>
>Have any TowerTalkers built anything like this? Do high-power
>broadcasters use something like it (professionally built of course)? At
>broadcast stations I've seen some pretty big rigid coax, but never
>anything that I suspected was a shielded _balanced_ line.
>
On the transmit side at a commercial broadcast facility, they probably
design so that they can use open balanced pairs or quads. Look at the
pictures of VOA transmitters and you see open balanced pairs going hither
and yon, through phasing networks,etc. and up the bays of the big curtain
arrays. In this sort of application, you're not exactly worried about
stray signal pickup since you're sending kilowatts down the wire.
In the commercial world, the design goals vis a vis using the same antenna
for Tx and Rx are somewhat different than in the ham world. They also tend
to be regulated and/or licensed based on measured field strength rather
than transmitter output power, so they can make up some losses in the Tx
path by turning up the power knob.
On receive, where stray signals might be more of a concern (and shielded
pairs might be more useful), I suspect that they just use
transformers/baluns and coax. On a point to point link, you could hand
optimize the routing and layout of the wiring to not screw up the receive
pattern for the desired stations. By definition, you're not going to have
co-channel interference. If you need 360 degree flexibility, I suspect they
just hook up the big log periodic on a tower, and accept whatever they get.
Likewise for Tactical HF radio.. throw up a wire, let the autotuner and
amplifier take care of the rest.
Back in the glory days of the rhombic for HF teleprinter links, did they
use the same antennas for Tx and Rx, and if so, how did they do the feeds?
Big stations, like Portishead radio in the UK (now QRT), actually separated
the transmitters (at Rugby, Warwickshire) and receivers (Somerton,
Somerset) by many miles. However, if you were on some island in the
Pacific, for example, how did they do it (e.g. Guam to CONUS links)
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