[hpsdr] Getting PowerSDR to display SWR

[John Ackermann N8UR]

How about taking alternate samples at a fairly rapid rate and then 
averaging over a second or two  (e.g., Fwd,Rev,Fwd,Rev etc.).  It 
wouldn't be perfect, but should improve the accuracy over just a single 
pair of samples.

John
----

On 3/8/2012 9:31 PM, Phil Harman wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> John,
>
> Preferable to do the calculation in the PC rather than the FPGA. There are
> approximations to SQRT that would be good enough for calculating SWR and
> are easy to implement in the FPGA.
>
> This should be straightforward to implement in PowerSDR. It's sure to work
> for a steady carrier but latency issues my cause a problem with modes that
> have amplitude variations.
>
> 73 Phil...VK6APH
>
>
>> HPSDR,
>>
>> I think it makes more sense for PowerSDR to do this computation than doing
>> it on PennyLane - both the Forward and Reflected Power are transmitted to
>> PowerSDR in the packet transmission.
>> (assuming the SWR cable and Alex is being used; of course.)
>>
>> Since doing fast floating point on the PC is so much simpler and faster -
>> why wouldn't we want to do the computation there?
>>
>> SWR = (1 + SQRT(ABS(Pr/Pf))  /  ( 1 - SQRT(ABS(Pr/Pf)      rho =
>> SQRT(ABS(Pr/Pf) - then
>> SWR = ( 1 + rho ) / ( 1 - rho )
>>
>> The ABS may be superfluous in this case since the ADC can't read negative
>> I
>> suppose.
>>
>> Seems simpler to do on the PC side with the current architecture.  Am I
>> missing something here?
>>
>> 73's,
>> John
>> AJ6BC
>>
>> On Thu, Mar 8, 2012 at 11:45 AM, John Westmoreland<
>> john at westmorelandengineering.com>  wrote:
>>
>>> Phil&  HPSDR,
>>>
>>> OK - took a look at the code and have some test code implemented - issue
>>> is using real #'s in the Verilog environment for the FPGA; specifically
>>> -
>>> two functions, square root and absolute value are needed to compute SWR
>>> correctly from the current hardware configuration.  Another possibility
>>> is
>>> if Voltage or Current can be extracted - then that would make the
>>> calculation simpler.
>>>  From some rough testing I did sending an SWR test value over vs. the
>>> Reflected Power - looks like it was working.  To be sure I will want to
>>> review the code for PowerSDR though.
>>>
>>> 73's,
>>> John
>>> AJ6BC
>>>
>>>
>>> On Wed, Mar 7, 2012 at 6:07 PM, John Westmoreland<
>>> john at westmorelandengineering.com>  wrote:
>>>
>>>> Hello Phil,
>>>>
>>>> If this can be implemented in PennyLane then that is great.
>>>>
>>>> I will take a look at the source and see what it will take.
>>>>
>>>> 73's,
>>>> John
>>>> AJ6BC
>>>>
>>>>
>>>> On Wed, Mar 7, 2012 at 4:39 PM, Phil Harman<phil at pharman.org>  wrote:
>>>>
>>>>>    Hi John,
>>>>>
>>>>> Your correct, we did look at this before.  From memory the issues is
>>>>> that there is a delay between the FWD and REV samples that means for
>>>>> other
>>>>> than a steady carrier the SWR reading is meaningless.  I think this
>>>>> was a
>>>>> problem with the Flex hardware but not sure if we will have the same
>>>>> problem.
>>>>>
>>>>> The solution may be to calculate the SWR in the FPGA on Penny(Lane)
>>>>> since that will have the least sample delays.
>>>>>
>>>>> 73 Phil...VK6APH
>>>>>
>>>>>
>>>>>
>>>>>   *From:* John Westmoreland<john at westmorelandengineering.com>
>>>>> *Sent:* Thursday, March 08, 2012 3:37 AM
>>>>> *To:* HPSDR list<hpsdr at lists.openhpsdr.org>
>>>>> *Subject:* [hpsdr] Getting PowerSDR to display SWR
>>>>>
>>>>> ***** High Performance Software Defined Radio Discussion List *****
>>>>>
>>>>>   ------------------------------
>>>>> HPSDR,
>>>>>
>>>>> I am sure this has been discussed before - but I can't seem to find it
>>>>> in the archives.
>>>>>
>>>>> Is there a way to get PowerSDR to display SWR on the TX Meter?  In the
>>>>> configuration settings there is a box to pick for this - but when you
>>>>> run
>>>>> there is not a way to select SWR.
>>>>> Reflected Power is there - but not SWR.
>>>>>
>>>>> Thanks in Advance.
>>>>>
>>>>> 73's,
>>>>> John
>>>>> AJ6BC
>>>>>
>>>>> ------------------------------
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>>>>>
>>>>
>>>
>>
>
>
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