[RFI] Flag Pennant loop - Tiny SA use

Mon Apr 12 21:14:50 EDT 2021

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 at 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 at gmail.com>
>> Sent: Monday, April 12, 2021 4:49 PM
>> To: Lee STRAHAN <k7tjr at msn.com>
>> Cc: Dave Cole <dave at nk7z.net>; rfi at 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 at msn.com<mailto:
>> k7tjr at 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 at contesting.com<mailto:
>> msn.com at contesting.com>> On Behalf Of Dave Cole
>> Sent: Monday, April 12, 2021 1:00 PM
>> To: rfi at contesting.com<mailto:rfi at 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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