It's all about the Software

Hello,

A very general sort of question.

Have often what I can call a "bouncing baseline," generally over most anywhere in the spectrum.

Perhaps +/- 2.5 dBm. Sometime more. Sometimes very steady, but usually not.

What are the possible causes for some effect like this ? Normal ?

Too much gain perhaps ? Just the vertical scale I am using to look at the Spectrum ? Or,...?

Thanks,
Bob

How close to an AM BC station are you? Use the following and look for AM stations only:
https://radio-locator.com/cgi-bin/locate

73 Kriss KA1GJU

Static crashes?

I believe Robert11 lives 30m south of me, just west of Boston. Very close to a field of +1000' towers for TV, and radio.
160M has been great for past several days, no thunderstorms anywhere!
My noise floor pulses, but it's due to picking up an electric fences from 3 different farms from .5 mile to .9 miles away.
You can see 3 separate pulses, at 1 sec intervals, local sunrise was one hour ago:

73 Kriss KA1GJU

Hi Kriss,

Ran your link to the find local stations, and was I ever surprised.
Guess there are 14 in area, and some quite close and strong. Not just the Boston ones.

I guess it would not be appropriate to attach a screen shot here, but if you bang in 01776 you can see what I mean.

So, interference from them is apparently a good bet.

As always, thanks for thoughts and help.
Stay well,
Bob

Bob,
Set the visible bandwidth up so you can see the strong stations, but also see some dead space between. Then sit back from screen and see which strong signal is pulsing the noise floor in sync. Rather easy to do when the offending station is talk radio, due to the voice peaks. You might be able to find the offender by tuning 2X or 3X the AM band. My guess would be WRKO on AM 680. So 2X that would be 1360 kHz (Still inside the AM BC band), but 3X would be 2040 kHz (just above the 160M band of 1800-2000kHz). As I recall from previous emails, you are running an SDR Play of some version. With good antennas, they are easily overloaded with nearby AM BC signals. I only have one in my fleet of SDR's (thanks to a lightning hit!), but I HAVE to have an AM BC filter in front of it. The built in AM BC filter, selectable by SDRC, works somewhat. I built the W1VLF filter and it's on that server, Super Station #2, as noted in the Server notes. So AM DX'ing is really not recommended on that server since the filter knocks down the AM Band by about 30dBm.

OK, here's a test with two instances of SDRC running. Both are AirSpy units, with the exact same gain settings. The left-hand image has no AM BC filter, the right has the W1VLF home brew filter. Note the yellow box under the S-Meter, one is at -29.2 and the other at -50.5. Using 'new math' aka 'public math', that's a 29.3dBm difference! Somewhere, I have before and after images of the SDRPlay that is using the AM BC filter. It too was just dramatic as the image below.
AM BC filters are available off the shelf, or you can build your own with a handful of parts. I have enough to build a few more somewhere in my shop... I think.
One just has to be aware of the frequencies being blocked, I like to listen to 160M, just above the AM band, so Super Station #2 with the filter inline on ALL the RXR's in that installation, has some attenuation since the filter doesn't magically stop at 1700 kHz. It's effectiveness slowly tapers off as you progress upwards in frequency through the 160M band.

73 Kriss KA1GJU

Hi Kriss,

Will definitely try your experiments, and will let you know.

Interesting subject to learn more about.
Have never really considered local interference much; certainly should have.

Bob

Hi,

No explanation that I have any confidence in, but Baselines in the Spectrum view seem solid lately.
Problems that are intermittent in nature always drive me crazy.

There is a Ham about a block from me, and he has a Very tall tower in the backyard.
Don't know him, so can't get any details on what he exactly does, but...

Perhaps his transmissions were/are the cause of my baseline jumping around ?

Anyway, it it returns, will try your suggestions, and let you know.

Thanks again for help,
Bob

Bob,
It's very easy to find him on the bands with an SDR. If your SDR is on the same band while that station is in operation, you will see
a swath of signal across your spectrum and waterfall display. Using the attenuator, you can zero in on the exact frequency.
Bands to start looking at are:
20M - 14.00 to 14.350MHz Day and into early night
Maybe 17M if daytime 18.068 to 18.168MHz
40M - 7.00 to 7.300 MHz Day or night
80M - 3.50 to 4.00 MHz Day or night
If you were to tune a random frequency in those bands and see massive overload, you will have found the problem!

Here's a band plan chart to look at: https://www.icomamerica.com/en/amateur/amateurtools/US-BandPlan-Update-1-2020.pdf

The upper bands, 15M & 10M are open sporadically, or if a contest is going on (usually Friday night to Sunday night) there will be some activity if the nearby ham is a contester. The 12M and 17M bands are WARC bands, so there are no contests up on those. In fact, 17M was really busy this AM with European stations booming in!

73 Kriss KA1GJU