Hi Don,
I may just break down and buy the DXE product! :) Thanks for sharing
that info.
73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources
On 4/12/21 6:03 PM, Don Kirk wrote:
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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