[TenTec] Orion AGC setting for QRN

[Marijan Miletic, S56A]

OC Pirotjanac, YT1NT didn't read Collins book on HF SSB carefully enough :-)

>> The proper tool for QRN fighting is N_oise B_lanker.

>Not on most contemporary receivers,
>including Orion and MkV.  Pulsewidth?

QRN is random short but very strong pulse.  If it is allowed to go thru
comlete RX chain to AF, it would be streched a lot due to the ringing of
narrow IF filters.  NB is used in wide first IF in order to prevent just
that happening.  Both MkV and even Orion have 20 kHz wide filters followed
by NB.  That BW doesn't affect QRN pulse width so blanking is very
effective.  It is also adapted to the psyhology of hearing as we do not
detect missing sounds!  Once upon a time of Cold War, NB was the only way to
reduce (repetitive) QRM from Russian Over_The_Horizon_Radars.  Even today my
FT-1000MP has two NB settings...

>> AGC should not repond to short pulses at all.  Unless it protects DSP A/D
>> from overflow.

>Unfortunately, most AGC systems are peak-responding.

Yes, they are but designed for controled, bandlimited signal peak power
change, not for QRN crashes!


>> W8JI RX IMD measurements with 10 kHz spacing seems to be USA tailored.

>In what sense?

First IF filters are usually 15 kHz wide and you can squeeze both 10 kHz
spaced test tones to make life difficult for second mixer.  20 kHz spacing
is much easier case.  Only Orion and K2 use narrow front end IF filters
until expensive IC-7800 and FT-9000 showed up.  Their high BDR claims shoud
be always checked against image and IF rejection which is within operating
frequency range!

73 de Mario, S56A, N1YU