> I notice in the below referenced article on antenna
> separation that it is stated that the "graphs are misleading
> and no where near accurate for modern day solid state equipment".
> That is not correct as the graphs for antenna isolation show
> approximately how much isolation can be expected with a given
> amount of separation either vertically or horizontally. This
> has nothing to do with the amount of isolation NEEDED for
> proper duplex operation.
I think the author(s) who wrote text in that article were thinking of the
duplex isolation curves (such as the ones published by GE), not the antenna
separation curves that followed in the article. Those curves are published
elsewhere on the site; maybe a link to them should be in the text.
Regardless, measurement of isolation is a lot more accurate and reliable
than using graphs. For two co-located antennas, it's easy to from one to
the other to measure the actual isolation. For distant antennas, path
models and/or free-space calculations are easy enough to do from behind the
desk, or do RSL measurements while transmitting using a calibrated test
signal from the opposite site.
> As another note in the article it suggested using a spectrum
> analyzer to tune the receiver's local oscillator chain for
> lowest noise. While that is one approach, an easier and
> probably more accurate way of doing it is to use a sinadder
> on the receiver while tuning it up. Tuning everything for
> best sinadd will result in best signal to noise performance
> of the receiver which would also include lowest noise out of
> the local oscillator chain.
While you might be able to eek out a fraction of a dB more sensitivity by
peaking the LO for maximum SINAD (which would likely be the point at maximum
LO injection), without looking at it spectrally, how can you tell whether or
not the LO is spurious? A spurious LO, especially one that comes and goes,
is a miserable situation. You're better off tuning the LO multiplier stages
by following the factory procedure, especially if you don't have a spectrum
analyzer available.
> I hope I don't step on any toes here.
Those of us that have been on here a while wear steel-toed boots. They're
good for both defense as well as offense :-)
--- Jeff
