```I share the same concerns as Jim. For instance to be realistic the 500 khz equipment and antenna would need to be operational for such a test and that is not possible without the SRP Theoritical measurements would be meaningless and often differ from practical field tests. I think this RFI assessment area needs clarification from Ofcom. de Mal/G3KEV ----- Original Message ----- From: "james moritz" <[email protected]> To: <[email protected]> Sent: Thursday, February 22, 2007 12:18 PM Subject: RE: LF: Special Research Permits (501-504kHz) for UK Amateurs Dear Dave, LF Group, I don't believe it is possible to give an accurate value for field strength at points close to the antenna - it will depend on too many variable factors, such as the position, geometry, conductivity and dielectric properties of all nearby objects. One can come up with a reasonable sort of "worst-case" figure, however; this is my attempt: -Assume a long-wire antenna with an effective height of 8m. With lambda = 596m, radiation resistance Rrad will be 0.285ohms. -To achieve 0.1W ERP, Iant = sqrt(Perp/1.8xRrad) = 0.44A (I am assuming directional gain of 2.6dB, i.e. 1.8 for a short vertical antenna over a dipole) -The antenna voltage depends on the current and the impedance of the antenna. Most of the impedance is due to the capacitive reactance of the antenna. The measured antenna capacitance is about 340pF, giving a reactance of 931ohms at 503kHz. Therefore the antenna voltage will be about 411V. (Also, the loss resistance of this antenna at 500kHz is around 20ohms; the TX power required to obtain 0.44A therefore works out to be about 4W) -If as a worst case we assume the antenna and ground acts as a sort of parallel plate capacitor with the physical height of 9m being the spacing between the two plates, the E field strength will be about 46V/m under the antenna. In reality, the field gradient will be higher close to the antenna wire than it is at ground level, so the field strength will be lower than this at ground level. Also, at positions not directly under the antenna the field will be further reduced, and trees, buildings, bushes, cats etc. in the vicinity will have a partial screening effect that will also reduce the field strength. So I think 46V/m is a very conservative maximum figure for this antenna. A bigger antenna will have lower reactance, require less current due to higher Rrad, and be further away from potential "victims", so would result in lower FS. The converse applies to small antennas. As you can see, the above figures are pretty tiddly compared to what we are used to at 136k, or at HF for that matter. At my QTH, the FS due to the nearby broadcast transmitters is around 20V/m. Does anyone know offhand what Ofcom might regard as an unacceptable field strength? I guess one reason Ofcom might be nervous about permitting higher ERPs is the possible effect on MF broadcast receivers with both RF and IF frequencies fairly close to the band. But this does not seem to be a huge problem with 160m, or MF beacons. Another possibility might be the Navtex marine safety broadcasts on 490 and 518kHz, whose receivers might get swamped - but I would think the likelihood of this would be pretty low also. BTW - what are the correct emission codes for modes like PSK31 or Wolf, and FSK / mFSK signals like DFCW and Jason? Cheers, Jim Moritz 73 de M0BMU -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Dave G3WCB Sent: 21 February 2007 17:14 To: [email protected] Cc: John W Gould Subject: RE: LF: Special Research Permits (501-504kHz) for UK Amateurs The first UK applicant to get a 500kHz SRP has to buy the beers. (Won't be me...I haven't yet figured out how to measure the field strength inside my neighbour's siting-room, will it interfere with his toaster, etc) 73, Dave G3WCB IO91RM -----Original Message----- From: [email protected] [mailto:[email protected]]On Behalf Of [email protected] Sent: 21 February 2007 13:17 To: [email protected]; [email protected] Cc: John W Gould Subject: Re: LF: Special Research Permits (501-504kHz) for UK Amateurs Hi John and the list, Congratulations on your new experimental allocation! I see that Ofcom is restricting your experiment to very low power levels: "In general, considerably lower e.r.p. levels than that permitted in the 136 kHz band are likely to be favourable and this will only be permitted where it can be demonstrated that increased powers are necessary for research. On no account will an e.r.p. level of greater than - 10 dBW be permitted under any circumstance." This will pretty much preclude transatlantic work, except possibly for QRS, which is a pity. I wonder what it is that Ofcom is worried about interfering with? The U.S. experimental stations are limited to 20 watts erp, which is 23dB more than Ofcom is allow U.K. amateurs. -- 73 Warren K2ORS/WD2XGJ/WD2XSH/23 FN42hi http://www.w4dex.com/wd2xgj.htm -------------- Original message ---------------------- From: "John W Gould" <[email protected]> > Ofcom has announced today that a limited number of SRPs will me made > available for 12 months from 1st March. See > > http://www.ofcom.org.uk/radiocomms/ifi/licensing/classes/amateur/Notices/200 > 70221 > > and the RSGB and Spectrum Forum websites. > > 73 John, G3WKL > RSGB HF Manager > > > ```