[time-nuts] Spectrum Analyzer Specifications
Bob Stewart
bob at evoria.net
Fri Mar 25 02:05:46 UTC 2016
Hi Bob,
Could you use a gate instead of an amp?
Bob
--------------------------------------------
On Thu, 3/24/16, Bob Camp <kb8tq at n1k.org> wrote:
Subject: Re: [time-nuts] Spectrum Analyzer Specifications
To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
Date: Thursday, March 24, 2016, 5:48 PM
Hi
That’s another good point about the need to
work out a target device. Both
of the
possible target devices I mentioned have enough channels to
do at least a
dual channel measurement.
That would add another mixer and a pair of power
splitters along with another amp chain.
The other part of that news is
the RF drive power required goes up. You can do a pretty
good job
of saturating an RPD-1 with +7 dbm.
Most (but not all) OCXO’s and other gizmos will
provide that without any amplifiers involved.
Adding a 3 db splitter gets you into the 10 dbm
range. That is getting fairly close to the
limit for a lot of devices.
You can add an amp. The ones that work without
impacting the phase noise of a high quality
OCXO cost as much as the audio cards or USB
devices. Cost wise, I’d keep that sort
of
thing off the main board.
So what is the second channel worth?
The basic single channel
design will get you into the -173 to -176 dbc / Hz range on
a fairly high
power pair of OCXO’s. The
cross correlation “stuff” will get you past that point.
Is that worth taking
the BOM (without board
and power supply) up to $80 or so? Consider that with the
board and
power supply, it likely is over
$100.
Would I do it as an
accessory to a Janus or QA401? Maybe. You would need to pick
one or
the other. In the case of the Janus,
there are more software issues and some noise floor testing.
The QA401 is mighty expensive. The original
idea was to use the sound card you already have ….
Bob
> On Mar 24, 2016, at 5:30
PM, Bruce Griffiths <bruce.griffiths at xtra.co.nz>
wrote:
>
> If the
software implements acquisition of cross power spectra
> Then one could implement a near state of
the art cross correlation PN test set
>
based on this.
> With a suitable preamp
the sound card could also be used for power supply and
> reference noise measurement.
>
> Bruce
>
> On Thursday, March
24, 2016 04:54:47 PM Bob Camp wrote:
>> Hi
>>
>> The board is pretty non-critical.
It’s 90% audio. The biggest hassle is a
>> power supply. You would *like* a
fairly high voltage, at least if you are
>> driving a spectrum analyzer. That may
not be quite the case with a sound
>>
card. It depends a *lot* which one you are running.
Something like a QA401:
>>
>> https://www.quantasylum.com/content/Products/QA401.aspx
>>
>> Would make a
good target device. It’s based on the AKM 5397 So might
some
>> Janus boards. They are based
on the earlier(?) AKM 5394. The QA401 has the
>> advantage of a nice box and full USB
isolation (ground loops are a pain).
>> It also has drivers and all the OS
hooks. The Janus is a bit more “DIY”
>> with no drivers or interface (let
alone isolation). The Janus is < 1/4 the
>> price.
>>
>> The high voltage (+/- 18V linear
regulated) supply approach makes a lot of
>> sense with the QA401. It probably does
not make as much sense with the
>>
Janus. Switching regulators of any sort are something I
would strongly
>> recommend against in
a system like this that is trying to measure noise
>> floor at audio ….
>>
>> The
schematic changes a bit depending on what the target is. I
can draw it
>> up if there is a
consensus on the target. One example: If the “sound
card”
>> is DC coupled, you can use
it to indicate (and check) quadrature. If it’s
>> an AC device, you need some sort of
isolated output for another indicator.
>>
>> Bob
>>
>>> On Mar
24, 2016, at 1:31 PM, John Ackermann N8UR <jra at febo.com>
wrote:
>>>
>>> I'd be willing to assist with
board layout if someone wanted to make this
>>> into a real project (e.g., fully
developed schematic). TAPR might be
>>> talked into supplying at least
bare boards; we'd have to get a sense of
>>> demand before committing to a full
kit or assembled unit.
>>>
>>> John
>>>
----
>>>
>>> On 3/24/2016 9:04 AM, jimlux
wrote:
>>>> More like $40 in
parts, without a board, etc.
>>>> The RPD-1 is $20.70
>>>> LT1678/LT1679 is a nice low
noise opamp that does rail to rail and is
>>>> about $5
>>>> etc
>>>>
>>>> On 3/24/16 4:42 AM, Bob Camp
wrote:
>>>>> Hi
>>>>>
>>>>> Pretty simple:
>>>>>
>>>>> Double balanced mixer,
RPD-1 is one option, there are others.
>>>>>
>>>>> Fairly simple L/C lowpass
between the mixer and an op-amp.
>>>>>
>>>>> 20 db positive
(non-inverting) op-amp amplifier string after the mixer
>>>>>
>>>>> Output of the string goes
to the sound card. Use a good (dual / quad)
>>>>> audio op amp
>>>>>
>>>>> Quadrature amp picks off
the output of the first op amp stage, switch
>>>>> and resistors to set gain,
pot to set op point.
>>>>>
>>>>> ====
>>>>>
>>>>> So what you have is an old
style quadrature phase noise amp and “PLL”.
>>>>> More or less a very junior
version
>>>>> of the 3048
test box. Like any setup of this sort, you check two
>>>>> similar oscillators. They
run in quadrature and
>>>>>
you do a few “measure this with switch in position A”
sort of things
>>>>> to set
things up each time.
>>>>>
>>>>> Nothing exotic.
>>>>>
>>>>> Bob
>>>>>
>>>>>> Any documentation on
this $40 phase noise test set?
>>>>>>
>>>>>> Rick N6RK
>>>>
>>>>
_______________________________________________
>>>> time-nuts mailing list -- time-nuts at febo.com
>>>> To unsubscribe, go to
>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>> and follow the instructions
there.
>>>
>>>
_______________________________________________
>>> time-nuts mailing list -- time-nuts at febo.com
>>> To unsubscribe, go to
>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the
>>> instructions
there.
>>
>>
_______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the
>> instructions
there.
>
>
_______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts at febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
More information about the Time-nuts_lists.febo.com
mailing list