Research  Articles

Clean Power Supply

Examining the voltage accuracy of DC power supplies.

FSQ with Fldigi

How to set up Fldigi for FSQ operation.

Great Circle Route

Proper determination of beam heading.

Image Quality

Calculating SSTV image quality.

Measuring Mighty Fine Junk

Evaluating the accuracy of MFJ's attenuator.

RX Frequency Calibration

Evaluating the accuracy of ham receiver frequency calibration.

Seeking SNR

An exploration of techniques to improve SNR, hence Rx effectiveness.

Sky Noise

How noise power is determined from sky Temperature, bandwidth and the Boltzman constant.

S-Meters

A study of gross inaccuracies with ham receiver S-meters.

SSTV Transmission Methodolody

Description of how an SSTV signal is encoded for transmission.

Soldering PL-259 Plugs to Coax

An effective way to solder.

Wolf River Dipole Effectiveness

A comparative study for a prototype Wolf River rotatable 40 meter dipole.


Wordsworth  CW

Play / Pause
#1 Common digraphs Part 1 (last: ea)

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#2 Common digraphs Part 2 (co)

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#3 Common trigraphs (sth)

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#4 Common double letters (zz)

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#5 Wordsworth 2 characters Part 1 (gm)




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#6 Wordsworth 2 characters Part 2 (b4)

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#7 Wordsworth 3 characters Part 1 (rpt)

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#8 Wordsworth 3 characters Part 2 (yrs)

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#9 Wordsworth 3 characters Part 3 (are)

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#10 Wordsworth 4 characters Part 1 (just)




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#11 Wordsworth 4 characters Part 2 (tcvr)

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#12 Frequency used words, study 1 (been)

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#13 Frequency used words, study 2 (summit)

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#14 Frequency used words, study 3 (great)

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#15 Frequency used words, study 4 (into)




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#16 Frequency used words, study 5 (off)

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#17 Frequency used words, study 6 (said)

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#18 Frequency used words, study 5 (upon)

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#19 Frequency used words, study 6 (your)




ImageMagick Picture Quality

The quality of a received Slow Scan TV (SSTV) picture may be determined by comparing, pixel-by-pixel, for identical matches in RGB color space for the customary image displayed on an SSTV cam in JPG format. If a ham received an image perfectly, there would be a 100% match. However, with analog transmissions, this will never happen. Considerable image degradation occurs as soon as the software, eg, MMSSTV, readies the image for transmission and losses are magnified as the signal encounters path loss when it moves through the ionosphere.

ImageMagick is powerful software package that can compare two images pixel-by-pixel, e.g., a 320x256 pixel JPG image from an SSTV transmission. This is a total of 81,920 pixels in many SSTV pictures. The ratio of matches to the total is expressed as a percentage. This may be viewed as a measure of picture quality received.

In practice there is significant deteriation. A 'fuzz' adjustment is available in ImageMagick. Fuzz is used to match colors which are close to the target colors in RGB space. Colors within this distance are considered equal. Fuzz may be expressed in absolute intensity units, or as we will do for SSTV image comparisons, expressed as a percentage of maximum possible intensity value of each pixel.

From experimentation, 10% might be a useful fuzz tolerance level for expressing the quality of a received image.

Upload 'original' image to be used as the standard of comparison.

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Upload one or more images, most likely degraded, for a quality percentage comparison to the original.

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Ham  Hunting

I developed this web functionality after a QSO with Dutch KYØR in Pueblo, CO. Soon after our QSO a rogue operator came on frequency spouting vile profanities and failing to ID: all illegal operations.

That gave us the idea of triangulating to generally locate the signal. I had a general idea, but on the spot, we did not succeed in finding his general area of transmission.

This section is designed to rapidly gather the necessary information to suggest an approximate lat/long for the violator, and to display visually on a map.

This preliminary information would be helpful to an Official Observer (OO) in that region who might with the help of more local hams start to pinpoint the offender, and ultimately involve the FCC in discovery.

Step #1 is to determine the lat/long of two ham radio stations which will serve as initial observers. Simply insert the call sign. You will the obtain the signed decimal degrees, where negative indicates west/south. My QTH is inserted in the first row of the subsequent table.

Enter any call sign:
    


Step #2 is to insert the lat/long for station B, and then each station should find the best beam heading to indicate maximum strength of the offending signal and insert in the table (180 is defaulted).

WA9TT: , Bearing WA9TT:
Ham Station B: , Bearing Station B:

Intersection point:

 


Now for Step #3, copy the resulting longitude, latititude Intersection Point data into the Latitude & Longitude boxes below, and then click on "Search." Be sure to separate the degrees, minutes and seconds by spaces, and lead each appropriately with an "N" or "W" as in the example with my QTH inserted.

Latitude Longitude
Satellite Picture


Step #4: Once the general area of the country is found, you may wish to look for local hams who might be able to help take the investigation a step further. You can do so via Reverse Call Sign Look-up from the US FCC data base.


Technical notes: The geometric formulas are calculated on the basis of a spherical earth, ignoring ellipsoidal effects. This is accurate enough for first approximation of a distant ham station. The earth is very slightly ellipsoidal. Using a spherical model gives errors typically up to 0.3%.