Varactor tuned FM yagi

FM antenna discussion
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Bert Jan
Posts: 3
Joined: 25 Sep 2016 23:23
Location: Apeldoorn NL

Varactor tuned FM yagi

Post by Bert Jan » 10 Jul 2019 00:36

Because I like experimenting with antennas, I built a varactor tuned FM yagi with 3 elements.
Every element has a BB640 in the middle. The open dipole one on each side.
With a box with 3 knobs I can adjust the DC voltages, which means electrically reduce the lengths.

With this 'gadget' I can tune for maximum gain (about 7 dBd) ór cancel out unwanted signals. With some stations I can reach
an attenuation of 45 dB but this isn't the case for every station.
The capacity (3 till 70 pf) is just enough to cover the FM band.

The elements have lengths that normally wood tune on about 85 Mhz. (the dipole even is 1.80 m wide)
I draw it in MMANA it appeared to be possible. I already had good results with Es and tropo.
In 2016 I started with a folded dipole but now I changed it to open one and this is a real improvement.

Has anyone experience with this concept ? ... -with.html
reception of Santis- CH 107,8 Mhz

73, Bert-Jan, pa1bj, Apeldoorn nl

Tim Bucknall
Posts: 3141
Joined: 01 Oct 2014 14:55
Location: Now stranded in Congleton

Re: Varactor tuned FM yagi

Post by Tim Bucknall » 06 Sep 2019 10:14

Great work!
Rx: Burkhardt Reuter RDR54D1, Elad FDM-S2, Airspy HF+ w/ HS Publications 6 Element R3 -R5 Yagi on rooftop rotator V/H polarization options. Pira P275 RDS analyser

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