On 30/12/15 22:24, Marcus Müller wrote: > Hi Daniel, > Cannot stress this enough: > Don't try to do everything to the max right from the start. Sure, 100mW > is a lot less than what can do in the licensed bands, but then again, > not coming from an amateur background, 120W right out scare me. Please
Maybe some clarification is in order: - need to check if the power amp's output is proportionate to the input power - does the USRP and GNU Radio provide a way to manage output power (power into the amp), or is it always constant at 100 mW? - it is legal - e.g. 400W is the limit in the UK and regs are similar in other countries for fully licensed hams: http://www.ofcom.org.uk/static/archive/ra/publication/ra_info/br68r11/br68.htm > make sure no more than -15dBm are fed into the USRP RX. So at an output > power of 120 W ~= 51dBm, you need isolation of at least 66dB between > your TX antenna and the RX port of your USRP for the TX frequency. Also, > considering you're buying a device that can potentially cover 70MHz to > 6GHz, spending lots of money on a powerful amplifier that can but > operate on a few MHz really sounds like an unbalanced investment. Maybe > reduce the output power (unless you want to do moon bounce, maybe), and > get separate filters, just to keep the option of not operating in > 144-147MHz; your whole operational range is much smaller than the amount > of spectrum you can control with the USRP at once. > Agreed - many people would be satisfied with something up to 50W, similar to a mobile rig, this was just the first thing Google found when I included "100 mW" in my search query. I have had SAREX contacts with 5W from a handheld device and J-pole, but that was in Australia where the population is very thinly distributed and I could have been the only person transmitting. There were no nearby mountains (unlike my current QTH) and no tall buildings. In a densely populated region like Europe, more power may appeal to some people. > Of you're not going to use two highly directive antennas for RX and TX > to achieve isolation: > You will either need an RX/TX switch (that you should definitely control > using the USRPs GPIO pins, which can be programmed to certain states > when transmitting, receiving or doing full duplex) to isolate RX from TX > when transmitting, or an extremely expensive circulator-based device. > > To be honest, you seem to be throwing money at your problem, that partly > including having a bit of uncertainty what you want to do. I'd rather > start small, buy the USRP, and maybe a preselective filter, experiment a > bit with "short links", then invest in antennas, filters, switches and > or amplifiers as you build up wishes and experience. > My feeling is that you'd probably want to first RX only on different > bands with different antennas, see what's possible with and without > preselection, then decide on one or two bands, get more specific filters > for these, switches, and then an amp. > Don't start with something that you can use to defrost your antenna, and > then try to figure out where you fried which parts of your rig. Thanks for this feedback, I wasn't going to go out and buy this first, I just wanted to start putting together a vision of what the big picture looks like and what all the pieces will cost. Buying an amp that can fry an egg is a poor substitute for having the right antenna. On the receive side, this fact is obviously even more unavoidable. Regards, Daniel _______________________________________________ Discuss-gnuradio mailing list [email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
