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 <[EMAIL PROTECTED]> >Date: 2008/07/17 Thu PM 03:11:13 EDT >To: [email protected], [EMAIL PROTECTED] >Subject: [Repeater-Builder] Harmoinic products > > >OK, it’s been a while since I’ve had to computethis, so if my question seems a >bit “trivial” or elementary innature I apologize in advance. Yes, my math is >rusty. ;-) > >Having said that, I’m trying to assist another hamwith 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 centeredat 904 MHz. He tells me this >is verified with a Spectrum Analyzer and itis about 100 kHz wide… I take him >at his word. The site he isat 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 whetherthis might be a >spur, or some maybe harmonic, that is being generated as theresult of a mix of >other products there. > >Can anyone provide me with the math necessary to try todetermine 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 canfine-tune the freq combinations to see >if it is a mix product. Or ifanyone 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.
