Another interesting VHF tropo opening from Prague to U.K., I think it could be one of the best tropo opening since 6th November 2006. For the first time I worked Ireland via tropo with EI4DQ + EI6GF on almost 1600km and GI6ATZ heard me 419 even on 70cm (38el M2), however his power 70W was too small for 2 ways QSO [I use 10dB bigger power].. This tropo opening worked well mainly on 2m, however on 70cm I worked from UK only G8VHI and I had partial contact with G4EAT.

Some note for UK stations about VHF TR DXing from Prague

My home QTH is situated in north side of Prague some 200m next to 30m higher hill with basalt rocks and forest, so attenuation on UHF bands due to destroyed 1st Fresnels zone is huge - check picture with signal path in IO91 direction (I found that the strongest signal came from the 12 degrees of elevation):

Another problem is position of my QTH towards more remote mountains. UK, DL and PA stations have much better chance for long DX contacts due to relatively flat countries near sea which is ideal for stable formation of tropospheric ducts. However Czech Republic is surrounded on the DL/OK border by 1km [ASL] high mountains and the result is situation when "duct" is often destroyed by strong turbulence or it's elevated to higher altitude.. The usual inversion layer height in Central Europe is about 800 - 1000m ASL so it means good chance for stations on hill tops like OK1RI/OL4A, DL6NAA, DB6NT or DK1FG, however stations in lowlands have big problem to do anything. UK stations then thought that when they copy only OK beacons there isn't any activity on the band however many stations in central OK1 are cut off from condx. This is exactly my situation too. I'm some 320m ASL however 600m ASL hills are just 50km western from me and border mountains with hilltops 1200m ASL are only some 80km far.. Even I've been carefully watching Hepburn's page and weather prediction, working such a DX tropo contacts over 1000km is just like a small miracle. Better condx overview can be shown on next situation.

Every day Czech Hydrometeorological Institute (situated in south part of Prague) make 4 measurements of dew point and air temperature in vertical scale by balloon probes. Such a output of measuring from 18h UTC on 27th December can be seen at next picture.

At the graph you can see 2 main curves. Yellow curve represent the dew point temperature and the blue curve represent air temperature due to altitude in km ASL. In ordinary situation the blue curve should be constant as the air temperature decrease by altitude for some 0,65 °C on 100 m. On the graph you can see, that wet air is situated below about 1,4km ASL and dry air is higher. This thermal inversion result in good tropo waveguide ducting starting about 1,4km ASL. The duct quality for VHF DX depends on the dew point temperature's gradient, in other words the difference between wet and dry air. On 27th December I worked nice QSOs into UK however signals were weak and dxing was possible due to my EME power, my QTH was some 1km below the duct and signal had problem to get thru. Quite different situation was in case of OK0EP beacon (190km eastern) which is 1505m ASL so due to graph right in the middle of duct ! This 70cm beacon has ERP only some QRP in 5el yagi however it was heard on 27th December by several G stations on the distance around 1200km with good reports :-)

After some 15 years of DX tropo openings and after reading of several articles I realized that better condx in 70/80's were possibly causing by different climate cycle with bigger number of massive anticyclones from Atlantic. In nowadays the tropo openings are rarely longer then 1 or 2 days. What is really interesting, the thermal inversion are still almost as often as in 80's however with one big difference - without low dew temperature so we called them "dry type". Many DXers in central Europe think that it's caused by the end of communist era because after year 1990 many coil power plants were stopped by "greens".

But back to situation on 27th December 2011. The role of duct thickness to various frequencies is well known by formula

λ = 2,5 . 10^-13 . duct-thickness [m] . (duct amplitude)^1/2

mainly for usage on higher UHF bands, for an example for 2m the duct-thickness must be minimal about 130m instead of only 50m for 70cm band however how it's in the real world with 4m band?? During Autumn 2011 I tried some 4m tropo tests during better condx and heard OZ7IGY on HB9CV even louder then on 2m with 10el dk7zb (probably it's because of small attenuation from trees) and worked on 4m OZ3ZW on distance of some 550km. On 27th December I worked Russ G4PBP on 2m with quite fine signal so we QSY on 4m but nothing is heard. The same result was caused in 4m test made by OK1KT. The question is, was the angle of the duct entry too bad? Is 4m band suitable for long tropospheric contacts over mainland? Or was the unsuccessful test cause by the bad position of the duct actual position of entrance in UK (I observed very deep qsb on 2m)? If I found enough 4m stations for skeds I hope to answer such a question in year 2012.

