Polarisation diversity reception on 50MHz

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Historical recordings

[page updated 02 Sep 2016]

See my Diversity presentation given at G3WOS BBQ 08/08/2015 (pdf, 1.8MB)

Here are some recordings of dx heard here in IO81QC on 6m using polarisation diversity.   Polarisation diversity is often used on the LF and HF bands where it can contribute significantly to the readability of the signal. (For recordings of its use on other bands, see for example the websites of EI6IZ or N1EU or W8JI)

The recordings here are in mp3 format in stereo with 11kHz sampling, the left hand channel being horizontal and the right being vertical polarisation.  The recordings are best heard using stereo headphones.

Date dd/mm/yyUTCContentkmPropagation modeFile sizeDurationComments
NEW!
2015 season




14/05/15
1529
3B9FR in MH10rh
10144
F2 +Es?
373kB
47sec
Diversity working LZ2DF. Strong and then fades out.
14/05/2015
1516
3B9FR in MH10rh
10144
F2 +Es?
696kB
1m 29s
Diversity working G3ZSS and me.  Very weak on vertical.
02/05/2015
1310
ZS4TX/6 in KG47ur 8745 TEP + Es 275kB
35sec
Diversity, working G4FJK.


2014 season




24/09/14
1901
ZS4TX/6 in KG47ur
8745
TEP + Es? (no Es evident though)
2460kB
5mins
Diversity but very weak on vertical. Rapid phase shifts between H nd V.
23/06/14
1928
ZD7VC/B in IH74
7456
Es + TEP or nEs?
679kB
1m 27s
Slightly rough sounding note, with phase changes typical of Es
05/04/14
1643-1647
C5YK in IK13pk
4373
F2
671kB
1m 25s
Diversity in ssb with gaps edited out. Quite fast phase changes between H and V.
04/04/14
1621
TZ6BB in IK62ao
4305
F2
309kB
39s
Diversity in ssb, working G4FJK. Fairly stable phase shift between V and H.
04/04/14
1552
TZ6BB in IK62ao
4305
cw, F2
238kB
30s
Mono only, working me.
20/03/14
1511
6V7SIX/B in IK14lk 4274
F2
424kB
54s
Diversity.  Beacon with slowly drifting phase between H and V.


2012 season




02/06/12
1627
6O3A in LJ29an
6261
cw, Multi hop Es 456kB
58s
Mono only. Working G4PWA
15/05/12
1549
FR4NT in LG79pa
9792
Es + TEP
315kB
40s
Diversity.  Working G5WQ who is audible by backscatter as well as direct
05/05/12
1720
Z21BB in KH52ne
8333
cw, Es + TEP
287kB
37s
Mono only.
09/03/12
1123
6V7SIX in IK14lk
4274
F2
610kB
1m 18s
Diversity. Remarkably stable with virtually  constant phase shift between H and V


2011 season




23/10/11
1701
6V7Q in IK14LL
4270
F2
648kB
1min 22s
ssb. Much slower fading and more correlation between H and V than Es propagation
21/10/11
1706
3XY1D in IJ39dl
4735
cw, F2
626kB
1min 20s
cw cq.  Ditto
26/09/11
2147
GB3LER beacon in  IP90jd
1008
Auroral-E
545kB
1min 09s
Rapid flutter, stronger on h pol
26/09/11
2131
OY6BEC beacon in IP62oa
1239
Auroral-E
999kB
2min 07s
Rapid flutter, signal strong on both polarisations
26/09/11
1713
LA8AJA in JP50hp
1338
cw, Aurora
566kB

Mono only - 57A
25/09/11
1645
5N7M in JJ39sb
4763
cw, F2 - 1st qso on 6m F2 for 9 years.
544kB
1min 10s
Mono only - weak signal. 559 then fades out.








