I'm coming into this discussion at mid-point, so making my apologies:
QRP as a term originated with low power ham stations on HF where antenna gain is usually not that much. Mostly HF QRPers are using dipole or other wire antennas having little gain. The definition of HF QRP is <5w CW.
ON VHF (and satellites) antenna gain is easier to obtain due to the smaller wavelength, so really one should combine transmitter power with antenna gain to determine total RF power (technically, this is called ERP). If you have a significant length of coax cable (loss) that should also be factored in.
You can do it two ways: convert everything into watts and ratios or everything into dBw and dB's. I would say the convention for satellite QRP has become 5w and less than 6-dB: that results in 5 x 4 = 20w ERP or 7dBw + 6 dB = 13 dBw.
You may disagree with using 5w or the 6 dB gain figure, but QRP should not be very high ERP in any case. BTW the 3-element Arrow has about 6-dB gain.
For instance one would not consider 5w into a 16-foot dish on 1268 MHz as QRP: The dish gain is ~ 32 dB or a ratio of approx 1585:1, so: 5 x 1585 = 7.9 kW ERP 7 dBw + 32 = 39 dBw
Note: that I have used gain over a dipole in these examples, whereas normally space communication formula use dBi (isotropic gain). 1 dBd = 2.15 dBi
Info that is probably useless: My four 2m eme yagis provide 19.2 dBd and I run about 125w at the antenna terminals thus my ERP= 10.4 kW For eme this IS considered QRP since the norm is an ERP of 100 kW for Moonbounce.
Perhaps it is better for satellite controllers to indicate what the maximum in power and antenna gain a station should use for uplink, then no one is required to know how to calculate ERP.
73, Ed - KL7UW
At 08:22 AM 12/18/2008, Jim Danehy wrote:
QRP folks do not ESTIMATE . . . . go to a VHF UHF convention and watch the antenna measurements . . . . of course you can SPECULATE or GUESS but that is the ambiguity that is introduced . . . a more accurate means of measuring QRP is the measurement of output power that has been in use by the amateur community for the six decades I have been around . . . antenna gain measurement is not simple . . . it is the execution of the assembly and construction ( the devil is in the details ) of an antenna . . . keep the guess work out of it . . . there was an advertisement some years ago for the ALPHA Amps . . . "life is too short for QRP" . . . if the goal is to set aside a frequency or repeater for challenged signals (compromised antennas and low power rigs ) that is fine . . . express it in the terms you want to convey . . . . QRP for most of the amateur community is measuring 5 watts output at the rig . . .if you want : tell them HT use only with Arrow, Elk, eggbeater and vertical antennas . . . . then you will effectively communicate your goal . . if that is your goal . . . . QRP is not a relevant term if you want to have a place for HTs with small compromised antennas . . . folks get lazy and use short cuts . . . unfortunately . . . .
Jim W9VNE
----- Original Message ----- From: "Nigel Gunn G8IFF/W8IFF" [email protected] To: "Jim Danehy" [email protected] Cc: [email protected] Sent: Thursday, December 18, 2008 12:04 PM Subject: Re: [amsat-bb] what is QRP
QRP is not generally based on ERP. It's usually taken to be 10W PEP SSB or 5W carrier power max for other modes.
I think QRP on sats used to be considered to be less than 10W ERP. It's not difficult to estimate feeder loss and antenna gain.
Jim Danehy wrote:
QRP is a measure of the transmitter output . . . on a practical basis how would an operator accurately measure the ERP if you were using ERP (effective radiated power) as a QRP benchmark . . . you would need instrumentation to measure the feedline losses and sophisticated instrumentation to measure the gain of an antenna . . . most of that type of instrumentation is beyond the average amateur radio operator . . . . but most do have access or use of a watt meter . . . . thus the simple way of calculating QRP . . . ERP is used primarily in satellite operations because it affects the transponders (not FM repeaters) I have had several private emails in response to my comments about QRP . . . I have seen folks operate the CQ WW CW contest in the QRP category with stacked beams or monoband beams . . . . I have never seen a definition of QRP that went into ERP . . . . they just use the transmitter output with all of the ambiguities that brings . . . have fun Jim W9VNE _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
-- <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><> Nigel A. Gunn. G8IFF W8IFF (have also held KC8NHF, M0NHF, 9H3GN) 1865 El Camino Drive, Xenia, OH 45385-1115, USA 937 825 5032 e-mail [email protected] www http://www.ngunn.net Member of ARRL, GQRP #11396, QRPARCI #11644, SOC #548, Flying Pig #385, Dayton ARA #2128, AMSAT-NA LM-1691, AMSAT-UK, MKARS, ALC <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb