QRP by the Bay 4th Feb 2017

QRP by the Bay for February 2017 was held on a blistering 36 degree day at Victory Park, Chelsea Beach. As I approached it looked like about 2,000 people had come to QRP by the Bay, and many of them dragging beach umbrellas and esky’s. Looked like a ripper of a summer QRP party. Parking the car took me 15 minutes. I wondered what Peter Parker had done to pull such an impressive crowd. Alas, when I got to the hallowed tables, there were about a dozen of us, the other 1,988 people having walked blissfully past the squid pole and BITX rigs for the golden sands and cooling waters of Chelsea Beach. Their loss.

Andrew VK3BQ rode 39km on his aluminium bike to be there, a great effort on a 35+ degree day. What’s even more impressive is that after less than an hour he turned it around to ride back home again.

John VK3TVR told me about his project to build and operationalise a 70cm repeater, including making and tuning the cavities and all of the mounting design work. Others who I said hello to included Marc VK3OHM, Dave VK3ASE, Steve VK3SL, Mark VK3BES, Peter Marks VK2TPM, Mr ‘Cumes, Dan VK3FAJO, to name a few; I’m sure I missed someone, feel free to drop a comment below.

A few rigs and projects were displayed and visually devoured by the attendees. Peter Parker bought his scratch built BITX40. Peter Marks bought his compact MMR40, and there was another hfsigs.com BITX40 module and case. Peter handed out ‘gift packs’ of ceramic resonators on 4.92 and 7.2MHz, suitable for stabilising VFOs in homebrew rigs, including the VU2ESE BITX 40 module.

Ralph VK3ZZC bought his 400 watt linear amplifier using 6 x 6CM5 tube TV sweep tubes. Paralleling cheap readily available tubes for amateur service has a long tradition, I recall a US design in the 1980s for stacking 6KD6es for over a kilowatt and thrashing them to within an inch of their life. When one’popped’, you would just bin it and swap in another. The scheme works well, allowing for the fact that the paralleled plate capacitance limits the higher bands, and you need a HT supply that is relatively low (<1kV) and high current (a couple of amps). These days, the same pattern is reified in the 8 x IRF510 HF linears than some have had success with.

Everything is bespoke and much of this project is repurposed material, including the solid chassis, which houses the HT, screen, grid and heater supplies, the RF deck with 6 not so little sweep tube soldiers in two neat rows, switching and metering. The picture shows the ‘inspection hatch’ on the underneath open, revealing a dense wiring at the valve bases.  That Ralph moved it on a trolley makes its weight abundantly evident.

Of special interest to me was Ralph’s use of conical tank coils. Not Ralph’s idea but highly original none the less. I have never heard, let alone seen anyone do this. The rationale is various, but one part of it is that the turns of the inductor that are shorted out by the band switch occupy progressively less area of the inductor’s space, and therefore have a reduced impact on Q of the live inductor than is the case with conventional linear cylindrical coils. Of course, the ratio of inductance to length is no longer linear (if it ever was), it is now arithmetic according to some strange formula.  Ralph claims that conical inductors never gained popularity because no-one could master the complicated mathematics required to predict the inductance or any other characteristics. Ralph is yet to power up this beast, I am looking forward to hearing how it all works.

progressive-dev-chassis

My homebrew communications receiver, modeled after Wes Hayward W7ZOI’s ‘Progressive communications receiver’ from ARRL/QST in the early 1980), and laid out on its 1.6mm aluminium development chassis, is pictured above. More will be written on this project on this blog, when it is complete and working. I fired it up, but due to it being in the middle of the day, there wasn’t much to hear on 80 meters. It will demonstrate much better when it has the converters for other HF bands finished.

After a while, Peter VK3YE donned backpack, ankle (earth) ring and squid pole for some pedestrian/maritime mobile action in the shallows amidst the huge crowd. He got 6 or more contacts, lots of curious looks and stares, and he managed to cool cool his heels, all at once.

Most of the group convened to a nearby restaurant for a pleasant dinner. Summer QRP-BTB 2017 done, in sizzling fashion, we went our separate ways, with the thought of reconvening mid winter, in June.

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