16/06/11
2023-2028
PJ4E in FK52ud
7264
cw, Multi hop Es 2MB
2min 10s
Edited highlights - working G3WOS, GM3WOJ, G4RRA, G3TCT
18/06/11
1335
TF/DL3GCS
in HP93dt
1800
cw, Es
1.3MB
1min 22s
Working G4EZT.  TF/DL3GCS was using a vertical antenna.
18/06/11
1416
VO1FU beacon in GN37ol
3587
Multi hop Es
491kB
31s

25/06/11 1656
K1TOL in FN44vg
4935
cw, Multi hop Es
967kB
2min 4s
Channels swapped: LH=Vert, RH=Horiz. I am transmitting on the vertical.
27/06/11
1930
PJ2/DJ9ON in FK52lf
7308
cw, Multi hop Es 591kB
1min 16s
with QRM
30/06/11
1834
PJ76 in FK88
6399
Multi hop Es 551kB
1min 10s
ssb wkg G0VQY
30/06/11
1942
PJ76 in FK88
6399
cw, Multi hop Es 513kB
1min 6s
cw split in mono, working M0BKL, G3TCT

01/03/11
1800 approxMM0AMW in IO75ej 516cw, Aurora444kB57sworking G4WJS - audible by both Ar and direct










2010 season




08/04/101243CS5BLA beacon in IM57px1534Es356kB45sEarly in Es season.
25/05/101650A92IO in LL56fe5223Multi hop Es553kB1min 10sworking split, intervals between transmissions edited out
25/05/1017171B1AB in KM65pi3345Multi hop Es624kB1min 20sin QSO with G0CHE
04/06/101633A92IO in LL56fe5223Multi hop Es225kB29sworking me
05/06/100821E4X in KM71oq3758Multi hop Es465kB1 minworking split up 5
10/06/101918FY1FL in GJ35qd6873Multi hop Es398kB51sworking me
22/06/101507A71EM in LL55rj5356cw, Multi hop Es485kB1min 2sWorking me, mono recording only
22/06/102041JW9SIX in JQ94lm2784Multi hop Es361kB46sBear Island beacon, vertical ant
24/06/100845ST2AR in KK65er5009cw, Multi hop Es465kB59sCallers not being heard
28/06/101612FS/W6JKV in FK88 6354cw, Multi hop Es519kB1min 6sWorking G5WQ
28/06/101619FS/W6JKV in FK886354cw, Multi hop Es426kB54sWorking me
30/06/102035JW7QIA in JQ68tb3067cw, Multi hop Es446kB57sWorking me, mono recording only
19/07/101924YO4RYU/MM in IM38dh1665Es415kB52sRecording with AGC off. G0JHC heard via backscatter on both pols, and others calling heard on V pol.
19/07/101946CS5BLA beacon in IM57px1534Es712kB1min 31sRecording with AGC off. Breaks in RH channel caused by me checking sub rx. 3 second period sinusoidal fading evident.
05/08/101457GB3LER beacon in IP90jd1008Es290kB37sShort skip Es, recorded with AGC off
05/08/101505GM8LFB in IO88kk815Es346kB44sShort skip Es, AGC on
06/08/101339N3DB in FM18su5707cw, Multi hop Es351kB45sworking me


In general the signals (which started out as horizontal polarisation*) show a significant vertical component.  Very rapid changes in the H-V relative signal strength are evident, even several times a second.  There are some instances of the vertical signal being much better than the horizontal.  The signal from G0CHE (tropo, 139km) is only heard on H pol.  It will be interesting to see in the next few years whether signals via F2 propagation show similar characteristics.
*except JW9SIX - vertical

The 3 second period sinusoidal fading of the CS5BLA beacon on 19/07/10 can be seen here (screen shot of Audacity, upper trace is LH channel = H pol)
Audacity screen shot of CS5BLA beacon

The effect we are seeing is called "Faraday  rotation".  In the ionosphere and in the presence of the earth's magnetic field, the linearly-polarised wave from the transmitter is split into two essentially circularly-polarised waves (called the ordinary and extraordinary waves) with opposite senses of rotation.  (Note that a linearly-polarised wave can be defined as the vector sum of two circularly-polarised waves.)
LH circular polarised wave  RH circualr polarised wave
Left hand circularly polarised wave                              Right hand circularly polarised wave

The two waves in the ionosphere have different wavelengths and phase speeds.  Therefore, the polarisation of the resultant linearly-polarised wave appears to rotate (Faraday rotation).  The effect came to prominence when the first satellite transmissions on frequencies from 20 to 136MHz were received on the ground. The characteristic fading appeared as a rectified sine wave with deep nulls, similar to that seen here.

