What is the difference between Backscatter and Batscatter ?


Some Experiments with Microwave Scattering (August 2005):


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- during the ERAU Estonian Microwave Field Day in mid-August, I went portable with 1.3, 2.4, 5.7 and 10 GHz

- the microwave part was split with 1.3 GHz on Saturday morning and higher bands on Sunday morning

- note the family sized fire extinguisher and the two thermos flasks: one for the coffee and the other for milk ;-)

- "outside" view of the 23 cm station  (dipole mat, with 50 W HB linear behind it,  TS-790R transceiver and SMPS PSU)

- the weather on Saturday was beutiful for the larger region with light clouds most of the day (view from behind the 23 cm dipole mat)

- most 23 cm QSO's were via normal tropospheric scatter and the closer ones via refraction (see Wikipedia for Snell's law etc.)

- Sunday brought heavy rain between my KP21 location and the Gulf of Finland with many simultaneous rain fronts

- needed to put a very hurried 13 cm feed together the previous Sunday for my Microwave Associates OB 120 cm prime focus dish together late Friday...

- here is photo of the heavily modified ex-1.8 GHz microwave radio now used for 2304/2320/2400/2424 MHz as installed on the 120 cm dish

- and a view of the portable setup for 13 cm (1 W RF output, NF=0.7 dB) - made some fine QSO's, one with obvious rain scatter

- the transverter is behind the dish with a short length of flexible semi-rigid to the modified 5.7 GHz waveguide feed in front of the dish

- the rain scatter was most spectacular on 5.7 GHz and with OH2AXH we had a long clean FM QSO, but boy did the S meter wiggle about !

- and finally got to 10 GHz too: my location was such, that I simply could not copy any of the OH3TR microwave OH3SHF beacons, but then things started to happen...

- got the dish round to ES2U for a pleasurable CW and SSB QSO and after this, had a go at finding the OH3SHF 10 GHz beacon via rain backscatter

- another large video file - listen to the Doppler-spread signal pitch (WARNING: file is about 20 Mb !!!) as I turn the dish around from 90 through 270 degrees

- note also the slight dish elevation required and the fact that the beacon is not copiable directly (dish pointing to the left).

- you can also see that the wind vector is approximately orthogonal to the image plane, blowing towards you as you watch the video :-)

- at this time the wind direction was approximately south-eastern, as can be testified from the Doppler shift

- the beacon - rain front - observer vector relationship (file missing still) needs to taken into account when working out the wind vector and velocity

- also made some very nice CW and SSB QSO's on 10 GHz via forward rain scatter

- all this stuff got me thinking for a change, hoping to pick up the OH3SHF beacon from my home QTH in KP21MI, so I put up my 120 cm dish in garden

- side view of the dish pointing at the top of a local mobile phone site mast giving the best reflection (dish elevation is about 5 degrees)
 
- pointing to a local mobile phone site mast gave me a dB or two of C/N from the beacon using backscatter via the passive mast refletion

- on rainy days I see enhancements from the S2 noise floor up all the way to tens of dB's over S9

- sometimes both tropo enhancement and rain scatter may be observed simultaneously with a clean carrier & doppler spread spectrum several hundred Hz higher or lower :)

- here you may find some spectrum plots, spectrgrams & sound recordings of Rain Scatter and Tropospheric Enhancement

- on most rainy days, there is absolutely no place in the garden where the beacon cannot be heard - it appears to be copiable from every direction, including downwards...

- these field tests were with my 28 cm dish, converter and FRG9600 - so I took out my homebrew converter with dish feedhorn only - still copiable at several dB C/N in the rain !

- so now I have taken out my G3JVL diode mixer transverter (my version III) from the 1980's and guess what...

- after thinking about all this for a few days, I then dug out from my junk box a 10 mW Gunn oscillator, attached a 15 dB horn &...

- not a very good recording , but here is a sample sound file, (469 kb) - there is some "static", but you can clearly hear the Doppler shifted individual raindrop echoes

- using an outside lamp radome to prevent the horn from filling up with rain to quickly ;-)  The "static" you hear in the recording above is caused by the radome.

- trying to figure a way other fellow experimenters may have a go at building a Doppler Rain Radar with a zero budget, I  modified a microwave intrusion detector

- the intrusion detector has a small feed horn with a few milliwatts of RF output and a reasonable mixer noise figure - you can also hear the swallows and bats :-) :-) :-)

- and of course a very favourable feature is that this older Racal device is pulsed and real power-miser at approx. 25 mA

- as an afterthought: rain scatter is a greatly underestimated mode of propagation - it is definitely THE mode for 10 GHz if you live between mountains or hills !

- most typical 10 GHz rain (and snow) scatter ranges are 200 - 500 km, but as recent news from our American microwave colleagues shows:

To: Microwave Reflector
Subject: [Mw] Rohde Island & Florida to North Carolina - 10 GHz Contact
21 Aug 2005 @ 2012  AF1T in FN41ee,  Rhode Island to W4DEX EM95tg, North Carolina, 1010 km via rain scatter
22 Aug 2005 @ 1836  WA8TTM in EL98cl, Florida to W4DEX EM95tg, North Carolina, 763 km via rain scatter
25 Aug 2005 @ 2301 UTC VE4MA EN19lu, Manitoba  worked KM0T, EN13vc  Iowa , 753 km via 10 GHz rain scatter
(Signals were S9 both ways on CW, SSB and FM. The QSO lasted for approximately 30 minutes with little change in signal strength.)



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Updated 05.09.2005