[TenTec] RX-340 and +30 dBm 3rd IP

[Jim Reid]

How do you use the Intercept Point spec to learn something
useful?

Ref my previous post about IMD specs and rcvr performance.
The RX-340 has as a typical 3rd order IP spec of +30 dBm.

With the noise floor as I found it on 20 meters in an SSB
bandwidth of 2.4kHz,  to be at -115 dBm today, and using the 
340 spec,  what is the expected performance to be?

The 3rd order false, spurious signals will be twice as far
below the  pair of equal ampliftude intermodulating real
signals,  as the pair of real signals are below the intercept point.
Or with the noise floor at -115 dBm,  and this is to be the
allowed level of a false signal,  then the real signals can
rise all the way up to -18.3 dBm,  or S9 + about 55 dB !
Why?

Well,  18.3 dB is one third of the way down from the specified
IP of +30 dBm of the total range of 145 dB between the noise
floor  measured down at -115 dBm,  and the Intercept
power spec'd at +30 dBM.  So,  in this case,  using the RX-340,
the spurious signal free operating range is all that way up
from -115 dBm to -18.3 dBm,  or under these conditions as
given,  a "spurious signal free" operating range of 96.7 dB !

That's nice.  But I have NEVER seen a signal that strong,
on any band out here,  hi.  WWVH,  only about 15 miles on
West from here,  with their 10 kW rigs on 2.5, 5, 10,  and
15 mHz only generate about S9 + 10 dB at the highest.  But
their phased arrays are beaming on to the far West Pacific,
so I am behind them.

73,  Jim  KH7M