Greetings all from the UK
I read the following post with interest about a shortwave transmitter
http://www.part15.us/forum/part15-forums/transmitter-talk/ism-shortwave-transmitter-continued
My question is what kind of range have users in the USA managed to get?
I too can use this transmitter in the UK but ofcom state that the power output should be no more than
42 dBμA/m at 10 m
Could this number be converted to a mW power limit and if so what would that roughly be?
Or is there an estimate of range that a signal of 42 dBμA/m at 10 m would give?
Any insight would be greatly appreciated
Cheers
Below is a partial quote from http://www.erodocdb.dk/docs/doc98/official/pdf/Rep074.pdf (the result of a Google search).
"IDENTIFICATION SERVICES AND THE RADIOASTRONOMY SERVICE AT 13 MHz
The band 13.553-13.567 MHz is designated by the ERC recommendation CEPT/ERC/REC 70-03 for non specific Short Range Device (Annex 1) and Inductive Applications (Annex 9). The fieldstrength level is 42dBμA/m at 10 m, equivalent to approximately 10 mW ERP."
ERP = Effective Radiated Power
A center-fed, 1/2-wave, linear dipole antenna in free space can produce an ERP of 10 mW in the directions perpendicular to its longitudinal axis when about 6.1 mW of transmitter power flows into its input terminals.
However reflections of the radiation from that antenna or any other antenna mounted near the earth might produce net fields at 10 meters that could exceed the permitted field when using 6.1 mW of applied power, and even less power than that.
I would not recommend this particular device.
It took 3 tries for the vendor to get it right (i.e., getting rid of the distortion). And some never got it right.
I'm not convinced that its output was anywhere near 10 mw (it was supposed to be 100). Range was exceedingly poor, even using my continuously tuned amateur radio vertical (a few hundred feet).
I gave up shortly after that, and it sits somewhere in a box, gathering dust.
"Or is there an estimate of range that a signal of 42 dBμA/m at 10 m would give?"
Forgot to respond to that part of the post.
Using vertical polarization, radiating 10 mW in the horizontal plane on 13.56 MHz produces a groundwave field of about 60 µV/m at a distance of 1 km, over earth having 5 mS/m conductivity (about average).
what is the average field strength required for good noise free reception at those frequencies? 60uVm at 1km for 88-108mhz or 525-1700khz is real good but maybe not so good for 13 mhz? i think here in USA we are only allowed less than 1mW ERP on those frequencies.
@Rich - Thanks for that,I too thought it would be 10 mW
@Artisan Radio - Thats a shame,the ebay SW transmitter is so poor.I havent found any others for sale.
I would build my own but am not technically able yet!
Thanks again