[RFI] 70cm impulse noise

[Christopher Wawak]

Hi Jim, thanks! Fascinating suggestion! I think one thing that will tell me
a little bit more about the noise is how time/weather affects it. I've only
had the antenna up a week or so.

I have two questions:

1. The noise seems to end at dark - I'm guessing that these aircraft
operate on a schedule that doesn't necessarily stop at sundown. Would that
be a reason to eliminate it as a possibility?
2. The noise gets weaker as I point my antenna to the sky. It's strongest
when elevation is pointed towards horizon, which to me suggests something
close and on the ground, since the antenna itself is at about 6', sitting
on a tripod on my backyard. Am I correct in that, or am I missing something?

Thanks again for replying - I'm sure I can get this figured out, or I'll
feel real silly spending all this money hihi!

73 Chris KC2IEB

On Fri, Aug 13, 2021 at 9:13 AM AA5CT <jwin95 at yahoo.com> wrote:

>
> E2C or the later E2D possibly.
>
> APS-145 uses UHF (including the ham band) for operation. There
> is a newer RADAR on the later E2 series mini-awacs which also
> uses UHF.
>
> I used a pair of yagi antennas and two receivers (in AM mode) some
> years back to 'listen' to their movement in the skies before I figured
> out what I was listening to.
>
> I only offer this as one possibly that I was able to determine
> definitively.
>
> de AA5CT Jim
>
> -----------------------------
>
>
>
>
>
> On Thursday, August 12, 2021, 6:17:16 PM GMT-5, Christopher Wawak <
> kc2ieb at wawak.org> wrote:
>
>
>
>
>
> Hi! During the day, there is often what sounds like lightning noise from
> ~436-440 MHZ. It is an intermittent crackling, strong enough to totally
> make the AGC crank and make it impossible to hear anything on satellites. I
> turned off the power in my house, and disabled all UPSes and saw the same
> noise. Tuning anywhere else in 70cm is fine, no noise further up the band.
> The noise happens whether or not I’m transmitting, whether or not the
> preamps are in line, on or off, and I’ve replaced all the coax!
>
> I just set up a new Satellite ground station consisting of an icom 9700 and
> M2 LEO PACK set of 2m and 70cm circularly polarized antennas. These are
> connected to SSB.de preamps which have the gain adjusted to minimum. On the
> 70cm feedline near the receiver I added two mix 61 ferrite toroids. No
> improvement. Feedline is approx 115’ of LMR400. I have also heard the noise
> on an icom 705 with an arrow vhf / uhf hand held yagi satellite antenna. I
> drove around the neighborhood and couldn’t get a good bead on where it may
> be coming from other than “west”. It’s too hot to go on foot right now.
>
> I’ve heard it since last weekend, and it’s been present most days, but
> increases and decreases in the frequency of pops. I am keeping a log.
>
> Here is a .wav recording from today:
>
>
> https://drive.google.com/file/d/1Jl6wB-hJOpY0SDroQQQHw2uMUFdFwiF7/view?usp=sharing
>
> Here is the waterfall, the horizontal wide lines are  are impulse noise I
> hear. No audio, but maybe useful.
>
> https://www.youtube.com/watch?v=tbEWNWZnf1o
>
> I have trouble direction finding this type of noise - it seems to come from
> everywhere! Does it make sense to add more ferrites? I don’t think this is
> common mode but…
>
> Thank you
>
> Chris KC2IEB
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