Topband: Re: 160m RX

[artinian]

W8JI:

> What does it matter where the noise floor is, when the upper end is
> better than anything else you can purchase? All that means is the
> receiver is very very quiet when the antenna is disconnected yet
> still has enough gain.


I wonder if God has spared Georgia of galactic noise?  If not, 10 uV sensitivity
is more then enough for 160m.  This leaves plenty of room for a good input
filtering permitting much greater input voltages close to 100V.  We only need
high level input mixers to sustain such a signals.  Pair of power MOSFET would
do but they are not commercially offered as a mixer...

> Any reduction in gain can easily be accomplished by adding an
> attenuator pad when needed, but you can't fix a overload prone or
> phase noise limited receiver with a pre-amp.

Who needs preamps on HF?  40dB attenuators come handy if RX also covers 10 m.

> > G3RPB explained the relation between IMD and phase noise in QEX letter.
> > FT-1000MP satisfies these criteria at +30dBm IMD with all the gadgets
> > added.
>
> I'm not sure I understand what you are saying by "relationship
> between phase noise and IMD" and "all the gadgets added". Was it
> a recent QEX?

Yes.  Good engineering would make RX VFO clean enough for other "linear"
circuits to saturate first.  Modern gadgets one buys these days are DSP, color
displays etc...

> My 160 meter requirements are more taxing than most other
> bands, because of the system I'm using and where I'm located. I
> have to receive some very weak signals right next to very strong
> transmitters with my antennas pointed right at the strong stations.

The whole art of HF has long been receiving weak signals close to the strong
ones.
Even the good old glowing tubes were sensitive above the outside noise on decent
antenna.  USA was blessed with a lack of BCI and only learned about interference
when many hams could afford kW amplifiers.

> Other people probably have the same situation, because first hop
> 160 meter signals are pretty strong at times...and DX signals pretty
> weak. It sure used to be better when the DX worked split!

Signal to noise ratio of DX signals didn't change much, our QRM increased a lot!

Modern VHF semiconductors technology can't help us on 160m.  Nice example is
latest FT-847 with intergrated quad FET first mixer operating on 3V DC!  This IC
probably comes straight from the mobile telephone...

Unfortunately, HF is commercially obsolete band and we are getting oversensitive
RX
intended for dummy load antennas.  They can hardly withstand strong BC signals
on 40 and 160m.  I wonder when would BBC, VOA, DLW stop?

73 de Mario, S56A, N1YU




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