What It Takes by Wes Cosand, WZ7I

The following article was contributed by Wes, WZ7I, one of the longest-running RBN node-ops at 10 years and counting.  As you know if you follow such things, Wes is one of the most prolific spotters as well.  The number of spots and the SNRs his station produces are proof of how well it works. Here's how he does it:

Pete, N4ZR, emailed recently asking if I would describe the antennas and equipment that generate the data sent to the RBN.  I feel awkward doing this because I’m a biochemist, not an engineer, and I certainly am not presenting this as an optimal receiving station.  Rather I’m describing the current state of the jumbled mess that evolved in my basement.  If you promise not to laugh, here is a snapshot.

When I started contributing to the RBN  ten years ago my priority was to make it possible for the “rag-chewing” ham to know when his friends were on the air and to allow the casual DXer to find CW contacts.  I used a HyGain “HyTower Jr” wire-loaded vertical, the Clifton Labs 11dB Norton preamp, and when it became available, the QS1R and Skimmer Server.  The HyGain vertical with 32 radials worked pretty well on the wet ground in the woods and I was proud of how the neatly the equipment was laid out on my bench above.

But as the number of RBN nodes in the northeast US began to grow it seemed like just another contributing omnidirectional receiving station didn’t add much value.   It also bugged me that Dave, K1TTT, could hear stuff on his vertical that I couldn’t.  I had discovered that reading brought me more joy than operating so my transmitting antennas were sitting idle.    Over a period of years I began to use the transmitting antennas for skimming. 

I didn’t have much luck using power combiners to feed the input of the QS1R with multiple antennas.  I know other operators more skilled than I  have had marked success using this technique. I attempted to balance the noise from my HF beam with my “shorty forty” using attenuators and preamps but I never got it to work.  So when the Red Pitaya became available with two inputs I saw that as a marked advantage.  I’ve still had to be cautious because in my hands the isolation between the inputs is not great.  Perhaps I should limit my comment to say I often destroyed the sensitivity of the RP when I attempted to combine antennas. 

Here is a diagram of the three antennas I’m currently using to generate the HF spots on the RBN:

The QS1R and the low band CW / RTTY Red Pitaya each have a PC dedicated to them running the following software

·         Skimmer Server

·         CWSL

·         RTTY Skimmer

·         CWSL_SSBWave (or HDSDR)

·         Virtual Audio Cable

·         RCKskimmer for PSK31/63

·         WSJT-X for FT4

·         Dimension 4 for timing

The FT8 Red Pitayas have Pavel Demin’s FT8 receiver / decoder and the “upload-to-RBN” software from  Björn, SM7IUN.  I find this solution robust and quite sensitive. 

In the earliest days of RTTY skimming I embarrassed myself with RTTY spots that were off-frequency so now the frequency of the  QS1R is disciplined by a GPS unit from Leo Bodnar.

The Sommer antenna is 30 years old and may have faulty components now.  Its performance has always been better on 20 meters than 17, 15, 12 and 10 because on 20 it has a five element closely-spaced log periodic covering the band.

Six meter skimming has been a source of frustration to me because I have no experience operating on the band.  After multiple failures I have a system that has been stable for a couple weeks … chuckle.  I have a stack of two PAR electronics OA-50 dipoles mounted on the side of the tower feeding a tower-mounted ARR P50VDG preamp through an Alpha-Delta surge protector.  About 170 feet of Davis Bury-Flex runs to the basement where it goes through an additional surge protector.  The 12 volts for the preamp runs up the tower in old RG-213 with the shield well grounded at the top.  Currently I’m using a dedicated Red Pitaya and a copy of Skimmer Server set to “Aggressive” filtering.  In addition this computer has the CWSL / HDSDR / WSJT-X stack for FT8, FT4, and MSK144.  I would welcome anyone’s suggestions about how I might improve the sensitivity and, especially, the robustness of the system.

After watching the sensitivity of FT8 I am intrigued. I would like to try operating the mode and if I ever get my HF transceiver back from the repair shop I’m planning to turn off the skimming system during the weekdays and get on the air, at least for a time.  But I plan to be back on the RBN during major contests.