RX Antenna Distribution System

11 Jan 2014 by sm0w, No Comments »

During last year I have been thinking alot about how to distribute RX antennas to different operating positions at the station. Like the rest of the antenna switching the scope is different, allowing contest operations in different configurations like SO2R, M/S, MM. Working regular DX and also good remote switching capability. All ideas and possibilities was cooked down to an RX Antenna Distribution System.

Main parameters that I had to do was:

1. System should be able to be controlled by the openASC system.
2. As little electronics as possible at the beverage switching hubs in the forrest 150m away from the house.
3. Three operating positions should be able to use any of 14 possible RX antennas, even simultaneously!
4. Few feed cables into the forrest
5. Few control cables to the forrest.
6. Low loss even when several RX'es use the same antenna.
7. Possibility to switch on preamp.
8. Good filtering not to blow RX'es if several transmitters are at use simultaneously.

The RX antennas (beverages) are fed into two hubs which are about 150m away from the shack/house in the forrest. From there I will run three 150m long 1/2" hardlines to the house. The two hubs 50m apart are also connected by three RG-58/RG-213 feedlines. There will be a 2x10pair control cable from the house down to the forrest as well.

RX_Antenna_SystemThis is a basic scetch of the whole system. Two relay switching cards (antenna hubs) in the forrest are connected to the 150m long feedlines going up to the house. In the house I will build an 1RU box containing the following cards:

1. RX Antenna Combiner Card
2. RX Antenna Patch Card
3. openASC Driver Card
4. Arduino Microcontroller
5. 3×3 Band Bandpassfilter Cards (160,80 & 40m)


Here is a layout of the current Beverage antenna park. 10pcs of ~500m long beverages.

The relay cards in the forrest (RX Antenna Selector Cards) are controlled by the 2×10 pair cable run down from the in-house unit. There are about 60 relays in the RX Antenna Selector Cards that needs to be individually controlled so I decided to multiplex the control signals from the house down to the forrest and de-multiplex the signals there so with just 4 bits per "RX-Line" (total of 3) = 12 bits = 12 control lines I can control all 60 relays. It will also be very easy to control antenna selecton this way through the openASC system since I can assign several driver outputs for each antenna in the system.  Each of the three "RX-lines" has the possibility to use any of 14 RX antennas.


RX Antenna Selector card. Schematic here. RX_Antenna_Selector

So when any of the 3 operating positions that will have RX antenna capability selects an antenna in the openASC system the RF signal from that antenna is routed up to the house and into the RX Antenna Combiner Card. This card assures at all times that in and out impedances are correct. If two RX'es use the same antenna one of the incoming feedlines from the forrest is disconnected at both ends by relays and if the RX'es are on different bands the signals just pass on to the Bandpassfilter cards. If the RX'es are on the same band there will be 0 degree hybrid combiners connected to always assure the right impedances are used before the signal is passed on to the Bandpassfilters. If the RX'es use the same antenna on different bands the Bandpassfilters work like passive splitters only introducing the low passband loss of about 0,5-2 dB (frequency depandant) between the antenna and each RX since the filters only filter out the incoming energy of the actual tuned frequency and blocks all other signals with the high impedance input outside the passband.


RX Antenna Combiner card. Schematic here. RX_Antenna_Combiner

The Box contains three independent Bandpassfilter Cards originally designed by OH2U for 160, 80 and 40m. Mike SJ2W made PCB designs for the filters that I will be using in the box.

bpfThe Bandpassfilter cards are used as passive splitters and also as "pure" bandpass filters to protect RX frontends when there are several transmitters at work simultaneously.

The selection of the correct filter is also done with the openASC system. openASC detects the band that the RX/TX is on and activates an output in the driver card. To minimize the amount of outputs used in the driver card I have also decided to multiplex the signal by 2-bit encoding. The multiplexing between the openASC driver card and BPF cards are done on the RX Antenna Patch Card that also distributes and filters signals to and from the driver card and forrest. Filtering includes lowpass filters on all control lines and varistors. The RX Antenna patch card also distributes the 4 bit antenna selection data and 2 bit band selection data to an Arduino microcontroller that I will program to control the Combiner card depending on all different scenarios of:

1. Different antennas/different bands
2. Different antennas/same bands
3. Same antennas/different bands
4. Same antennas/same bands


Picture of the RX Antenna Patch Card. Schematic here.RX_patch_card

This project will be continued! =)


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OJØR Market Reef

OJØR Market Reef

OJØR is my callsign during visits to the barren rock of Market Reef in the middle of the Baltic sea. [&hellip