[TenTec] Orion AGC setting for QRN

[Bill Tippett <btippett@alum.mit.edu>]

Hi Mario and Sinisa,

        A few coments below (*****):

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

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

*****The original context of this subject was for strong atmospheric QRN
(from lightning), and I agree with Sinisa that no noise blanker works for
noise of this nature.

QRN is random short but very strong pulse.

*****This is more like very short electric fence pulses ("tick...tick") and
most NB's are very effective for this type of noise.  For electric fences
(in USA) that cycle high voltage 60 Hz on and off at about a 1 Hz rate, no NB
I have ever used seems to be effective.  Of course 99% of the time I keep
NB Off because it destroys any RX front-end if there are strong signals nearby.

>> 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!

*****I read G3SJX's review of Orion in the June issue of RadCom and noted the
following comment:

"The close-in results with the narrower roofing filters are very impressive
indeed, results with the 2.4kHz filter being significantly better than with
the 1kHz filter."  (Published table shows 5-6 dB better at 1-4 kHz spacings).

This was very curious to me since all other tests I've seen (ARRL, YT1NT,
Sherwood and W8JI) indicate that the 1kHz filter has the best dynamic range
performance.  G3SJX was very complimentary,  but I'm left wondering if the
1kHz filter in the unit he tested may have been defective.  If so, he may
have measured even better results with a different 1kHz filter.  Which raises
another bothersome issue for difficult-to-measure performance characteristics
such as Phase Noise, IMD, BDR, etc.  How do we know if our unit is working
properly or not?  This is a common issue for all radios and not just Orion.

                                                73,  Bill  W4ZV



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