[TangerineSDR] Notes from PSWS / TangerineSDR call of 12-02-2019

[Phil Erickson]

Hi Tom,

  You've already convinced me that people are thinking about the issue, so
that's great.  I do agree that the AM BCB filter is quite a mess!  It
points out the general need for a good calibration procedure in general for
the TangerineSDR.  It will take some careful thought to understand what
needs to be characterized and how to do it, which presumably will be part
of the package during assembly.

73
Phil W1PJE

On Tue, Dec 3, 2019 at 2:14 PM Tom McDermott <tom.n5eg at gmail.com> wrote:

> Hi Phil - Attached is the group delay (red curve) for the AM BCB filter
> with exact component values.
> The real filter will be different slightly due to available inductors are
> slightly different values
> than the calculated inductors.  Note the delay is about 100-1000 times the
> values from the LPF.
> This is due to the need for poles at 500 kHz for the bandstop filter,
> those have of course much more
> effect.
>
> -- Tom, N5EG
>
>
> [image: AMBCB group delay.jpg]
>
>
>
> On Tue, Dec 3, 2019 at 7:55 AM Tom McDermott <tom.n5eg at gmail.com> wrote:
>
>> HI Phil, Attached is the group delay curve for the 40 MHz filter.  It's
>> pretty flat up to about 50 MHz then
>> climbs in the 6M band. The 50 MHz filter has a different shape, but is
>> within +/- 3 nsec through
>> 55 MHz., a lot less delay.   The 50 MHz filter probably doesn't require
>> delay compensation, the 40 MHz does for
>> measurements above about 45 MHz.  8 nsec is one ADC clock sample time.
>>
>> The much bigger concern is the AM broadcast bandstop filter. That has
>> very non-linear phase from about
>> 1.8 MHz downwards. Above 1.8 MHz the delay drops and flattens out. That
>> filter will be much more sensitive
>> to component variation, so it will need to be calibrated on a per-filter
>> basis.
>>
>> -- Tom, N5EG
>> [image: Screenshot from 2019-12-03 07-45-56.png]
>>
>>
>>
>>
>>
>> On Tue, Dec 3, 2019 at 3:29 AM Phil Erickson <phil.erickson at gmail.com>
>> wrote:
>>
>>> Hi all,
>>>
>>>   Sorry that I was not able to join the call last night.
>>>
>>> 1. Receiver: 40 MHz LPF filter is preferred by the group. The loss at 6M
>>>> is a little higher, but likely will need an LNA for 6M use anyway, so that
>>>> may not matter. The nearby-above-61 MHz loss is better with the 40 MHz
>>>> filter. Also include jumpers for power and ground bonding and for use by
>>>> some future low-noise amplifier.
>>>>
>>>
>>>  One point not brought up in this sentence:  the phase response of the
>>> LPF above its cutoff will not necessarily be linear.  Was that discussed?
>>> It might impact any use at 50 MHz, or at the least would require careful
>>> calibration if it were to be used there.
>>>
>>> 73
>>> Phil W1PJE
>>>
>>>
>>>
>>> On Mon, Dec 2, 2019 at 10:11 PM Tom McDermott via TangerineSDR <
>>> tangerinesdr at lists.tapr.org> wrote:
>>>
>>>>
>>>> Notes from PSWS / TangerineSDR call of 12-02-2019
>>>>
>>>> 1. Receiver: 40 MHz LPF filter is preferred by the group. The loss at
>>>> 6M is a little higher, but likely will need an LNA for 6M use anyway, so
>>>> that may not matter. The nearby-above-61 MHz loss is better with the 40 MHz
>>>> filter. Also include jumpers for power and ground bonding and for use by
>>>> some future low-noise amplifier.
>>>>
>>>> 2. Dave W. recommends putting pads for a low cost I2C temperature
>>>> sensor on the magnetometer module just in case the PNI-3000 has temperature
>>>> sensitivity and needs compensation. Scotty recommends adding a strap to one
>>>> of the temperature sensor address lines so that sensors on the local and
>>>> remote ends can be separately addressable.
>>>>
>>>> 3. We currently do not have a logo for the Personal Space Weather
>>>> Station. Would such be useful? Dave L., Scotty, and Nathaniel will add some
>>>> material to the tangerinesdr.com webpage tying the various parts of
>>>> the project together.
>>>>
>>>> -- Tom, N5EG
>>>>
>>>> --
>>>> TangerineSDR mailing list
>>>> TangerineSDR at lists.tapr.org
>>>> http://lists.tapr.org/mailman/listinfo/tangerinesdr_lists.tapr.org
>>>>
>>>
>>>
>>> --
>>> ----
>>> Phil Erickson
>>> phil.erickson at gmail.com
>>>
>>

-- 
----
Phil Erickson
phil.erickson at gmail.com
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