[amsat-bb] Re: true duplex radios
vk3jed at gmail.com
Tue Jun 2 13:59:46 PDT 2009
At 05:02 AM 6/3/2009, Martin wrote:
>Hi Jim and others.
>For ordinary Repeaters the Rx/Tx in the same band is mandatory. But just
>think of the filtering needed for TX'ing lots og watts just 600kHz away
>from your Rx-frq.
>This is also the reason why most repeaters (at least that I know of)
>uses really big cavity-filters.
Either that or _very_ widely spaces antennas. For example, to avoid
the need of rather large cavities, 10m repeaters often use two sites,
linked by UHF, to separate Rx and Tx.
>But for Rx/Tx on the same frequency - Forget it. What would be the
Nice way to create a feedback loop. :D You can create an appearance
of full duplex by using a high speed switching scheme on a digital
transmission. In fact, this is exactly what happens if you run
Echolink over a wifi connection. The radio itself is half duplex,
single frequency, but the high data rate and fast T/R switching allow
full duplex for any VoIP on top of it, at the price of a tiny amount
>In my terms, a full-duplex radio is a radio that listens on one band,
>whilst transmitting on another.
Nope, full duplex refers to any communication channel capable of
transmitting and receiving information simultaneously. While I know
of no radio capable of running full duplex on the same frequency, as
someone pointed out, the humble analog (landline) telephone does exactly that.
73 de VK3JED / VK3IRL
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