[amsat-bb] QRP re deux
jdanehy at cinci.rr.com
Fri Dec 19 15:49:30 PST 2008
Jack KD1PE et al
A ham radio antenna installation is not very static (no pun intended) it is rather dynamic ; to wit : improper assembly of a antenna (variation from the instruction), age and mounting losses of the coax from ultra violet rays, water intrusion, the angle of the antenna wave vs. where the satellite is at the moment, use of improper coax connectors, i will keep the list brief . . .
to repeat it is a dynamic (constantly changing ) situation not a static (stay put) system . . . when a TV or FM station states its ERP it can do so with more certainty since it uses very sophisticated instrumentation and hardware that is relatively static ( coax with helium etc) . . . commercial antennas that have rigorous specifications installed by professionals etc . . . so for a ham radio QRP set up you can make a SWAG (simple wild a_ _ guess) . . .
a db loss from ultra violet, another for water intrusion and still more for bad connectors and you have 2 or 3 db (loss of half your imagined ERP) then find out like I did that M Square sent me elements that did not pass QC (quality control) and I got a simple ; " ah shucks" from my telephone call and confirmation by others on this BB (bulletin board) that indeed they too had received elements that did not conform to spec . . . a hack saw fixed that goof
Add to that the db or two loss from the guy in New York State (some university) that told me that he just assembled his M Square antenna by starting with the longest element and progressively assembling the shorter ones to the boom DESPITE admonishment from M Square that there would be 1 or 2 sequences when the progression would require a longer element ( probably to reduce side lobes ) . . OK : so many feet of LMR 400 or RG 213 and what did the manufacture say about db gain ? do the math calculating the feed line loss and multiply that by the gain = simple QRP power . . . OK well what is the mfg's gain . . . advertised , isotropic, vs a dipole . . . read the fine print . . . not many do or even know the difference. . .what if any gain to you give a 1/4 wave ground plane ? ? ? where is its major lobe when the satellite is at 70 degrees of elevation . . . OK let me change my QRP calculation after checking the printout of the ground plane's loss . . .
the premise that I follow is that QRP in the ham fraternity for decades prior to AMSAT was 5 watts output from the final stage of the transmitter . . . any other attempt which hopes to replicate that simplistic approach is speculation based upon a dynamic that is flawed from lack of accurate measurements . . . and constantly changing parameters . .
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