[linrad] RE: Daydreaming

[Leif Asbrink <leif.asbrink@xxxxxxxxxxxxxxxx>]

Hi Stan,

> But, what direction are we going in, with the TX side ?
The way I plan to go is to use two Tx cables, two power 
amplifiers and two driver amplifiers.
At a tx power level in the order of 1 W I will add
a phase shifter and then feed the two sides with equal
power from a hybrid and combine the powers from both
amplifiers in another hybrid.

To start with, the tx will be any old tx that is available.

This will give linear polarisation with full freedom to
set the polarisation angle.

I may add two relays to be able to make one of tha cables
0.25 wl longer so I can have circular also.

> If the TX DSP signal is to be generated from a PC/Soundcard, we will 
> have to up convert to the operating freq
> and separately feed the linearly polarized V and H antennas.
Not a very good idea. I want both power amplifiers at full power 
for all polarisations so they should be combined as the last step.

It will be silly to use a dual converter chain just to set the
phase. The tx problem is different to the rx problem and the same 
solution is not the optimum one.

> With 2 separate TX channels, components will be 2 X as expensive as they 
> are now.
There will not be much difference:) Two good power amplifiers that are 
combined is not necessarily more expensive than one amplifier for twice 
the power.

The phase shifter and hybrids cost next to nothing.

> I am trying to think of alternate approaches to get a polarization 
> variable signal more suitable for EME or terrestrial comms,
> without the expense of 2 separate TX systems, 1 for V and 1 for H.
> 
> Possibly if I could power divide the TX output into 2, one going 
> directly to one antenna polarization and the
> other split going to a electrically tuned phase shifter. The phase 
> shifter being controlled by a PC/Soundcard.
Yes, here we are - but I will control the phase via the parallel port.

> What are others proposing to do for the most improved TX side  ??
Maybe, some day I will make the TX2500, TX10700 and so on. 

 
> What would be the result of feeding a RHCP and a LHCP signal from a 
> septum feed to the 2 RX channels  
> and down converters for use with  LINRAD  ??
Exactly the same as when you feed Linrad with any other pair of
orthogonal antennas. The polarisation indicator will show circular
when the received polarisation is linear and vice versa, otherways
there is no difference, Linrad will find the optimum polarisation.

(When somebody needs it I could add a parameter for this in the pol
setup so the indicator will display the correct polarisation.)

73

Leif

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