K3PA Reporting from Kansas

Here's another variation on the equipment used by some of the most prolific RBN nodes, from Drew, K3PA:

"As the tradeoff between low band overload and high band sensitivity is so often noted, here is the approach I took.  I wanted to spot 10 bands (incl 6M), and so needed two QS1R units in any case.  I use a 18 foot vertical with a unity gain buffer (a YCCC RX circle amp) for 160 through 15m on the -1 node.  It has reduced sensitivity on 15M and up, due to the antenna design AND the buffer, AND the QS1R.


So, to spot 15/12/10/6, I have a separate antenna, an omni horizontal, basically a clone of a multiband "spider", which we used to call a "squalo" on 6M.  That antenna has a low noise figure, high intercept 16 dB gain preamp on it.  (Homebrew MOSFET type)  It generally hears better than the vertical on those bands.  I let both skim 15M with separate IDs as either can be better on 15.


As a benefit, I believe I have the only 6M node in the central US area.  I'd like to get it a little higher and away from household spurs but it does OK.


Jeff, AC0C is in my immediate geographical area also, and he has a more complicated setup leveraging his main TX antennas as well as an 8 circle and a vertical.  He also skims RTTY.  But no 6 meters there.  His node hears extraordinarily well on 160.  (Ask the east coast guys.)  Similar to me on other CW bands."  

I hope you're finding this series interesting and perhaps even inspiring.  Europe's next. 

73, Pete N4ZR

W3LPL's Solution by Frank Donovan, W3LPL

Somewhat in the same vein as my last post, about WZ7I's RBN node, here is W3LPL's setup, in his own words (warning, this post may trigger severe aluminum-envy):

I use an extremely complex system of nearly two dozen large antennas

feeding a nine port combiner that then feeds a single QS1R.

The secret to the combiner design is my W3LPL band pass filters (Google it). 

Unlike many filters, my band pass filters have approximately 50 ohm

impedance in-band and are high impedance out of band. This characteristic

allows the output side of up to five filters to be connected together to

form a frequency selective signal combiner.

I built a low band combiner and a high band combiner that capitalizes

on this band pass filter characteristic:

     - a 160, 80, 40 and 30 meter combiner, and

     - a 20, 17, 15, 12, and 10 meter combiner.  

The two combiners feed a 3 dB splitter -- operating as a passive combiner --

which then feeds the QS1R input.

A Clifton Labs preamp in front of each of the 17, 15, 12 and 10 meter filters

optimizes QS1R sensitivity on those bands.  Additional bandpass filters at the

inputs of each of the 17, 15, 12 and 10 meter preamps protects them from overload.

This arrangement results in an excellent nine input signal combiner with

one output feeding a single QS1R.

Treating each band independently (they are highly isolated from each

other), these antennas feed each of the nine combiner inputs:

160 meters:  any combination of receiving antennas manually selected

by a K9AY switch feeds the combiner.  The most frequently used receiving

antenna is a 160 meter  W8JI/W5ZN/N4HY eight circle array pointed NE.

80 meters:  any combination of receiving antennas manually selected

by a K9AY switch feeds the combiner.  The most frequently used receiving

antenna is an 80 meter W8JI/W5ZN/N4HY eight circle array pointed NE.

40 meters: two 3 element full size Yagis feed the combiner through a

matching transformer.  The most common configuration is a 3 element

Yagi 200 feet high pointed NE and a 3 element Yagi 100 feet high pointed

at 130 degrees azimuth.  When the 40 meter transmitter is transmitting

during contests, a relay switches the combiner input to any combination

of receiving antennas manually selected by a K9AY switch.  The most

frequently used receiving antenna is a 40 meter W8JI/W5ZN/N4HY

eight circle array pointed NE.

30 meters: a full size 3 element Yagi 120 feet high feeds the combiner,

typically pointed NE.

20 meters: three six element Yagis feed the combiner through a matching

transformer.  The most common configuration is a 200 foot high Yagi

pointed at 120 degrees and a pair of stacked Yagis pointed NE.  When

the 20 meter transmitter is transmitting during contests, a relay switches

the combiner input to a four square receiving antenna typically pointed NE.

17 meters: a 5 element Yagi 120 feet high feeds the combiner, typically

pointed NE.

15 meters: three seven element Yagis feed the combiner through a matching

transformer.   The most common configuration is a 200 foot high Yagi pointed

at 120 degrees and a pair of stacked Yagis pointed NE.  When the 15 meter

transmitter is transmitting during contests, a relay switches the combiner input

to a four square receiving antenna typically pointed NE.

12 meters: a 5 element Yagi 130 feet high feeds the combiner, typically

pointed NE.

10 meters: three eight element Yagis feed the combiner through a matching

transformer  The most common configuration is a 200 foot high Yagi pointed

east and a pair of stacked Yagis pointed south.  When the 10 meter transmitter

is transmitting during contests, a relay switches the combiner input to a

four square receiving antenna typically pointed south.

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.