[Elecraft] XTAL AND DSP simply is the best design

[Larry Phipps]

I remember I had one of the first of those external rf clipper 
processors about 20 years ago... it was called Com-something. They used 
an "if" of about 50 kHz, with LC filters... it worked amazingly well and 
was sought after by DXers and contesters.

Larry N8LP



WA2JJH at aol.com wrote:

>You look at the TS-870, 746pro, and many other DSP rigs all make the same  
>stupid design flaw.
> 
>  Dual conversion DSP!  No multiple pole xtal filter.
>No computer algorythm can emulate a multipe pole IF filter. These are your  
>$2000-$3000 rigs
> 
>  The TS-850 had dual xtal IFs. However there was much junk from all  the 
>CPU's and yes up conversion, then downconversion and demod after the 2nd IF  
>filter adds to the noise floor.
> 
>  How the R-7A did it was interesting. A 4 pole Fixed Xtal filter  followed 
>the upconverter.
>It has a pass band of 12kcs. That's right a 12Khz wide IF. This gives this  
>collectors radio
>its used price tag of $2000. The 2nd IF used those 8 pole can  filters.
> 
>  I found the K-2 has crystal clear SSB with the 1.8khz filter  position. The 
>R-7A the SSB gets muffled at 1.8khz. I use 1.8 khz only on the K2.  The TR-7 
>used a 2 pole filter after up conversion. 
> 
>  If you look at the schematic of the TS-850, you see the dual IFs are  in 
>the back of the receiver. So after upconversion the passband is 50kc wide.  That 
>is a large window for synth junk to get in. HOWEVER IF YOU USE CW filters  in 
>both IFs, your CW reception will be as good as a K2
> 
>  The K2 wisely put much non xtal filtering right after the antenna  jack. 
>The band pass filters are wide enough for the Ham bands and very little  general 
>coverage. You lose general coverage ability of an R-7A. However do  you 
>really need a short wave rcvr in a ham rig?
> 
>  So yes one can compare the K2 with up to $3000 dollar rigs.
>However on SSB TX the K2 comes up average. It is average because the SSB  
>adapter is a simple design. The all important audio chain is mostly in 2 chips.  
>However I always get good audio reports. A RF proc of the TS-850's design 
>would  make the K2 rock.
> 
>  There is a cheap way of doing this. There are a few speech procs  that go 
>between the mic and rig. They are true RF procs. Your audio is up  converted to 
>500kc. The 500Kc RF is processed by using an AGC like amp. At the  RFstage 
>more compression can be used with out AUDIO DISTORTION. Any RF clipping  by 
>products are filtered out. The DSB signal is then down converted back to  audio 
>with the exact same phase it entered the device.
> 
>  So one is feeding in audio that was RF processed. One can use up to  12db 
>of RF processing. Audio processing gets distorted after 6db. One company  makes 
>this device for $60. It can be put in the mic or in the rig.
>   I am ordering one. I will give on air checks for those that  want too.
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