OnCor is pretty good about keep the frequecnies together and in frequency order for the most part. There are abviously some exceptions. However, enter the control frequency then press FUNC, then Press TUNE. This will put that freq in TUNE mode and you can get some immediate info like channel number and site number where Cnn is the LCN (of the control channel) and Snn is the site number. Post that info immediately so we can move Sherman from the 900's down to the 100's where it belongs in the DB.
Now, if you're lucky, the site is set up in the simplest way possible. Let's say you you've found the control frequency to be 939.475, you've entered that in TUNE mode on the P500 and it is says something like C09 S08. Then you now know that freq 939.475 goes into LCN 9 and the site number is 8. Enter 939.475 as LCN 9.
Now, here comes the "if you're lucky" part. Try entering 939.4375 as LCN 7, 939.4625 as LCN 8, and 939.4875 as LCN 10. Try tracking a few conversations and see if it tracks properly. The P500 must be signal inverted for OnCor. Most of the smaller OnCor sites are set up this way and it may very well work. If not then try moving the voice channels around a bit. UniTrunker can tell you exactly the LCNs of the voice channels but not the freqs, you have to figure that out by manually following the voice channels.
Of course, all this assumes that the FCC info is correct. If it seems like you're missing part of a conversation then search the range 935 to 940 to see if you can find voice channels not in the DB.
Russell