Saturday, December 29, 2018

Acquiring Equipment for Cross-Polarization Operation

My future plans for EME call for me to install cross-polarized antennas so that I will be able to change my antenna polarity at will.  That way I can transmit in either vertical or horizontal polarization and also receive the same way.  No longer will I be "locked out" of making a QSO because of polarity differences between my station and the station I want to work.

IQ+ Dual RX Radio
This switchable Dual-Polarity is a pretty big improvement for me.  But, there is another level of improvement beyond just being able to switch between Horizontal (H) and Vertical (V) polarization. This is call Adaptive Polarization.  It requires a good deal more hardware and software but does an amazing thing.  It combines the Receive signals from the H and V antennas, computes the vector angle of polarization and then peaks the output according to that polarity.  This completely eliminates polarity loss.

The first piece of hardware to accomplish this is the IQ+ from HB9DRI and his company, LinkRF.  This is essentially two receivers in one box with inputs for the H and V antennas.  The two receivers are "locked" together with the same Local Oscillator (LO) so that the output from each have the same amplitude and phase of the original signal.  These outputs supply the I and Q (quadrature) signals which are samples of the same signal taken 90 degrees out of phase. 

Those I and Q signals are fed into the UADC4 (Universal Analog to Digital Converter) and then into the software.  The UADC4 is another product of LinkRF.  It replaces the PC audio cards traditionally used to interface between radios and computers.  However, the UADC4 is MUCH better than even the best PC audio card.  With the proper hardware ahead of it, the improvement can reach as much as 15 dB better performance yielding dramatic improvements in the noise floor!  (Click on images to see them larger.)

The software that does the amazing job of combining the H and V signals is called Linrad and is the creation of SM5BSZ.  Originally it was written in Linux but it is now available for Windows.  The output data stream from Linrad is sent to K1JT's Map65 software and this program provides a waterfall showing all signals in a 192 kHz passband, a WSJT type control panel for transmitting and decoding messages, plus lists of all the stations copied in the entire passband!  WHEW!

As the first step toward configuring my EME station to do all this, I have placed my order for a UADC4 and for the IQ+ revC (modified to work with the UADC4.)  I had previously pre-ordered the UADC4 some 13 months ago but it has taken this long to move the product from initial prototypes to final production.  My IQ+ and UADC4 are scheduled to be shipped about the end of January 2019.  So now I need to get the XP antennas ordered, built and installed.  Let the fun begin!

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