Something old, something new: A four-band 5W/50W SSB/CW transceiver (‘Summit Prowler 7’)

‘Summit Prowler 7’ is my name for this scratch-built multiband SSB and CW transceiver. This rig covers four of the most popular portable, Parks and SOTA bands — 80, 40, 30 and 20m, at a power level of 5 watts, but with an in-built switchable 50 watt power amplifier, so that you have the option to call up the extra power if the going gets rough. The rig weights in at around 1 kilogram or 2.2 pounds, about the same as an FT-817, and is similarly sized. It’s a rig for a wide range of portable situations, and is equally at home on the shack bench.

Origin

A visit to the Eastern and Mountain District Radio Club Hamfest a few years back turned up a nugget — a hand made solid state SSB exciter, with crystal filter, bearing the call sign VK3WAC etched in the PCB copper. It was built in the tradition of 1980s discrete RF design with a 1496 balanced modulator and mixer, dual gate MOSFET IF stages, and a chunky crystal filter on 5.12 MHz by Netcom. The module was well made and complete, albeit somewhat tarnished, as if it had been stored in a damp shed or laundry. But the design and construction was evocative of the time and it was too well made and complete to ignore. I resolved to trace out the circuit diagram.

VK3WAC’s homebrew SSB exciter, found at the local radio club Hamfest.

The next find amplified its provenance. The copper side inscription read ‘VK3WAC NOV 1993 SSD P203/204’. I searched for VK3WAC without much success. I sent a message to whoever established the page on qrz.com. No reply.

The inscription. A bit of amateur radio anthropology required.

SSD P203/204. It sounded kind of familiar but it took a little bit of pondering until the penny dropped. Solid State Design for the Radio Amateur. Page 203. I hastily grabbed my yellowed old copy and turned up the page. Eureka! There it was, a complete description of ‘An SSB Exciter’, and it matched my board in every detail. This is a testament to board labeling. I am afraid anyone who picks up my homebrew projects in the future won’t be as well informed after I’ve moved on.

I powered it up. The crystal oscillator ran. So did the mic amp. Then the IF amps and filter. After replacing some eroded trimcaps and with an hour of basic alignment, I heard SSB at 5.12MHz. Now, what to do with it.

Netcom 5.12MHz filter

I wanted to determine the back-story and quality of the crystal filter. Some online research yielded little about 5.12MHz Netcom crystal filters, apart from a nearly identical one at Surplus Sales. That it appeared on a page of Collins filters gave me a moment of excitement. Maybe Collins used these filters at some stage.

The NETCOM 5.12MHz crystal filter.

I emailed Surplus Sales to ask about any specs and got a quick response from Bob, saying:

When we write the web page, all known data for filters in included. I know nothing else about this filter other than what is written on it. Interestingly, the filter in question does sell occasionally. I can make an assumption that like most Collins filters that are not used in the older vacuum tube equipment, the in and out Z should be low, normally around 50 ohms. No guarantee, just an educated guess.

So it is an ex- Collins piece. Crystal filters have long been prized possessions, having one would have been the motivation for making an exciter such as this. Based on how the SSB sounded in my initial test, the filter was not damaged, and had an SSB bandwidth.

The VK3WAC board could be made to transceive without much effort so I decided on an SSB/CW transceiver for HF bands, 80, 40, 30 and 20m. The VK3WAC board’s size dictated the overall physical size of the chassis. To increase its utility, a medium power PA that could be bypassed for QRP or smaller battery portable operation would be included. Not exactly a compact and lightweight Summit Prowler, but one for drive-up or slightly easier access summits.

Schematics

Page1 has the receiver and shared stages:

Page 2 has the exciter, driver, PA:

Page 3 has the microcontroller, si5351, buffering and control circuitry:

VFO/BFO/Controller/Keyer

The VFO, BFO, controller and CW keyer is an Arduino Nano, si5351, LCD and some supporting circuitry, built to the VU2ESE Raduino schematic. My script is here.

The boards in this module were sized to match the dimensions of the 16×2 LCD, and layered like a phenolic-and-copper club sandwich, in the interests of compactness. The disadvantage of this scheme is that each layer’s area is limited; consequently 3 boards were required, the first for the Nano, the second for the si5351, sidetone and T/R switch, and a third for the oscillator buffers. This isn’t such a bad thing — if not needed, the buffering board can be jettisoned just by pulling it off the assembly.

Receiver

A conventional single conversion superhet design was chosen to turn this exciter into a transceiver. A set of four 4-pole bandpass filters, built to the design of Eamon EI9GQ, then a dual gate, AGC controlled MOSFET RF amplifier using a BF961, switched with a pair of miniature relays to allow this first gain stage to be bypassed (think of it as a switchable RF preamp) complete the receiver RF stages.

The BPF and RF preamp is followed by a Minicircuits JMS-1 L7 diode ring mixer, driven by the buffered and padded si5351 clock 0. The VFO is high side, so with a 5.12MHz IF, runs at 8.62MHz on 80m and 19.12MHz on 20m.

