Tree Avoidance Map for US Rovers

If you’ve ever been roving with a big dish or microwave antennas that are not on a mast, you know that locating an area without trees can be very important.  A hilltop that looks good on an elevation map is not worth nearly as much if is is covered in trees.  Most rovers survey locations in advance of operating to find out which locations are actually as good as they might appear to be on a topo map.

Scientists at the Woods Hole Research Center (WHRC) have now produced a “biomass map” (read trees) from a number of sources including the Shuttle Radar Topography Mission (SRTM) data and other data from the USGS and the USFS.  The map has 30m resolution and so presumably could help a rover determine which areas are “tree infested” and which are not (I love trees, just not when roving).  I’ve not yet had a chance to look at the real usefulness of this data down to that resolution, but just glancing at the map gives you a very good idea where densities are best and worst.

Locating trees around the US using data from SRTM, USGS and USFS

United States Biomass Map © 2011 WHRC

Clicking on the map above to enlarge it and the map on the WHRC website can be zoomed and panned for even greater resolution.

Thoughts on High RF Environments

Jim, WD5IYT, and I went roving in January again (last week) and had a blast.  We were QRV from 6m-24GHz (11 bands).  One interesting thing that happened a couple of times was a step-function shift in audio on received signals on a few bands.  Unfortunately I do not have a recording of this, but imagine if you have a VFO that tunes in 100Hz steps and when you are listening on sideband, you just click the knob a few times.  This was also heard on my transmit signal.  Apparently, RF is getting into my GPSDO — an HP 58540a (400W of 2m no doubt) and causing it to either reset or get confused about where it is.  It always quickly recovered, but this underscores the need for some shielding on the 10MHz lines running around if they will be exposed to a high-RF environment.