"Tam/WB2TT" wrote in
:

A few years ago I bought an FT847 as a backup/VHF/UHF rig. Wish I had
spent a few hundred more for a TS2000. A friend has one, and it is
very nice if you don't mind the art deco styling.

Talking of 144Mhz (the context of the original posting)...

Competition means that all these guys claim similar SSB telephony
sensitivity (measured in a shielded room) which corresponds to an
equivalent noise temperature of about 600K.

A key issue is that on a real antenna, this 600K could easily be 6000K
due to noise created by IMD in the receiver, and that doesn't show up on
the spec sheets, you can only assess that in situ, and it varies from
receiver to receiver and antenna to antenna. (The same issue exists with
any preamp or LNA.)

Carrying on with the (slightly unrealistic) best case of a 600K receiver,
used without a preamp and with say 1dB of line loss, your receiver
equivalent noise temperature is nudging 700K which is probably adequate
unless you are in the quietest of locations.

What 'works' for someone else isn't guaranteed to 'work' the same for
everyone.

An interesting illustration was the case of one of my VHF neighbours who
had a narrow filter (of the type used in two way radio duplexors)
installed between his preamp and transceiver. I asked why that
configuration and the answer was to minimise the loss in front of the
preamp (0.5dB of filter loss would add 35K to the system noise
temperature). On my suggestion, he moved it in front of the preamp and
compared the difference in S/N on a beacon and it was noticeably better
in front of the preamp, so despite the additional 35K, it had reduced
preamp IMD noise by more than that amount.

You don't make contacts in a shielded room, don't depend entirely on
shielded room perspectives for station design.

Owen