Aug 082010

Well, I did some experiments this weekend regarding the bicycle mobile station using an autotransformer to match the shortened end-fed whip (6′ 27MHz helically-wound) to the 50ohm impedance my set demands.

I haven’t tried this on the bike itself… these were done in my bedro^W(ahhem) “radio shack”… with the antenna and its bracket sitting on a wooden chair connected to a longer bit of coax than I’ll probably use on the bike.  I will have to try this on the bicycle (ideally with an antenna analyser) to get a better idea of performance, and the up-coming Remembrance Day contest may provide a good opportunity to gauge performance, as the bands will be sufficiently “busy”.

The autotransformer is a simple design… about 50 turns of cheap speaker wire (~1.5mm diameter; ~0.2mm insulation thickness) on a 42mm OD PVC pipe section about 160mm long.  The pipe has small holes down its length, drilled at a spacing approximately identical to the wire centre-to-centre spacing (2mm).  The two extremes of the coil connect to the antenna and the metal antenna bracket respectively, the latter also connecting to the braid on the coax going back to the radio (about 30cm RG58C/U coax).  The centre conductor of the coax connects to a short piece of wire which is soldered to a small map pin, which is simply pushed through the wire’s insulation, piercing it and poking through the hole in the PVC pipe… I can select any turns ratio from 1:1 to 1:50, achieving a very wide matching ratio.  (On paper, able to match >10kOhm impedances to 50ohm.)

Early testing seems to indicate the ability to obtain good SWR figures on 6m, 10m, 20m and 40m.  80m (the holy grail for me) eludes me… and I suspect the actual radiated signal will be very low down to most stations… but if I can cover parts of metropolitan Brisbane with it, I guess I’m doing okay.  The fact that this antenna got down to VK5 with 100W up it, is a promising sign… perhaps with the autotransformer, it may do better.  Then again, it may do a lot worse… We’ll see.  Plan is to try and get it up and running before the ILLW… so that I can stir up some activity on the bands on my way to the Bulwer Island lighthouse (AU0003) before becoming VK4MM and operating a station there.

Aug 082010
qube ~ # catalyst -f /home/catalyst/configs/stage1.spec 
Catalyst, version
Copyright 2003-2008 Gentoo Foundation
Copyright 2008-2009 various authors
Distributed under the GNU General Public License version 2.1

Using default Catalyst configuration file, /etc/catalyst/catalyst.conf
Setting sharedir to config file value "/usr/lib/catalyst"
Setting snapshot_cache to config file value "/home/catalyst/snapshot_cache"
Setting hash_function to config file value "crc32"
Setting storedir to config file value "/home/catalyst"
Setting portdir to config file value "/usr/portage"
Setting distdir to config file value "/hd/0/gentoo/distfiles"
Setting options to config file value "autoresume kerncache metadata_overlay pkgcache seedcache snapcache"
Autoresuming support enabled.
Kernel cache support enabled.
Package cache support enabled.
Seed cache support enabled.
Snapshot cache support enabled.
Use of metadata_overlay module for portage enabled.
Envscript support enabled.

        WARNING: No value set for key cxxflags...deleting

        WARNING: No value set for key distcc_hosts...deleting

        WARNING: No value set for key pkgcache_path...deleting

        WARNING: No value set for key portage_overlay...deleting

        WARNING: No value set for key ldflags...deleting

        WARNING: No value set for key portage_confdir...deleting
Using target: stage1
Building natively for mips
stage1 root path is /tmp/stage1root
Source path set to /home/catalyst/builds/seeds/seed-20100806.tar.bz2
Caching snapshot to /home/catalyst/snapshot_cache/20100806/
The autoresume path is /home/catalyst/tmp/default/.autoresume-stage1-mipsel1-20100806/
stage1 stage path is /home/catalyst/tmp/default/stage1-mipsel1-20100806/tmp/stage1root
Resume point detected, skipping target path setup operation...
Location of the package cache is /home/catalyst/packages/default/stage1-mipsel1-20100806/
Location of the kerncache is /home/catalyst/kerncache/default/stage1-mipsel1-20100806/
Checking for processes running in chroot and killing them.
--- Running action sequence: unpack
Referenced SEEDCACHE does not appear to be a directory, trying to untar...
No Valid Resume point detected, cleaning up...
Removing AutoResume Points: ...
Emptying directory /home/catalyst/tmp/default/.autoresume-stage1-mipsel1-20100806/
Emptying directory /home/catalyst/tmp/default/stage1-mipsel1-20100806/

Starting tar extract from /home/catalyst/builds/seeds/seed-20100806.tar.bz2
to /home/catalyst/tmp/default/stage1-mipsel1-20100806/ (This may take some time) ...

And with that… a new round of stagebuilds begins… I’ll do the initial stage builds on the Qube2 for now, so things will take some time, but I want to iron out all the issues I’ve been having and get something together that builds smoothly. I may even run it through Catalyst a second time just to make sure everything is clean. These should also include the newer tools, such as baselayout-2 and eselect.

This seed stage was mostly cross-compiled on my now dead Duron. I now have a 6-core AMD Phenom II which I also plan to set up QEMU on, for stage-building purposes… and soon will get distcc going on a few of the hosts here… so hopefully I’ll have stagebuilds going much more regularly.