[CCF] FW: [CQ-Contest] receiver evaluations

[jukka.klemola at nokia.com]

Eric has kind of a technical, but important point !
The main point is not technical.
Main point is we should insist on having better receivers
but companies making receivers are not taking the requirement
seriously.
Maybe we need to show the need better. That task is not easy.

73,
Jukka

> -----Original Message-----
> From: ext Eric Scace K3NA [mailto:eric at k3na.org]
> Sent: 20 March, 2003 01:31
> To: al_lorona at agilent.com; cq-contest at contesting.com
> Subject: RE: [CQ-Contest] receiver evaluations
> 
> 
>    Well, actually, I think that contest conditions are very 
> similar to the NPR test.  More particularly, the NPR test is 
> a far more
> accurate representation of what's happening on the band 
> during a contest, compared to a two-tone test with just two 
> signals on the
> band!
> 
>    And while some of our current receivers might look pretty 
> awful, designers aren't going to work on improving them until they see
> some market interest.
> 
>    Thanks for all the good info, Al!
> 
> -- Eric K3NA
> 
> -----Original Message-----
> From: al_lorona at agilent.com [mailto:al_lorona at agilent.com]
> Sent: 2003 March 19 Wednesday 13:39
> To: eric at k3na.org; cq-contest at contesting.com
> Subject: RE: [CQ-Contest] receiver evaluations
> 
> 
> 
> One more thought...
> 
> The NPR test applies best when the interfering signals are on 
> all the time, all at the same time. This would be the case in, for
> example, a cable TV system, or a satellite downlink system. 
> That's what the notched noise is trying to replicate.
> 
> In a ham receiver, the interfering signals aren't usually on 
> 100% of the time (in other words they have a duty cycle less than
> 100%), and they aren't usually packed solid across a band-- 
> although a crowded contest is the closest we come to that condition.
> Therefore, the NPR test would really be a 
> much-worse-than-worst-case test, and we would probably be 
> appalled by the measurement
> results of our receivers.
> 
> The NPR signal really re-creates the conditions that we would 
> have if every ham in the world picked a different frequency on 20
> meters (except for 14.025 MHz) and then went key down for 60 
> seconds while you tried to listen for a weak signal on 14.025 MHz. Can
> you imagine? Not very realistic.
> 
> Regards,
> 
> Al  W6LX
> 
> 
> -----Original Message-----
> From: Eric Scace K3NA [mailto:eric at k3na.org]
> Sent: Tuesday, March 18, 2003 1:06 PM
> To: Cq-Contest
> Subject: [CQ-Contest] receiver evaluations
> 
> 
>    For some time now, ARRL and others have included in their 
> collection of receiver performance test the blocking dynamic range and
> two-tone 3rd-order IMD, using two signals with some spacing 
> such as 5 or 20 kHz.  Of course, two strong signals doesn't 
> emulate much
> of the real world.
> 
>    I recall a variation of this test that was used by AT&T to 
> evaluate performance of multi-channel radio receivers used to carry
> large quantities of telephone channels.  Naturally, one did 
> not want a strong signal in one telephone channel to contaminate the
> signals being carried in other channels on the route.  The 
> test was performed as follows:
>    -- instead of two signals being applied to the receiver 
> under test, a broadband noise was applied.  The noise was modified by
> notching out the bandwidth for one channel; i.e., essentially 
> no noise in the notched channel.
>    -- measurements were made in the channel corresponding to 
> the notch.
>    -- noise power to the receiver was increased until the 
> point at which the measured channel started to exhibit 
> degradation (e.g.,
> increase in the noise floor).
> 
>    This seems to be a more general test that corresponds more 
> closely to what a contest receiver experiences on a crowded band;
> i.e., LOTS of signals attacking the receiver across the band.
> 
>    Could those who are knowledgeable about receiver 
> evaluation methodology comment as to whether such a test 
> would be more likely to
> accurately characterize the ability of a receiver to hold up 
> against strong signals outside of the operating passband than the
> two-signal test method?
> 
>    Thanks.
> 
> -- Eric K3NA
> 
> 
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>     The world's top contesters battle it out in Finland!
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> ---------------------------------------------------------------
>     The world's top contesters battle it out in Finland!
> THE OFFICIAL FILM of WRTC 2002 now on professional DVD and VHS!
>        http://home1.pacific.net.sg/~jamesb/
> ---------------------------------------------------------------
> 
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