_lf_group@blacksheep.org
Onderwerp: Re: LF: remote antenna tuning

Hi Rik,

Thanks for sharing your experiences.
I also didnt expect that this effect is so noticable.
What do you plan to do now?
I am using a current transformer at the cold end of the loading coil and have a small analog meter to show the current (peak). And my antenna even needs a re-tuning when QSYing from CW to WSPR...
How do you match the coil to the cable? Directly, a tap or a ferrite transformer?

Am 08.11.2013 14:03, schrieb Rik Strobbe:

 By the way: remote tuning can be done correctly by tuning for best SWR instead of highest RF current at the TX output.

 

73, Rik  ON7YD - OR7T

I think the best is to accurately match the feedpoint impedance (at resonance Z=R+j0) of the antenna to 50 Ohm, by using a ferrite transformer. Then the variometer position of best SWR is the best working point for the PA (and the LPF). Highest RF current at TX output can quickly destroy the PA, especially class-E types :-)

73, Stefan/DK7FC