Highly experimental online Rain Scatter Monitor

Closed down 10.10.2010 - needed the equipment elsewhere !


Read my bit on Rain Scatter or maybe even heard my lecture on the subject (Salo, 2005) ?

Well, the theme is very interesting and still evolving. So far the OH3TR microwave beacons in KP11VK on the bands 1.3, 2.3, 3.4, 5.7, 10 and 24 GHz have been copied in my front yard, some 67 km from my QTH in KP21MI. The 24 GHz test was run by Jari, OH3UW. All antennas have been 30 cm is diameter or less.

I often enjoy just listening to the different microwave beacons in different propagation modes; OH3SHF (6 Mb) on 10 GHz Rain Scatter and here is a longer (11 Mb) clip (22.06.2008)

Our Finnish Radio Amateur Technology Society, RATS, has a long-term project regarding an online microwave beacon propagation logger based on the ubiquitious SDR-IQ. As my QTH is not particularly good for tropospheric scatter, I am more inclined to rain scatter when not portable. Therefore I decided to make some elementary tests using an SDR-IQ and suitable downconverter for 10 GHz (my favourite band).

A typical zoomed-in spectrogram (waterfall display) of the OH3SHF 10 GHz microwave beacon looks like this (taken on July 21st, 2008) in rain scatter.

I often listen to the Finnish 10 GHz beacons mobile (!) whenever it rains - and it does at times :-) When there is rain, or snow/sleet for that matter, there is practically no place in Southern Finland were I cannot copy one of the 10 GHz microwave beacon when mobile, especially the Tampere beacon.

When I say mobile, I really mean it. At the moment, my favourite is a modified PLL Low NOise Block downconverter feeding an old modified Yaesu FRG-9600. My antennas vary from the open waveguide flange (!) or a small 3 * 4 cm horn all the way up to a "64 element dipole mat", which is really a slotted waveguide array. This I have scrounged from an old Ericsson 10 GHz radio link and is actually designed for our frequencies. When driving around, the best "hand-held" antenna inside (!) the car is usually my 9 by 11 cm horn. Typically this lies on the shooters seat or then on the console, right in front of the windshield (no heated windshields with polarisation selectivity here...)

Now then, back to the expmeriment: I have a 9 by 11 cm horn pointing to the zenith, orientation chosen so that the e-field polarisation plane is perpendicular to the beacon heading from my QTH. The horn is protected from rain by a modified plastic canister (ex-windshield carwash liquid).

So far, my comprehensive X-band waveguide selection is very non-conformal, so I have four different WG sizes I use and many more different flange types. Hence some interesting ad-hoc adaptations took place in building the 5 meter long waveguide line...my favourite being the uniquely Finnish LI-ITOS in it's Microwavers Manifestation.

Interested in the measured insertion loss of the waveguide run ? Sorry, that's "classified information" - if I told you, it would be YOU scrounging all them dirt cheap waveguide bits n' pieces at the flea market/jumble/car boot sale instead of yours truly ;-)

Some photos and links of the Rain Scatter monitoring experiment:


Michael Fletcher, OH2AUE, 10.10.2010