[TenTec] The Eagle

[John Molenda]

  Rick that was a very good explanation even I understood it !  Thanks 
for your effort .  John kb2huk

On 9/26/2010 12:02 AM, Rick - NJ0IP / DJ0IP wrote:
> Richards,
>
> (I apologize to the group; this is a very long post.  Delete it now if that
> bothers you. - Rick)
>
> It has always been the tradition that if you want to have a general coverage
> (0.5 to 30 MHz) RX, you place your first IF high above 30 MHz. (Always
> begins in the 70's.  It was different before that.)
>
> Several radios have it at 70 MHz, some at 60 MHz and a few even as low as 40
> MHz.
> The problem is, at these high frequencies, you can't build as good of
> crystal filters as you can as with filters of lower frequencies (for
> instance 9 MHz or 5 MHz, where earlier ham-band-only radios had their first
> IF).
> When I say "not as good as", that is an understatement!
>
> Basically, it is the steepness of the bandpass curve which is worse.
> This significantly affects the ultimate attenuation of the filter.
> The measurements that are affected by this are the close in Blocking Dynamic
> Range (5 KHz or less), not the wide ones at 20 KHz.
>
> Without going back to the 50's or 60's, starting in the 70's, ham band
> radios typically used 9 MHz first IF or 5 Mhz first IF (earlier ones used
> 455 kHz).  At any of these frequencies, it was possible to build 4-pole or
> 8-pole crystal filters which had very sharp (steep) bandpass curves.
> Filters at much higher frequencies had very wide bandpass curves.
> Since all of the JA sourced radios had a high first IF, with upwards
> conversion, it was thought this is the way to go.
> In doing so, you were able to build a good general coverage receiver, but
> you sacrificed ham band performance by having an inferior (broader skirts)
> first IF filter.
>
> The Orion I was the first radio to come out with a compromise.
> It used two receivers, one of each.
> The main RX had downwards conversion, which had outstanding performance
> results.
> The secondary RX had upwards conversion, which had good, but not outstanding
> performance.
> This gave us the best of both worlds.
>
> The JA companies responded with marketing, saying they had two identical
> good receivers.
> The expensive ones were very good but worse than the Orion, and they were
> certainly more expensive.
> The reason: you just cannot obtain the ultimate results using upwards
> conversion.
>
> With the Omni VII, Ten-Tec challenged the existing theory.
> You could almost say, they bent the rules.
> By paying VERY close attention to individual stage gain in the front end of
> the RX, they were able to use upwards conversion up front, then downwards to
> 9 MHz with sharp (roofing) filters at this IF.  After that, good DSP filters
> (which everyone has now days) provided the necessary sharp filtering.
> The results were surprisingly good.   Very good.  Better than we expected.
> BUT NOT AS GOOD AS A DOWNWARDS CONVERSION RECEIVER!
>
> With the K3, elecraft really bent the rules.
> They were the first ones to use downwards conversion, yet still offer
> general coverage RX.
> BUT not so fast, in order to be able to use general coverage, you had to buy
> an optional 6 kHz roofing filter AND an optional Band Pass Filter (BPF).
> THEN you got general coverage to 30 MHz... but, since it's first IF is at
> 8.215 MHz, you cannot receive signals that are close to that frequency.
> They will be drowned out by the radio's own local oscillator. That's one
> reason why they also say degraded performance on some frequencies.
>
> With the Eagle, there is no indication what the Band Pass Filters will be
> like for General Coverage.
> All I can say for sure is that it won't be able to hear well on or about 9
> MHz, because the radio's own 9 MHz local oscillator will drown out whatever
> external signal is there.
>
> Let's say Ten-Tec, for cost reasons, did not provision any special BPF for
> GC.
> Without the preselection, receiver performance degrades.
> Work-around: purchase a general coverage preselector, such as those sold by
> MJF, which were "borrowed" from the Bavarian Contest Club (without
> compensation).
> This solves your preselection problem, and all that remains is the degraded
> performance at 9 MHz.  So what?  There is nothing on 9 MHz anyway.
>
> My biggest question to you Richards, is, why do you even want a general
> coverage receiver in your main ham rig?
> There are so many tade-offs that it simply is not worth it.
> Buy yourself a good used GC RX for $300, or one of these new SDR radios for
> a few dollars more, and keep it independent of your ham radio transceiver.
> If you insist on having the GC RX within your transceiver, unless you pay
> $4000, you will have degraded performance on the ham bands !!!!!!!!!!
>
> You just can't win the Indy 500 in a Chevy Malibu.
>
> Hope this helps.
>
> 73
> Rick
>
>
>
>
>
>
>
> -----Original Message-----
> From: tentec-bounces at contesting.com [mailto:tentec-bounces at contesting.com]
> On Behalf Of Richards
> Sent: Saturday, September 25, 2010 9:20 PM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] The Eagle
>
> OK...   thanks for the uptake.
>
> Do they do this on the Omni VII ?   Reason I ask is, I am a former SWL
> interested in receiver radios before joining the ham clan, and the Omni
> VII has a great gen coverage receiver which is seems so superior to my
> previous "better" Kenwood and other SW receivers that if SW performance
> outside the ham bands is equally good on the Eagle as it is on the Omni
> VII - it will be plenty good.
>
> Parenthetically, I appreciate your taking a moment to explain these
> things, as it is a real handicap to have come to ham radio later in
> life, after a career in something other than engineering, and there is
> so   @#$%   much to learn about how these radios work.   That is the
> boon and bane of the hobby -- boon because I enjoy learning stuff, and
> bane because there is so much to learn!
> Guys like you, Gerry, Carl, Bob, Jim B, Ken, Art, and so many others
> have proven good Elmers.
>
> Thanks.
>
> ================================= JHR  ===============================
>
> On 9/25/2010 21:54, Barry N1EU wrote:
>
>> It seems a no-brainer that they're using bandpass filters for the ham
> bands.
>
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