Hi Ron, and thanks for the reply. First off, the 904 signal is always there - and about 100kHz wide... A >>WIDE<< signal.
Second, his machine is on 927.600/902.600. As you can see, the signal is 2 MHz up and still clobbering his receiver. Mark - N9WYS -----Original Message----- From: [email protected] On Behalf Of Ron Wright Mark, Usually desense is not harmonic or intermod related. It is caused by wide band noise from a transmitter. For harmonic it is just 2,3,4, etc times a frequency. For intermod it is nF1 +/- mF2 = your receive freq. In either case the problem will be there only when the offending txs are keyed up. Is the 904 tx keyed all the time? If not then you can determine if coming from it. Listen when it is unkeyed for the problem. If it is keyed all the time then I would put your friends tx on a dummy load with the remaining parts of the repeater, duplexer & antenna & receiver, connected. This can aid in determining if your tx is part of the problem. What are the freqs of your friends repeater? 73, ron, n9ee/r >From: Mark > >OK, it’s been a while since I’ve had to compute this, so if my question seems >a bit “trivial” or elementary in nature I apologize in advance. Yes, my math >is rusty. ;-) > >Having said that, I’m trying to assist another ham with a desense problem he >is experiencing on his 900 MHz ham-band repeater. He is experiencing about >10dB of receiver desense because of a signal centered at 904 MHz. He tells me >this is verified with a Spectrum Analyzer and it is about 100 kHz wide... I >take him at his word. The site he is at has no other 900 MHz at all, but it >is a commercial site with other “stuff”, including various government and >commercial frequencies, in use. > >What I am trying to do is see if we can figure out whether this might be a >spur, or maybe some harmonic, that is being generated as the result of a mix >of other products there. > >Can anyone provide me with the math necessary to try to determine whether this >is a harmonic, using very rudimentary figures? (For example, I want to be able >to use basic freqs like 150 MHz, 450 MHz, etc, to at least get us in the ball >park.) Once we get close, then we can fine-tune the freq combinations to see >if it is a mix product. Or if anyone has any ideas, I’m certainly open to >suggestions. > >Thanks, >Mark – N9WYS > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome. ------------------------------------ Yahoo! Groups Links No virus found in this incoming message. Checked by AVG - http://www.avg.com Version: 8.0.138 / Virus Database: 270.5.1/1560 - Release Date: 7/18/2008 6:47 AM
