[hpsdr] Getting PowerSDR to display SWR

[Phil Harman]

Hi Jim,

A very interesting book and one to go on the iPad I think.

I've not yet been able to test John's work on real-time SWR display but
will do so next week.

I think the speed of acquiring the FWD and REV voltages from the ADC on
Penny(Lane) should be fast enough to display SWR in real time. We will
see...

73 Phil...VK6APH


> ***** High Performance Software Defined Radio Discussion List *****
>
> All:
>
> For what it's worth . . ..
>
> Crenshaw's book, Math Toolkit for Real Time Programming has some neat
> and efficient algorithms for all kinds of functions -- on small, integer
> computers like used to navigate Apollo to the moon.  (AND, it has some
> interesting history as well...)
>
> There might be something in there for SQRT that would allow "good
> enough" simple calculations which could be implemented in the FPGA.
> Might simplify latency/delay issues....
>
> All the best and very 73,
> Jim
> wb4gcs at amsat.org
>
>
> 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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