This is older THT version. New (SMD) version is there since 3/2022.

K9AY++ RX antenna system with BPFs, Preamp, Controller and much more

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The K9AY is terminated loop RX antenna. It consists of a wire loop of any convenient shape (diamond, delta, etc), hung from a single support and with a ground rod at the bottom. A 9:1 impedance-matching transformer is connected from one end of the loop to the ground and a terminating resistor is connected the other end of the loop to the ground. Antenna has got Band Pass Filters and Preamplifier in the feed point of the loops. It is advantage of filtering and amplification small signals directly from antenna. This antenna is directional. Favoring signals are arriving from the feed point end. You can also change the antenna far field by changing RLOAD (RTERM) of the loop. This set including the RF feeder box and the controller.

Main functions:

RF feeder box:

Antenna feeder block diagram:

K9AY matching unit


Controller block diagram:

K9AY comparation

K9AY controller block diagram


K9AY++ system includes:

Optional Common-mode current choke for coax and control cable


Band Pass Filters characteristic:

160m BPF

80m BPF

40m BPF

Band Pass Filters characteristic with preamplifier:

160m BPF with preamp

80m BPF with preamp

40m BPF with preamp

BYPASS with preamp


User review

  • Thanks for email from Robert HA2NP: Congratulations on your great work! First I built the small version of the antenna (3m high). The result is fantastic!The first QSO ZS6 on 80m, on one week around 100 DX on 80m. On 40m new african countries. On 160m I don't have a tx antenna, just a endfed antenna widh tuner, but there are 40 countries in a week ...Sometimes on 20m is also useful for antenna reception (spiderbeam for tx) when bandnoise is high... The controller box design is very nice, I am satisfied! Thanks.

  • Thanks for email from Vesa: Hi! I've been using K9AY++ several weeks now in mediumwave (broadcasting) dxing and my impressions have been only positive. It is always amazing to change the audible stations on the channel by adjusting the direction and resistor knobs. Lots of mediumwave stations from the Far East received so far and this evening at 1700 UTC I received even Australian ABC Adelaide 891 kHz under pressure of Asian stations on the channel. I could never have expected to receive Australian MW-station with K9AY! K9AY++ really rocks!

  • Thanks for photos from Laci HA7JTR:

  • by Laci HA7JTR-HA7I

    by Laci HA7JTR-HA7I

    by Laci HA7JTR-HA7I


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