The rapid changes in received polarisation can be demonstrated rather well using an oscilloscope with one channel fed to the x axis and the other to the y axis. This can be achieved very simply on a PC by downloading and installing "Soundcard Oscilloscope".  Open the scope and then play the mp3 file - I use "realPlayer".  Select X-Y Graph on the scope and see the effects visually!

Or see a quick video of the effects here (37sec, .avi format, 6MB).  This is the GB3LER beacon as recorded above on 5 August 2010, range 1059km.

Lissajous figure of JW9SIX beacon

Equipment used

Elecraft K3 with subreceiver in diversity mode - see my K3 page.

Recordings - made with a Zoom H2 recorder, uploaded and then edited and processed with Audacity to produce mp3 format.

Antennas used - 5 ele M2 yagi for H Pol and a dipole with reflector for V Pol - the dipole and reflector are mounted on the 4m yagi above the 6m yagi.

yagis and vertical dipole
The calculated gain of the M2 yagi as installed is 9.2dBd. The calculated gain of the dipole with its reflector is 2.8dBd.








 


 








Further reading and interesting links

"The enhancement of HF signals by polarization control" B Sykes, G2HCG Practical Wireless November 1989 and reprinted Communications Quarterly November 1990.
This article is interesting because G2HCG displayed the output of each antenna (3 element yagis in X formation on 28MHz) on the two channels of an oscilloscope, rather as described above. He concludes that the polarisation of the transmitted signal is irrelevant; that the received polarisation is controlled by the ionosphere; and that most fading is caused by polarisation changes.

SM5BSZ's main website includes a lot of discussion on the use of diversity to work 144MHz EME. Here you will find a lot of useful insight into polarisation control, calibration, antenna design and so forth. There is also a UK mirror site.

KL7UW's website describes his system for 144MHz EME work using polarisation diversity.

General discussion of circular polarisation.

Polarisation of auroral backscatter at 50MHz

In working stations by Auroral backscatter, it is interesting to speculate whether a polarisation diversity receiver might offer some advantage in improved signal to noise ratio. Auroral backscatter occurs in the E region of the ionosphere where ionised particles move along lines of the geomagnetic field. The scattering from such field-aligned particles requires a particular geometry between transmitter and receiver, and this has been covered elsewhere in detail.

A search of the academic literature online reveals a number of experiments, some early ones in 1954 as well as more recent work eg Ref 1. This reference includes some interesting visualisation of the received signal polarisation and its variation over quite short periods of time.

There are two rather nice graphs showing first a highly polarized return, and in the second an almost completely depolarized one.

Here is their diagram of a strongly polarised return at 0430 to 0435UTC

Strongly polarised Ar return

They interpret the strongly polarised return as implying

...a small scattering volume and/or a small number of discrete scatterers located close to one another...

Here is a depolarised return at 0345 to 0350UTC on the same day – ie 40 mins earlier.

Depolarised Ar return

They interpret this to mean that the depolarized wave is
...coming from a number of individual scattering volumes within the scattering region (i.e., the effective radar viewing region), which are each influenced differently by Faraday rotation to and from the scattering region

How does this help us to work Aurora on 50MHz? It means there can sometimes be benefits in using diversity reception but this will not perhaps be typical.

Ref 1. Polarization of auroral backscatter at 50 MHz  G. C. Hussey, J. A. Koehler, and G. J. Sofko; Radio Science, Volume 32, Number 2, Pages 541-555, March-April 1997