Next, a class A post mixer amplifier, straight from the pages of EMRFD, using a substitute on-hand 2N2119A for the prescribed 2N5189. I’ve done this swap at HF before with satisfactory results. Then, the IF signal takes off to the first IF amp stage on the heritage exciter board (MFE131 dual gate MOSFET) with added diode T/R switching.

The post-filter IF return signal is brought back to the new receiver board to an SA612 Gilbert Cell product detector, then an audio preamp (BC549), and finally, the audio power amp (NEC ULN2002). AGC is derived using a two stage audio amp/detector, copied from Peter DK7IH’s circuits. All three MOSFET gain stages have AGC applied.

Transmitter

The balanced modulator and IF stages of the 1993 SSB exciter were used without modification. Using surface mount components a LM1496 transmit mixer and 2N2219A pre-driver were packed into the PCB bay originally reserved for just the 1496 14 pin DIL transmit mixer. These stages delivered a 5V pp signal on the transmit frequency at the output connector.

Two more boards completed the QRP stage of the transceiver — a board for an IRF510 QRP PA (or QRO driver) and another small board for the T/R relay and low pass filters, made to fit snugly into the bay originally housing the two 5.12MHz crystal oscillators (made obsolete by the si5351 clock 2). Miniature relays were used at the output of the IRF510 stage and the input of the low pass filter. These allow the QRO RF PA to be switched in between the IRF510 and LPF.

The QRP PA driver board with BD139 driver and IRF510 PA. The open space in the middle accommodates the back of the loudspeaker when the cabinet is assembled.
Under test. Signal source is a crystal oscillator and buffer on 3.579MHz delivering 1.5v pp. The QRP PA module delivers 4 watts into a dummy load.

Chassis, switchery, socketry

A custom chassis was assembled from 40mm aluminum angle, 2.5mm stock for the front panel, 1mm for the back and sides, on a 1.5mm bottom plate. Lengths of 10mm angle are riveted to the inner sides and rear to create a shelf for a 1.2 mm drop-in top panel. A 40mm angle divider runs down the centre line, dividing the chassis into two roughly equal bays, SSB exciter on the left, receiver, QRP and QRO PAs (and space for a loudspeaker mounted on the top panel) on the right.

Chassis made from hand worked 40mm aluminum angle. Sharpie marker pen for scale. Unused space on the rear panel is for the RF PA heatsink.

The panels were cleaned, black Deca-dry labels applied, then 3 light coats of clear satin spray. Front panel controls were minimised — liquid crystal display, tuning (optical encoder), audio volume, external speaker/phones, mic socket and a single push-button for changing bands. There is no tuning increment, it is fixed at 100Hz steps on all bands. Holding the push button down results in a 3 second tune carrier. A miniature toggle switches in the receiver preamp.

The minimal front panel pushed some controls to the rear panel, which had to be partitioned down the middle to allow for heat-sinking the QRO PA. The rear panel houses the PA heatsink, SO239 antenna socket, two push-buttons for keyer memories, a pair of banana sockets for DC power. I decided to omit the microphone gain potentiometer as previous experience leads me to think that this can be ‘set and forget’ on a rig of this kind.

QRO PA

Building a rig like this is done in stages. The transmitter core, the product detector, mic amp, IF strip were done by OM VK3WAC back in the heady days of 1993. That saved many hours of work. Adding a chassis, my Arduino/si5351 and receiver modules and a simple 5 watt PA got it to a working transceiver. After having played with it on the bench for a while, it was time to add a 50 watt PA.

I chose the W6JL amplifier, the QST homebrew competition winning design, which uses IRFZ24 FETs on a 13V rail. It’s simple and compact, and delivers a reliable 50 watts up to 20m. It is readily driven by a few watts, so an IRF510 with a bit of padding is a good choice of driver. There are many recent builds of this design, including by me and Glenn VK3PE. Don W6JL is a master homebrewer, if you haven’t seen his all-homebrew high performance station before check it out.

Custom board sized to exactly fit the available space on the rear panel. 

W6JL 50 watt amplifier module, mostly complete.
Showing the input and output transformers. The output transformer is on a BN-43-3312 core, 1 turn primary is RG58 braid, 3 turn secondary is Teflon inner from RG336 coax, which survives the heat from the soldering iron.
Fifty watt PA module complete.

Heatsinking is important for amplifiers with TO220 switching FETs. The IRFZ24s are not designed to switch RF and getting the heat away from the junctions is vital. I designed the board to allow the IRFZ24s to be bolted against the rear panel and heat-sink through a cutout in the board.

