Thank you Barry for the clarification.
it would thus seem that Inrad is off base selling their “improved” Orion
filters since, as you point out, filter passband shape of the roofing filters
is irrelevant in the Orions. That “improvement” in filter shape and some slight
differences in bandwidth is all they are selling.
I was indeed aware of the filter slope selection in the DSP filters, just not
that these were the only dominant filter slope-determining factor.
We all had this discussion about A2D overload in SDR designs, maybe 6 months
ago or so. I got hammered for my statement (which I still believe), that,
without some sort of front end filtering, an A2D of only 14 bits in a fully SDR
radio cannot possibly digitize a 140+ db dynamic range spectrum of signals
without overflow. My information theory background (40 years, of using digital
signal acquisition, signal averaging and later on, some degree of DSP to
examine peak shapes) tells me that a 14 bit A2D will overflow at 84 db above
the level of the least significant bit. Dithering and oversampling can improve
this by maybe 6 or 12 db, still not enough. The experiences of the IC-7300
owners in Europe seem to confirm that notion...
Icom seems to agree with me on that since they tout their tracking preselector
in the 7610 as being intended to "eliminate A2D overflow", which seemed to have
been a problem for the 7300, which had no such preselector.
The narrow roofing filters in the Orions do the same thing, as you stated.
Regards,
Gary
PS: The problem with the beautiful Omni 6+ I got from you was the 3.9 volt
Zener diode that biases the IF, even with AGC off. it was randomly changing its
Zener potential. i found it by monitoring both the collector and emitter
current of Q2 on the AF/IF board. Both were moving in the same direction on the
digital scope screen (whereas they should have been moving 180 degrees out of
phase). The only way this could happen would be if the emitter voltage was
being moved. All other points of voltage variation had been disconnected.
Works great!
BTW: The through hole transistor from the earlier boards will not work in this
version. Since I had removed (and lost) Q3 in my troubleshooting, I learned
this and needed to get a new SMD device for replacement. Interesting quirk.
> On Mar 26, 2018, at 4:31 AM, Barry N1EU <barry.n1eu@gmail.com> wrote:
>
> The only thing the xtal filtering accomplishes in the Orion is to prevent
> overload of the ADC by off-channel signals. 4 Poles is plenty.
>
> No, the filter skirts are determined by the number of taps of the dsp
> filtering, adjustable in the Orion's menu, not by the xtal filtering.
>
> As I listed in the TenTec wiki article I linked earlier, the Orion II is
> generally a more reliable radio as they age and that's why I give it a
> slight nod.
>
> 73, Barry N1EU
>
> <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail>
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>
> On Mon, Mar 26, 2018 at 3:05 AM, MadScientist1948 <dukeshifi@comcast.net>
> wrote:
>
>> The Orion is a really great choice (either version).
>>
>> The color screen on the O2, while sort of coarse compared with the display
>> on its contemporary, the Icom 756 Pro 2 or 3, is sure a lot more pleasant
>> to use than the older monochrome displays on the O1. Also, it seems that
>> the color displays are more reliable than the monochrome ones.
>>
>> I have had maybe 10 Orion and 5 Orion 2 radios here over the years. I have
>> also repaired many of them.
>>
>> Unless I missed something, I had thought that the O2 used 4 pole roofing
>> filters while the O1 used the older 8 pole Omni 6 type filters.
>>
>> Generally, more poles provide better skirt slopes…
>>
>> Thus I would appreciate it if someone might elucidate on the reason for
>> the perception that the O2 has better filtering…
>>
>> My recollection is that Ten Tec, in their advertising for the O2 and its
>> accessories, stated that they had discovered a way to produce the filters
>> at lower cost (which was reflected in lower prices for the accessory
>> filters relative to the older filters).
>>
>> It seems to me that this “discovery” consisted mainly of using half as
>> many crystals in the filters.
>>
>> The Ten Tec’s credit, the newer filters do have shielded metal housings
>> whereas the older filters were “open air” designs, leaving some room for
>> unplanned leakage around the filters.
>>
>> Gary
>>
>>
>>
>>
>>> On Mar 25, 2018, at 9:43 PM, Michael Tortorella <w2iy@verizon.net>
>> wrote:
>>>
>>> Thank you to everyone who replied, both on- and off-list, with useful
>>> information. The consensus seems to be that performance of the two is
>>> pretty much the same, you get a pretty color display with the II and a
>>> different (maybe slightly better but not much difference in the real
>> world)
>>> filtering system. Definitely on my short list for a new xcvr.
>>> 73
>>> Mike W2IY
>>>
>>> -----Original Message-----
>>> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Michael
>>> Tortorella
>>> Sent: Saturday, March 24, 2018 11:04 PM
>>> To: tentec@contesting.com
>>> Subject: [TenTec] orion vs. orion II
>>>
>>> Hello everyone,
>>>
>>>
>>>
>>> I am thinking about jumping into the more modern world, and would be
>>> grateful for any comments from the list concerning comparing the Orion
>> 565
>>> and Orion II 566.
>>>
>>>
>>>
>>> Thanks and 73
>>>
>>> Mike W2IY
>>>
>>> _______________________________________________
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>>> TenTec@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/tentec
>>>
>>> _______________________________________________
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>>> TenTec@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/tentec
>>
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