73 & thanks all for good fun

 de Matej, OK1TEH

---------------------------------------------------------------------------

TROPO LOG from last opening

Rig:  2m FT847 + 1000W PA + 10EL DK7ZB

    70cm FT847 + preamp + 600W GI39 PA + 23EL DK7ZB

DD/MM/YY   UTC    MHz    CALL      RST     RCVD    LOC    QRB
------------------------------------------------------------------
27.12.11  13:55  144320  GW7SMV    519     519     IO81LN 1240 +MP3  400W + 12el M2, 70cm 75w
27.12.11  14:43  144257  2E0VXX/P  51      52027   IO82RJ 1210 +MP3   50W +  4el dualband 2/70
27.12.11  14:47  144332  G4EAT     529     519     JO01HR  987 +MP3
27.12.11  15:23  144195  EI4DQ     519     519     IO51WU 1591 +MP3 (recorded 23min earlier)
27.12.11  15:31  144195  G0PQO     529     539     IO92UA 1053 +MP3  160W +  9el Y  at 12m
27.12.11  15:42  144210  G7RAU     55      55036   IO90IR 1118 +MP3  400W + 12el M2 at 18m
27.12.11  15:44  144295  M0VRL     53      55      IO70PO 1361 +MP3  GS35 + 2x17el
27.12.11  16:04  144195  G4PBP     519     529     IO82WO 1184 +MP3  SSPA + 2x17el F9FT 180m ASL
27.12.11  16:11  144195  G4RGK     529     529     IO91ON 1084 +MP3
27.12.11  16:13  144195  G3UDA     559     559     IO82OQ 1230 +MP3  400W + 2x17el F9FT
27.12.11  16:14  144195  G4PBP     55      55-6    IO82WO 1184 +MP3 nil on 70 MHz, hrd on 70cm
27.12.11  16:35  144195  2E0NEY    51      55      IO81VK 1182        50W + 17el Y, IC910 his 1st OK
27.12.11  16:40  144195  G0JJG     559     559     JO02LE  970 +MP3  300W + 11el Y
27.12.11  16:49  144195  GW8JLY    51      52      IO81JM 1252 +MP3  300W +  9el F9FT
27.12.11  17:00  144285  G4SWX     57      57      JO02RF  937 +MP3  QRO  + 2x17el later 59+10dB
27.12.11  17:25  144195  GI6ATZ    559     559     IO74AJ 1466 +MP3  400W + 2x9el, 70cm he hrd me 419 @38el Y
27.12.11  17:45  144195  GW8JLY    51 QSB  51-2    IO82JM 1252 +MP3
27.12.11  17:50  144195  G8HGN     59      57-9    JO01FO  998 +MP3   50W + 2x15el CueDee FT847
27.12.11  18:02  144267  M0PNN     559     559     IO82TS 1203 +MP3   50W + 9el F9FT FT857D 10m agl +his MP3
27.12.11  18:08  144195  G4RRA     529     529     IO80BS 1301 +MP3
27.12.11  18:11  144195  G0NCE     599     579     JO01GK  991 +MP3   50W + 12el Y Owen
27.12.11  18:16  144195  G4EAT     59      56      JO01HR  987 +MP3 +NC on 70cm at 1827utc 529/439
27.12.11  18:20  432210  PA2M      599     579     JO21IP  706 +MP3 nil on 23cm
27.12.11  18:37  144292  G8TIC     59      58      IO82VF 1186 +MP3  400W + 10el DK7ZB 18m AGL
27.12.11  18:40  144264  G4KWQ     55      55      IO92AQ 1174 +MP3  400W + 2x12el M2 20m AGL
27.12.11  19:00  144195  G8GXP     59      59+     IO93FQ 1167 +MP3  400W + 12el M2
27.12.11  19:02  144195  DL6EV     559     559     JO60GQ  149 +MP3
27.12.11  19:05  144195  G4ZTR     559     559     JO01KW  972 +MP3   50W + 4x8el Y
27.12.11  19:08  432215  G8VHI     53      54      IO92FM 1144 +MP3 152# 100W 4x23el DK7ZB
27.12.11  19:20  144304  PA3FXO    55      55      JO22GD  728 +MP3 Cees
27.12.11  19:22  144304  M0RSF     55      55      IO93ES 1174 +MP3  100W + 6el OWL YAGI Chris BLOG
27.12.11  19:24  144304  DH6JL     59      56-7    JO31NI  535 +MP3 Mike
27.12.11  19:25  144302  PA2M      59      57      JO21IP  706 +MP3
27.12.11  19:27  144304  PA2DW     59      57-8    JO22GD  728 +MP3 Dick
27.12.11  19:30  144304  PD7YY     53      53      JO21WW  634 +MP3 IC910 + 4el yagi
27.12.11  19:30  144304  G6HKS     55      57      IO93OB 1088 +MP3
27.12.11  19:31  144304  PE1LWT    59      59      JO22VA  642 +MP3
27.12.11  19:32  144304  PA1BVM    59      59      JO21RO  653 +MP3 Rick
27.12.11  19:34  144304  PA3BIY    59      59      JO22HB  721 +MP3 John
27.12.11  20:00  144195  G4HGI     529     539     IO83PL 1238 +MP3 GS35 PA + 12el I0JXX
27.12.11  20:12  144245  G8VHI     59      58      IO92FM 1144 +MP3 350W + 2x9el DK7ZB Reg
27.12.11  20:22  144304  EI6GF     519     519     IO62RG 1482 +MP3 100W his 1st OK via TR
27.12.11  20:23  144304  G4AEP     559     559     IO91NJ 1089
27.12.11  20:27  144304  DL6YBF    59      59      JO31OX  548 +MP3 HRD OK0EP
27.12.11  20:36  144304  G4IDR     51      55      IO93BP 1187 +MP3
27.12.11  21:39  432200  OK2IT     59      59      JN89GF  182
27.12.11  22:13  144305  G4SFY     559     539     JO02RV  952 +MP3
27.12.11  22:47  144305  G3UKV     529     529     IO82RR 1214 +MP3 35W  his 1st OK


OK1FD    432886.0 OK0EP/B      559 qsb                     0921 28 Dec
9A2SB    432886.0 OK0EP/B      jo80objn95gm 599 AN         0907 28 Dec
DL9OLI-@ 432886.0 OK0EP/B      jo51ix jo80ob 1505m asl S4  0511 28 Dec
G4EAT    432886.0 OK0EP/B      JO80JO01 still gud          2231 27 Dec
G3LTF-@  432886.0 OK0EP/B      io91gg>jo80ob 569 1309km    2058 27 Dec
G4EAT    432886.0 OK0EP/B      JO80jo01 1174km fb          2015 27 Dec
G3YDY    432886.0 OK0EP/B      S2 and buliding             2000 27 Dec
PA2M     432886.0 OK0EP/B      JO21IPJO80OB s2 now         1951 27 Dec