A Remarkable Short Distance Aurora QSO
... interpreted by long distance field-aligned backscatter
Volker Grassmann, DF5AI
May 16, 2004
On April 3, 2004 IK2YXK (JN45OP) and HB0/HA5OJ (JN47SD) managed an Aurora QSO in 144 MHz which is worth to be examined in more detail. Analysing the backscatter geometry, this QSO was enabled by a scatter volume located above southern Germany. This result, however, appears inconsistent with the overall dx scenario on this particular day because all regions of Auroral backscatter were located at least 600 kilometers further north.
Maurizio's ("Mau") email from May 1, 2003:
Last 3 april 17.15z at 144.300 heard hb0/ha5oj/p cqing cw 9+++ without tone...there was some Au spot on clx and also in jn48 49....I was very surprise to hrd Au so strong and so close to me at my latitude...jn45op jn47sd 168km hi.
Strange becouse 1 hour b4 I was qrv .300 wid my friend ik2gso and we heard hb0/ha5khc/p cqing ssb without tone...Enrico told me Mau is Au...I was not agree..thinking a strange reflection..but while Enrico made qso I moved antenna directly hb0...no sigs....strange I thought..then he disppear...we made few comments and stop...but one hour later 17.15z heard strong cwA ...first I made qso..then when qso done I try to move antenna 330-60deg for check if reflection or really Au...well only at 10-15deg his sigs 9+++A cw left and right qtf absolutly nil!
The day later (sunday) I contect hb0/ha5khc/p and I ask about the qso wid his dexp-partner...he told they was very surpised to wrkd an Italian stn in Au..infatc ha5oj made 3time ..--.. ?? was really surprised hi....anyway he cnfm all was pure Aurora...I've sent also mp3 to some friends df7kf g7rau dk1ko 9a1cal and all says 100% au...so they told me to send file and comments to you for your studies.
Click here to download the MP3 audio file documenting HB0/HA5OJ's Aurora-type signals received by IK2YXK.
Aurora dx summary report from April 3, 2004
Refering to the Aurora summary report from April 3, 2004 distributed by PE1NWL's DXrobot service  (readers may also access the Spot Database Search at the DX Summit dx cluster ), high Aurora activity was reported in the afternoon and in the evening resulting in many 144 MHz dx QSOs in Ireland, the United Kingdom, along the North Sea coast, southern Scandinavia and, finally, along the Baltic Sea coast. From this perspective and because of the documentary audio file from above, there is no reason to assume an alternative radio propagation mode other than Auroral backscatter in this QSO.
However, browsing through PE1NWL's spotlist all Aurora QSOs correspond to backscatter locations north of, say, 52 degree latitude. No example is found, in particular, indicating field-aligned backscatter originating south of 50 degree latitude. From this perspective, the QSO between IK2YXK and HB0/HA5OJ must be considered an anomaly in the April 3 dx scenario.
Analysing the geographical position of backscatter
By using the BeamFinder analysis software , the QSO was analysed in detail, see the left hand side of figure 1. The distance between the two radio stations is only 169 kilometers resulting in a wide band of possible scatterers in the E region of the ionosphere which may all support field-aligned backscatter between IK2YXK and HB0/HA5OJ, see the green area in figure 1 (scatter positions in a height of 105 kilometers). Refering to Mau's email, the QSO was established at an antenna azimuth between 10 and 15 degree, i.e. we may estimate the scatter volume's geographical position in the south of Germany around 49 degree latitude, see the red lines intersecting the green band on the left hand side of figure 1.
Accepting this position the true scatter location, we may conclude that the April 3, 2004 Aurora band opening has developed two regions of field-aligned backscatter, i.e. the main centers of activity in the North Sea and Baltic Sea area and another spot a few hundreds kilometers further south, which appears a surprising feature though. This scatter location was apparently noticed by very few radio stations only, i.e. by IK2GSO, IK2YXK and by the operators of the HB0 dxpedition, respectively. This appears remarkable because of the high number of VHF radio stations that were all engaged in this band opening at the same time and because of the fact that IK2GSO's and IK2YXK's reports cover an observation period of more than one hour, i.e. this scatter location must not be considered a short-term phenomenon, apparently. Accepting all this, we may close this case - open questions however remain.
The author is reluctant to accept the above scenario, in fact. In the following, an attempt is made at identifying an alternative interpretation of this remarkable QSO. Refering to PE1NWL's summary report, Mau has apparently received even more Aurora signals not mentioned in the above email, i.e. he has also received Aurora signals from Reinhard, DK1KO (JO53CT) with 53A in 15 degree azimuth at 1728 UT. This appears a key information in the interpretation of the short-range Aurora QSO between IK2YXK and HB0/HA5OJ which happened thirteen minutes earlier.
