K4JCW Balloon opportunity - measure your station today!

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n6gn's picture
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K4JCW Balloon opportunity - measure your station today!

I'm writing this Saturday July 8, 2017 at 1900 UTC.

Today a K4JCW balloon is right offshore the Miami area and line-of-sight to stations on the Eastern Florida Coast. Winds aloft are taking it mostly northward and it can be expected to go near Fort Lauderdale before it heads out to sea more.
The reason this may be of particular interest is that the balloon represents a stable, known ERP. It is running about +11 dBm into a 2 dBi antenna. Thus it is a 20 mw ERP source, line of sight to stations along the coastline. Because it is at several km elevation, this combination of known 'mobile' ERP and WSPRs S/N reporting makes accurate measurement of a receiving station's antenna efficiency and local noise floor. These are ESSENTIAL parameters for any station, no matter how big or small.

By simply listening and spotting with WSPR the S/N of the balloons signals either when sending the K4JCW ID packet or a "Q" prefixed callsign, using the (then) precisely known location of the transmitter and its ERP, it is a simple matter to calculate station absolute noise floor modified by the antenna gain. For mononopole, dipole or similar "simple" antennas this leads to a good measurement of receiver noise.

Why do you care? Because this noise is very likely the biggest limitation by far to your station's receive ability. Knowing the level of the noise accurately can give you a path to greatly improving your station!

From scouring the WSPR database for May and June of 2017, I find there to be only a very few S/N spots of the beacon above 0 dB. A dipole WITH A LOW NOISE FLOOR should easily produce these kinds of reports from the LOS balloon. If your station does not do this, you very likely have common mode noise current on your receive feedline. This problem, which can raise noise floors terribly, 30 dB or more, can be remedied.

From other studies of the WSPR database, I am coming to the conclusion that a vast majority, but not all, 20m WSPR stations suffer from much higher noise levels than they should.

Perhaps more to come in a future post. For today and maybe the next few days while the balloon is running up the Eastern US coast, take the opportunity to spot the balloon and record a S/N from a WSPR spot. Calculation of noise floor can be done after the fact as long as you are on and listening and getting spots.

This tool is by far most valuable when the balloon is within LOS, probably 200 miles, of the ground station. Once the ionosphere is involved the numbers are much more difficult to interpret.

If you are fortunate enough to be on its route, perhaps within 200 miles of the sub-balloon point, such that you can "see" the balloon, either the K4JCW call or one of the Qx2xxx calls in the +10 to +20 range, you probably have a noise environment that is under control. To the degree that you cannot, you probably have some great improvements possible.

Don't fall for the "digital devices have made the bands too noisy in the last 20 years" common argument/complaint. WHile the generators of our noise may be these devices, there's a good chance that much of this problem is not radiated noise but noise getting to your receiver because of common mode current on your feedline.

Other chances like this may come along with this or similar balloons but again they may not. If you're along the path, get on 20m WSPR and measure the balloon while you have the opportunity!

Glenn n6gn