For antenna measurements with a spectrum analyzer, if you have a fairly
efficient receiving antenna, the preamp will typically overload, and in
addition you may have to add attenuation. I suspect that anything
described as "tiny" does not have a high dynamic range preamp. If you
connect a short whip as an antenna, the noise from the preamp will
dominate and you not be able to hear over the air noise. Any ham type
radio receiver will run circles around a spectrum analyzer for the
purpose of this test. We all own one or more of those; why not use
them? An SA is simply the wrong tool.
---
Rick Karlquist
N6RK
On 2025-07-08 15:57, David Eckhardt wrote:
> QUOTE (John, K5QX):
> In general, most SA's have a very high noise figure. And a built in
> whip is an inefficient antenna on 40 meters. So this "measurement" is
> probably fairly meaningless.
> ***********************************************************************
>
> Hold on there. Yes, in the "old days" and even the HP 8566 and 8568, the
> input noise figure was in the vicinity of 18 to 23 dB. In those days a
> preamp was usually used for measurements to bring the noise figure down to
> around 3 to 5 dB (5 dB is a typical run-of-the-mill modern HF receiver).
>
> _However_, these days, the vast majority of spectrum analyzers offer an
> internal preamp. This includes the TinySAs from Eric. Therefore,
> measurements made with the small telescoping antenna are pretty good.
> Absolute levels are not good, but relative measurements can be quite
> accurate. In addition, an antenna which is at or less than 0.05 (5%) of a
> wavelength is an excellent tool as its response does not "color" what is
> being measured.
>
> Dave - WØLEV
>
> On Tue, Jul 8, 2025 at 8:27 PM Richard Karlquist <richard@karlquist.com>
> wrote:
>
>> In general, most SA's have a very high noise figure. And a built in
>> whip is an inefficient antenna on 40 meters. So this "measurement" is
>> probably fairly meaningless. To get a meaningful measurement, you need
>> a combination of an antenna and a receiver that is sensitive enough to
>> hear noise off the air. For the antenna, I like to use a tuned loop
>> antenna. For a receiver ... well a real "communications receiver" (not
>> an entertainment device) with a noise figure below 10 dB. (turn on the
>> built in preamp). I like to use an Icom 706 running off a gel cell.
>> The off the air noise should peak as you tune the loop. (Do not use an
>> untuned loop with a preamp; you will only hear preamp noise, not off the
>> air noise).
>>
>> ---
>> Rick Karlquist
>> N6RK
>>
>> On 2025-07-08 10:13, John Warren wrote:
>>
>>> Has anyone in Texas installed whole house backup batteries from Base Power
>>> in Austin, Texas? I am considering installing their batteries and am
>>> looking for any insight on potentional RFI issues. My neighbors have their
>>> batteries installed and they were kind enough to allow me to take some
>>> rough measurements.
>>>
>>> I used a TinySA spectrum analyzer with the built-in telescoping antenna and
>>> did find that at the inverter enclosure for each battery there was around a
>>> 10 dB increase in noise from around 7 to 10 MHz and another similar peak in
>>> the area of 14 MHz. The noise level dropped quickly as I moved away,
>>> disappearing completely around 3 to 4 feet from the inverter enclosure.
>>> Around the other sides of the battery and conduit that connected to the
>>> house, there was no excessive noise.
>>>
>>> I plan on going back over with a portable AM/FM/SW radio and the TinySA
>>> again to make some better measurements and document what I find.
>>>
>>> Thanks for any input anyone may have.
>>>
>>> 73,
>>>
>>> John K5QX
>>> _______________________________________________
>>> RFI mailing list
>>> RFI@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/rfi
>> _______________________________________________
>> RFI mailing list
>> RFI@contesting.com
>> http://lists.contesting.com/mailman/listinfo/rfi
>
> --
>
> Dave - WØLEV
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