Auroral backscatter between DK1KO and IK2YXK is supported by scatterers in the E region of the ionosphere extending from the North Sea to the Baltic Sea, see the green belt on the right hand side of figure 1. Refering to Mau's antenna azimuth, i.e. 15 degree, we may estimate the scatter location right above the Polish sea coast (see the line of 15 degree azimuth intersecting the green area). This result is supported by another dx spot, i.e. by DK1KO's Aurora QSO to UA3HDC at 1725 UT, i.e. three minutes before Reinhard was heard by IK2YXK he apparently worked in north-eastern direction illuminating the eastern wing of the green area.
In previous papers, the author discussed the so-called 'unusual' Aurora QSOs violating the ideal geometry in field-aligned backscatter, see, e.g. the discussion of the Aurora QSO between DL1EJA and SM2CEW  and DK3UZ and UA1CZL  and the references cited therein. In, say, 'ordinary' Aurora QSOs, the so-called aspect angle is directed perpendicular to the geomagnetic fieldline penetrating the scatter volume. In 'unusual' Aurora QSOs, on the other hand, that angle deviates from perpendicularity considerably. The largest deviation ever observed in 144 MHz ham radio, known to the author, is twenty degree (see the discussion of the DK3UZ-UA1ZCL QSO).
In fact, the Aurora QSO between IK2YXK and HB0/HA5OJ may be interpreted by an aspect angle around 80 degree, i.e. the deviation is around 10 degree compared to the ideal backscatter geometry. Considering this aspect angle, the BeamFinder analysis software now indicates many more scatterers in the E region of the ionosphere capable to support field-aligned backscatter between IK2YXK and HB0/HA5OJ, see the left hand side of figure 2. Note that this green area also includes E region scatterers located above northern Poland similiar to the backscattering between DK1KO and IK2YXK in figure 1. We may therefore speculate that Mau's oberservations (HB0/HA5OJ and DK1KO, respectively) were both enabled by almost the same scatter volume located close to the Polish sea coast.
Considering 80 degree aspect angle in the scatter geometry between IK2YXK and HB0/HA5OJ on one hand but 90 degree in the case DK1KO-IK2YXK on the other hand, does not reflect an impossible result. However, IK2YXK (located south of the Alps) would view this scatter volume under zero elevation and this is perhaps difficult to explain. Refering to 80 degree aspect angle even in the scatter geometry between DK1KO and IK2YXK, the common scatter volume moves from the Baltic Sea (see the right hand side of figure 1) in south-western direction towards the German-Polish border (see the right hand side of figure 2). The corresponding elevation is now 2 to 3 degree which appears much more reasonable than 0 degree.
Summary and concluding remarks
The Aurora QSO between IK2YXK and HB0/HA5OJ may be interpreted by 'ordinary' field-aligned backscatter (90 degree aspect angle) originating above southern Germany at 49 degree latitide. We however obtain the surprising result that this scatter volume is geographically isolated from all the other regions of Auroral backscatter which were identified several hundred kilometers further north.
Alternatively, that QSO may be interpreted by field-aligned backscatter originating above the north-west of Poland corresponding to an aspect angle of 80 degree. Estimating the scatter location at 53 degree latitude, this interpretation appears more consistent with the April 3, 2004 dx scenario than the first one. However, in this interpretation the total radio path length increases from, say 600 kilometers to 1.700 kilometers. From this perspective, IK2YXK's documentary MP3 file indicates a surprising high fieldstrength. On the other hand, Mau operates a 4CX250 power amplifier and we may assume that the HB0 dxpedition has used similiar rf power in this QSO. High signal strength is perhaps supported by another reason too: Aurora QSOs generally correspond to bistatic backscatter, i.e. the transmitter and the receiver are located at independent geographical position. The same is true in the QSO between IK2YXK and HB0HA5OJ, of couse, but the distance of 169 kilometers is rather short compared to the total path length of 1.700 kilometers. From this perspective, the radio path from IK2YXK to the scatter volume in north-western-Poland back to HB0/HA5OJ is comparable to the monostatic backscatter case (transmitter and receiver in identical geographical position) which indeed results in higher fieldstrengths compared to bistatic backscatter (the differences between monostatic and bistatic backscatter will be discussed in a separate paper which will soon appear on the http://www.df5ai.net web site).
The author considers the Aurora QSO between IK2YXK and HB0/HA5OJ an important result indicating that 'unusual' backscatter must not be considered an exclusive feature restricted to the most spectacular QSOs in Aurora dx communication. In fact, 'unusual' backscatter geometry may also enable Aurora QSOs which do not appear sensational at all. Because we cannot measure the true aspect angle in a given Aurora QSO, we actually do not know how many Aurora contacts correspond to 90 degree aspect angle and how many do not. There is certainly a number of Aurora QSOs (a high number, perhaps) which all look 'ordinary' without fulfilling the 90-degree-rule though - identifying this type of QSOs is however difficult. Apparently, we have just found an example of this type of Aurora QSOs.
Thanks for the email and this challenging dx report, Mau.