external antennas feature of the RF2K-S power amplifier

The RF2K-S solid state amplifier has a number of outstanding features. One of them is the way of dealing with complex antenna configurations. As a standard user you choose „internal antennas“ in the antenna setup if you up to 4 antennas connected to your amp. The 4 antenna outputs at the back of the amp can be configured by band and the antenna tuner can be programmed to handle the 4 antennas. This might be a 4-band yagi, a tri-band vertical, a double dipol and another tri band yagi.

In case your antenna setup is more complex / you use more antennas there´s a very interesting feature implemented. It´s just called „external antennas“ in the antenna menue. Take a quick look at my antenna setup which might be typical for a medium size contest station:

DF9LJ contest station antenna setup


I build up a SO2R contest station and decided to go for two amplifiers. There are amps on the market that claim to have SO2R capabilities and I tried one but it turned out to be good marketing instead of offering a suitable feature for me.

Other amps might do better but as SO2R operations normaly means to operate on two bands and often you use a tuner for your solid state amp. Then there´s always the need to switch the tuner when transmitting on another band which takes some time and creates some noise. But thats not the main topic of this post.

What I basically did in my antenna setup is switching the contest bands with a six-pack or 2×6 switch (band pass filters are omitted in the above sketch) allocating the bands to one of the radios and use one stack-match per band for selecting up to three antennas per band or any combination of the three antennas.

If I use 3 yagis in different directions of 20m I can choose any of them or any combination like JA plus W.

Solid state amps a more sensitive than the good old tube amplifiers. The LDMOS power transistors are normally well protected against any potentially harmfull operating conditions. It make a lot of sense to use the build in tuner to ensure low reverse power for any of the choosen antennas.

And here comes the feature „external antennas“. If you activate this feature on your RF2K-S only antenna output no.1 at the rear panel will be active as all the antenna switching is done outside of the amp (external). The ACC connector at the rear of the amp starts sensing a 4 pin/bit BCD input for distinguishing your extenal antenna setup.

I build my own antenna controller that produces an BCD for any of the used combinations. An output of 0 is generated if only the antenna 1 is used at the stackmatches. The build in antenna tuner of the RF2K-S uses the stored settings for antenna No.1. As any tuner setting for an antenna is storing the band segments for all bands I have the tuner settings for (in my case) 6 antennas (160,80,40,20,15,10) addressed if theres a BCD 0 at the ACC input.

The same is true for BCD 1 an 2. The tuner knows that there are different antennas connected now. It can be a dipol on 160 and 80, another yagi on 40m or whatever. It´s just a diffent set of antennas on every band that can be addressed by using a different BCD input at the ACC connector.

The stackmatches also allow any combinations of the three antennas available per band.

They are just coded as different BCD outputs by the inteligent antenna switch. A BCD code of 4 tells the tuner that the values for a combination of Antenna 1 and Antenna 3 are used on the active band.

The above setup uses 3 different antennas on the six contest band plus any combination of those. That makes 7 virtual antennas times 6 bands = 42 combinations.

For this setup I´m just using 7 BCD combinations. The amp can read 16 combinations times the number of bands you are using and once the tuner is programmed you´ll always have a perfect match of your RF2K-S.

If you wanna be prepared for winter where ice on your antennas is some issue just use another tuner bank and use the tuner bank 2. With that you can double everything I described above.

What an amazing feature. I haven´t seen this on any other amp yet.



Eine Antwort zu „external antennas feature of the RF2K-S power amplifier“

  1. Klasse !! Bei SO2R ist es nicht nur der Tuner der geschalten werden muss, sondern bei QSY auch die LPF. Klackert also auch wenn man keinen Tuner verwendet.

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