QRP Labs multi band receiver builders notes #bpf #polyphase #rcvr #vfo #gps

Mike Berg

The heart of this project is the VFO kit which controls an included Si5351A DDS.
It uses the same pcb as the U3S kit with several parts omitted making for easy construction.
VFO output is CLK0 on the DDS pcb and I used a short length of RG-174 soldered to signal & ground.
The coax connects to the bottom of the receiver pcb where it says  "LO".
I recommend using the GPS. For $23 you get a very accurate radio in return.
The 4 GPS lines from the VFO are connected to the DB-9 jack on the back of the enclosure. 
The GPS sits atop the case blinking away.
Power in +5v is from a 1A 7805 regulator.  In this build I had the regulator grafted to unused space on the VFO.
After building my U3S, I prefer it dead bugged on the coaxial power jack along with bypass caps.
Next is the 5 band relay kit which will plug into the VFO pcb via an included long, 5x2 10 pin header.
The relays are powered and switched via this connector.
The builder may opt to cut the RF in and out pins to prevent the received signal from going to the VFO pcb. I did it to mine.
The relay pcb has a number of jumper connections and the bandpass version is wired differently.
See the QRP Labs relay kit webpage for the docs. 
The RF in and out coax cables will be connected to the respective pins at the 5x2 header location on top of the relay pcb.  
RF in comes from the BNC connector. RF out goes to the receiver RF in at the bottom edge of it's pcb.
The receiver kit includes one bandpass filter, you'll have to buy the other four and construct them all.
I tuned mine using a HF rig with the filter in series with an antenna, going for strongest noise/signals.
I also placed extra nylon spacers between the relay/filter pcb and receiver to allow for access to the filter bank.
The receiver is built without the RF input switches and band pass sockets. I bypass these by connecting to RF in at the pcb bottom.
I also omitted C1, C2, TR2 and the audio jack. Audio out is taken from the receive pcb bottom "I" connection.
+5v power is supplied directly from the regulator output and also connects at the receiver pcb bottom.
The Polyphase pcb is built as per instructs. I used a 2x3 pin header with two jumper shunts for USB/LSB select.
The polyphase power and signals are routed via 3 - 3 pin/socket connectors to the receiver pcb.
Audio level out is adjusted with a variable resistor on the polyphase pcb.

So far, this rig is a dream to operate on WSPR covering 160m, 80m, 40m, 30m and 20m.

Mike  N0QBH

Fred Piering

That is really cool, Mike. Well Done!
Fred. WD9HNU


Hi Mike,
congrats in figuring out all the mutilband connections. I also built a similar rx but I found the vfo option gave me a lot of birdies and clicks as I tuned across the bands. I eventually rebuilt it as a U3S so it would band hop on fixed frequencies with wsjt-x sequencing which was better for wspr operation. 
I wonder if you have measured the actual sensitivity of your rx? I would be interested to know as my setup turned out to be a bit deaf(10uV for faint discernible trace on wsjt-x waterfall).

73 Ken G4apb 

Mike Berg

Mine is for mostly WSPR and other digital modes so I use the presets to accommodate.
Can't speak to the multiband sensitivity yet, but I empirically compared my earlier QRP Labs receiver on 30m to my FT-1200 and was encouraged enough to build this.
Next I plan to put together a sweeper to optimise the band pass filters as they are easily removed.  It'll be interesting to see what they "look" like and how well my "by ear" method worked.
I do enjoy building and using this gear - perhaps that is what it's really all about.

73 Mike  N0QBH