OT2/FT1900/j-pole in the Plane
- Thanks for the thoughts on polarization - it has been considered, but the j-pole is a cheap, easy, no-drag install in the plane, and in practice it works better than predicted. The RV group has over 100 of these flying with great results using some very low power/light weight microtrak units. I previously had that a microtrak with the same antenna and did not get the dropouts that I see with the current setup, thus my question. I am running the lowest power possible on the 1900.I will make sure the audio in is disabled and see if that helps - thanks again.--
> On Jul 6, 2014, at 9:14 AM, "Pete Howell pete.howell@... [tracker2]" <email@example.com> wrote:Wow, with that many in use it could even be worth it to set up ground support (igate ) with a horizontally polarized antenna. A digi would need separate RX and TX antennae.
> The RV group has over 100 of these flying
- On Sun, Jul 6, 2014 at 8:14 AM, Pete Howell
pete.howell@... [tracker2] <firstname.lastname@example.org>
> Thanks for the thoughts on polarization - it has been considered, but the j-poleWhile the theoretical calculations are sound, as you have observed,
> is a cheap, easy, no-drag install in the plane, and in practice it works better
> than predicted.
the 20 dB hit is a non-issue when airborne. The line of sight path to
any station on the ground can easily handle 20 dB of path loss without
a problem. The j-pole antenna fits easily within the wing, and
presents a zero drag installation, with no worries about affecting
One could easily argue that people driving cars need to install their
vertical antennas on top of 60 foot poles to overcome the many dB of
attenuation caused by local LOS obstructions such as other vehicles,
buildings, and trees. By mounting the antenna 60 feet above the
vehicle many of these obstructions would be cleared, and a much better
chance of being heard by the local digis would be achieved. Of course,
there might be some vehicle performance issues, such as not being able
to drive under and obstructions on the roads.
The j-pole in the wing works well enough to provide the communications
desired, similar to a vertical mounted on a ground vehicle.
> I previously had that a microtrak with the same antenna and did not get theProgram an offset into the radio for a quick and dirty test. Make the
> dropouts that I see with the current setup, thus my question.
radio listen somewhere else, and transmit on 144.390. (ie 144.990
-600) Of course, any of these solutions makes your tracker operate in
the blind, which means you have a very good chance of clobbering other
users on the ground. When you are flying at altitude, you have a very
large outgoing footprint, as well as a large incoming reception area,
as you are most likely very aware.
As with any airborne APRS tracker, the preferred path to use is a zero
hop path. Digipeaters are designed to be stations with antennas
mounted at 100 or 200 feet HAAT (some are much higher, others even
lower) such as to provide large area coverage that can be used by
ground based assets to increase their area of influence. Those
vehicles with poor antenna height and lossy paths can only communicate
over a few miles to other similar stations. They send signals to
digipeaters to increase their area of influence to a few dozen miles.
An aircraft flying at even 1000 feet AGL will be able to influence a
much larger area than a ground based digipeater, so it really doesn't
make much sense to ask a digipeater with less coverage area to repeat
a signal that already has been heard over the whole area that is
covered by the digipeater. From the lofty vantage point of an airborne
platform, APRS trackers will generally be heard by many i-gates,
giving ample opportunity to get to the APRS-IS stream.
Pete, you're now running a very powerful APRS tracking platform. It
has many advantages over the MicroTrak for your type of operation. You
should look at setting up altitude based profile switching. You can
change your operational characteristics based on the altitude you are
at. Many people object to flying a no-hop path because they want to
use a normal terrestrial path when on the ground. This unit can do
just that. You can have a WIDE2-1 path when on the ground, and a
no-hop path when airborne. This means you get good coverage when down
low, and don't cause network congestion when up high. With the profile
switching, not only can you change your path, but also the QUIET time,
which would allow you to operate politely down low with a path, while
ignoring incoming noise and using a no-hop path up high. It looks like
you fly in an area with ground altitude around 1000 feet or so.
Program profile switching to occur about 1000 feet AGL, or at about
2000 feet ASL.
One other thing I noticed is your minimum turn time looks to be set to
5 seconds. Do you need to be updating your position every 5 seconds
during turns? It makes for a very nice track when turning on final,
but it does make a fair bit of noise on the channel. You put out 8
packets in one minute while turning from downwind to short final at
Anoka County- Blaine Airport on Friday.