[hpsdr] Penelope's progress

[Murray Lang]

This list is going to be a great resource for people like me who are 
hoping to understand it all a bit better before they die.
 A "best of" collation from this list into a single download would be 
nice once everything gets through the wash. Perhaps even a book is in 
order eventually?

Was that a wince?

Many thanks,
Murray VK6HL

Robert McGwier wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Phil Harman wrote:
>   
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> I now have the Alpha prototype of Penelope running and producing RF out.
>> Lyle, KK7P,  did a great job of laying out the PCB and kitting for the 
>> prototypes -
>> many thanks Lyle.
>>
>> My experience with the prototype, and the experiments on the  preselector
>> (Alex) that I have been doing with Graham, KE9H,  have resulted in a change 
>> in
>> architecture for Penelope (and Mercury).
>>
>> The reason for this is as follows.  We had intended to allow the use of  the
>> LPFs from Penelope as front end filters for Mercury and/or QSD etc based
>> receivers.
>>
>> In testing various filters for Alex what I found was that for receivers with
>> a potential IP3 of  +50dBm one needs to be very careful as to  the choice of
>> inductors used at the front-end if one is not to significantly degrade the
>> IP3 performance.
>>
>> I now fully appreciate why the German Hilberling PT8000A  receiver uses a
>> massive 2" diameter  T200-2 toroidal inductor in its preselector.
>>
>> See the photo of the preselector here
>>
>> < http://www.hilberling.de/produkte/produkte_pt8_t9.htm >
>>
>>  Even with such a large core I can detect a slight degradation in  IP3 
>> performance when using a
>> T200-2 inductor as apposed to an equivalent air cored inductor.
>>
>> The bottom line is that whilst we could  make LPFs for Penelope that will
>> provide adequate harmonic attenuation, given the size constraints of the
>> Penelope PCB, the IP3 performance of a high performance receiver will be
>> noticeably degraded if we use these filters on receive also.
>>
>> We have found the same IP3 issues with the HPF's and LPF on the Mercury
>> front-end - the small SMD inductors are simply not good enough for a 
>> receiver
>> with such a high IP3 performance.
>>     
>
>
> ---- snip ----
>
> I just want to caution everyone that it is almost trivial to get 50 dBm 
> IP3 with my old Heathkit HW8 without modification to it.   I put a 70 dB 
> attenuator in front of it!
>
> What matters in a receive SYSTEM, is THE ENTIRE SYSTEM.   If the Linear 
> Technologies through the Cyclone presents a 60 dB noise figure, and it 
> takes 40 dB gain to get a usable NF,  then a 50 dBm IP3 just became 10 dBm.
>
> We need to be careful with claims until the SYSTEM AS A WHOLE is measured.
>
> That caution stated, my calculations and simulations show say that with 
> usable gain  the Mercury is going to be excellent, possibly even world 
> class.  How excellent will be determined by implementation details (as 
> is clear from Phil's fantastic note) and it must be measured to be sure 
> and measurement at one frequency is not enough.
>
> ---- back to our regularly schedule program ----
>   
>> I will update the Wiki shortly to reflect the changes we have made.
>>
>> 73's Phil...VK6APH
>>
>>
>>     
>
> 73's
> Bob
> N4HY
>
>
>
>   


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