To: | orion@contesting.com, tentec@contesting.com |
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Subject: | [Orion] Topband: BDR redux |
From: | Bill Tippett <btippett@alum.mit.edu> |
Date: | Thu, 05 Feb 2004 15:53:30 -0500 |
List-post: | <mailto:orion@contesting.com> |
Just posting a copy of this to the Ten-Tec reflectors for archive purposes. 73, Bill W4ZV Hi Jim, N2EA wrote: > What does TenTec say? S9 is 50 uV in Orion. > Does the Orion happen to have its relative AGC indicator calibrated in dBm? No, AGC Threshold is set in uV and ranges from 0.37 uV to 192 uV. AGC Threshold is the most unusual aspect of Orion since we've never had anything like it before. It determines the point at which you set AGC action to take control. If you set it too low (BTW default has been changed from .5uV to 3uV) the AGC boosts noise above that level making some think it is a "noisy" radio. In fact, what you want to do is set it at a relatively high level so that big QRN or signals don't blast your ears, yet leave weaker signals alone. Sort of like turning AGC off for weaker signals but on for stronger ones in a classical radio. The new 3uV default is OK for 10m, which has relatively low atmospheric noise, but is still MUCH too high for 160 meters. About the lowest I ever set mine on 160 is 20-30 uV, and often much higher. For example, I just checked it, and I had it set to 192 uV last night (a relatively noisy night) while listening to A45XR who went from 339 when I first heard him answer W1MK's CQ around 0030, to a genuine S8 on the meter around his sunrise at 0245. BTW, I copied his call one cycle before W1MK figured it out, even though W1-3 definitely had the propagation advantage early on.
S-Meter Actual Signal W8ZR's meas. (in dBm) S1 S9 - 44.4 dB (-117.4 dBm) S3 S9 - 30.5 dB (-103 dBm) S5 S9 - 20 dB (-93 dBm) S7 S9 - 11.7 dB (-85 dBm) S9 50 uV (-73 dBm) S9+10 S9 + 8 dB (-65 dBm) S9+20 S9 + 18 dB (-55 dBm) S9+30 S9 + 29 dB (-44 dBm) S9+40 S9 + 42 dB (-31 dBm) Source: http://dayton.akorn.net/pipermail/orion/2004-January/000191.html dBu = 20 log (uV) (referenced to 1 uV), dBm = dBu - 107 (dB above 1 uV), so S9 = 20 log (50) = 34 dBu, and in dBm = (34 - 107) = -73 dBm Assuming the typical 5 dB per S-unit, Orion's meter looks more linear than most especially below S9. It also seems stingier below S9 than my old MP. It seems stingier everywhere on 10 meters but that may be because the MP adds an additional preamp for 10 & 12 meters only. Back to Orion's AGC Threshold settings, a 20 uv Threshold is about S7+ and 192 uV is about S9+12. So I was listening to A45XR in the noise initially even though I had AGC Threshold set to S9+12. For weak signals near the noise floor, it also sometimes helps to reduce RF Gain to find the S/N sweet spot where the signal seems to separate from the noise. This is only needed in those cases where the signal is just barely above the noise level. This is why Orion's AGC takes some seat time to learn to use properly. Once learned, it is fairly easy to adjust and the AGC action is the best I've seen at keeping a wide range of signals at comfortable levels. In the CQ WW on 10 meters, it was a pleasure to set and forget it, almost never needing to ride AF and RF Gain controls like I did with previous radios. 73, Bill W4ZV P.S. I forgot to mention I use Preamp ON on most bands including 160 so that should be taken into account for the my Threshold settings (i.e. they are actually lower by whatever the Preamp's gain is). _______________________________________________ Orion mailing list Orion@contesting.com http://lists.contesting.com/mailman/listinfo/orion |
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