Specifications

Here is a brief summary of some basic specifications (as far as I can measure):

  • Transceiver coverage: 80, 40, 30 and 20m
  • Modes: SSB (automatic sideband selection), CW (inbuilt software keyer)
  • Current draw: Receive 220 mA; Tx low power 1.5A, Tx high power 7A
  • Transmit power: Low power setting: 3.5 MHz 8 watts CW, 7 MHz 10 watts CW, 10MHz 10 watts CW, 14 MHz 4 watts CW.
  • High power setting: 3.5MHz 40 watts CW, 7 MHz 60 watts CW, 10 MHz 60 watts CW, 14 MHz 30 watts CW.
  • Weight: 1,100 g, with microphone.
  • Size: 168 (W) x 250 (D case) x 40 (H) mm; depth including heatsink 280 mm.

On a Summit

My first outing with this transceiver was in the company of two other activators, Owen VK3EAR and David VK3KR. We started the day at Mt St Leonard VK3/VC-006, a 1,012 meter 6 pointer about 10 minutes drive north of Healesville, which is about 90 minutes drive north-east from home.

After St Leonard, we drove over the Black Spur to Mt Gordon VK3/VN-030, a 764 meter four-pointer south west of Marysville. Here, I set up the rig on 20m CW with the amplifier switched in and my linked dipole. A rapid string of chasers followed, VKs and ZLs, and the reports coming back were better than I’ve ever had on 20m. You can hear some of them in the video.

The final mountain for the day was Mt Strickland VK3/VN-030, a 1,068 meter six-pointer off the Acheron Way south of Marysville. Here, the late afternoon timing (around 16:30 local or 06:30 UTC) for HF CW was perfect and 40m was full of local and DX signals. I worked a string of chasers, the highlight being Jose EA7GV, who persistently called me until I noticed him between the VKs and ZLs, and he was able to report 339 from southern Spain. I gave him 559. He later told me via email how pleased he was to work his first activator on a VK summit. I reciprocated, my second ever European from a summit. A great way to end a day in the Yarra Ranges.

Further field testing followed at Mt Donna Buang VK3/VC-002 and Mt Vinegar VK3/VC-005. The video gives a good indication of the sound of the receiver on these quiet sub-alpine peaks.

Design notes

A few post-project thoughts.

Using a decent quality commercial crystal filter improves the receiver sound and performance significantly. I have homebrewed crystal lattice filters over many years, and I have to admit that the results have varied.

Some makers spend a lot of time on crystal selection, matching and tuning and they do get more consistently good results. While impedance matching around the filter input is non-negotiable (as is careful positioning and shielding), the whole game of adding a few pF here and there, swapping crystals, trying different batches, sweeping and re-sweeping — test, rinse, repeat — can get tiring. I have tended to carefully measure and match crystal frequencies but avoid obsessive optimising. As a result I sometimes have to live with the result.

Another common problem with homebrew filters is asymmetry — it can sound OK on LSB but a bit peaky on USB (or vice versa) due to filter passband assymetry. Commercial filters avoid these discoveries. So all of this leads me to conclude that if a new or second hand filter of known quality can be found and it it fits the space and budget, that’s a good option.

There is plenty of end -to-end gain in this receiver and the MOSFET preamp only ever gets switched in on 20m, where it is necessary. A better design may be to dispense with the front panel toggle (Preamp in/out) switch and use a control line from the Arduino to switch it in on 20m or above.

If you decide to build a slightly larger and heavier portable transceiver for SOTA or portable work, the 50 watt amp on the back end of the transmitter is a big plus. It runs for two decent activations on a 5AH LiPO and opens doors (to chasers on the other side of the world). If you end up working locals, for whom 5 watts would have been adequate, you get to enjoy the 589s and 599s coming back, they don’t have to strain to hear you, the pace is faster, the pileup is longer and deeper. A 50 watt rig is not for every activation but it has its place.

The optical encoder for tuning spins freely and is a pleasure to use. It is another luxury that you can enjoy in a bigger and heavier rig. I’ve thought about designing one of these into a compact 3 or 4 band backpack transceiver (the sort of thing you’d be happy to walk 10km with) but it is too big and heavy. The mechanical encoders don’t ‘spin’ freely but they are cheap, they draw no current, and are physically small by comparison. If you know of a quality, compact, not too heavy optical encoder that doesn’t cost a packet let me know in a comment!

Final comments

This conventional single conversion SSB/CW superhet is a fine performer on the HF bands. The use of multiple moderate gain stages and better-than-usual bandpass filtering (each with 4-poles and wound on half-inch toroids) delivers selectivity and sensitivity that compares with my Icom746Pro receiver. The options to switch in a receive preamp and a 50 watt PA add versatility.

It is compact enough to be back-packed to a summit and run on a 4 or 5AH SOTA battery. And it’s also functional enough to be used as a shack desktop. It’s not over-stuffed and therefore not too difficult to modify or repair. Overall I am happy with the design choices and trade-offs that were made.

Acknowledgements

Thanks to VK3WAC — whoever and wherever you are — for doing a fine job of building the SSB exciter in Solid State Design for the Radio Amateur. And for clearly labeling the board.

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