Hi Lee,
I've gotten a little lost in this thread, but if you intend to use the
tinySA with the Portable Flag I would like to comment about the placement
of the attenuators relative to a preamp. I was involved with the initial
field testing of the DX Engineering preamp designed for use with my
portable flag and the first thing I recognized was that having attenuation
before the preamp really destroyed the signal to noise ratio because the
signal is so low from the portable flag and attenuating it causes the
preamp noise figure to become a more dominate factor that degrades the
signal to noise ratio. The design was then changed so that the attenuators
come after the preamp which fixed the problem by keeping the signal from
the portable flag going into the preamp as high as possible. The beauty of
the DX Engineering preamp is that it can be turned off if not needed, and
the attenuators can be used with the preamp on or off which provides a lot
of flexibility to handle all situations, and it also has a selectable high
pass filter to block the AM broadcast band as needed.
Just some things to consider when home brewing your own system if you plan
to use it with the portable flag that has very negative gain.
Just FYI,
Don (wd8dsb)
On Mon, Apr 12, 2021 at 8:33 PM Lee STRAHAN <k7tjr@msn.com> wrote:
> Hi LEV Dave and the group,
> Indeed your comment most true. I have decided that a preamp would be
> the answer for me but to have the attenuator I mentioned in front of the
> Preamp. If I have large signals making IMD I certainly wont need the extra
> gain and dynamic range so attenuate it. If the signals are small they will
> not overload the dynamic range and make IMD generally and the attenuator
> can be off. . The attenuator in the Tiny SA is a menu item a bit unhandy to
> reach in the field. And not much dB range.
> This way the preamp wont have to be a power hog for high level signals.
> With the tiny SA at about -100 dBm noise floor I am thinking adding a 1 to
> 2 dB noise figure preamp which will increase the sensitivity without much
> added noise over the common 18 to 22 dB you mention. Normally in a lab
> analyzer you can adjust the sweep speed as well as the resolution bandwidth
> to get a lower noise display. That’s not an option in the tiny SA. So, I
> will see how this works.
> Any way appreciate the comment as it definitely deserves some thought. .
> Lee K7TJR OR
> From: David Eckhardt <davearea51a@gmail.com>
> Sent: Monday, April 12, 2021 4:49 PM
> To: Lee STRAHAN <k7tjr@msn.com>
> Cc: Dave Cole <dave@nk7z.net>; rfi@contesting.com
> Subject: Re: [RFI] Flag Pennant loop - Tiny SA use
>
> Don't forget the average 'lab' SA has a typical noise figure around 18 to
> 22 dB. All need a preamp for reasonable sensitivity. Many of the lab
> instruments today are being marketed with a built-in preamp for this
> reason. Also, note the dynamic range is degraded by the gain of the
> preamp. It's generally best to have it present but easily bypassable for
> that reason.
>
> Dave - WØLEV
>
> On Mon, Apr 12, 2021 at 8:35 PM Lee STRAHAN <k7tjr@msn.com<mailto:
> k7tjr@msn.com>> wrote:
> Hi Dave and group,
> I find the Tiny SA a little low on sensitivity so I am planning on
> adding an external 20 dB preamp with an easier to use step attenuator for
> RFI hunting.
> I have some other obligations at the moment so I am temporarily using an
> SI 4732 radio which is also a tiny box with AM.
> I have the local power company and a wood products manufacturing company
> working with me on an interesting conducted interference case I will
> eventually report on here later after more tests.
> Lee K7TJR OR
>
> -----Original Message-----
> From: RFI <rfi-bounces+k7tjr=msn.com@contesting.com<mailto:
> msn.com@contesting.com>> On Behalf Of Dave Cole
> Sent: Monday, April 12, 2021 1:00 PM
> To: rfi@contesting.com<mailto:rfi@contesting.com>
> Subject: Re: [RFI] Flag Pennant loop - added benefit of being broadband
>
> BTW:
>
> I am currently working on setting up a tinySA on the FLAG... Try it, it
> is really portable. The tinySA will mount right on the support pole for
> the FLAG. No computer, no SDR, just a box the size of a pack of smokes...
>
> 73, and thanks,
> Dave (NK7Z)
> https://www.nk7z.net
> ARRL Volunteer Examiner
> ARRL Technical Specialist, RFI
> ARRL Asst. Director, NW Division, Technical Resources
>
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>
>
> --
> Dave - WØLEV
> Just Let Darwin Work
>
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