If the 785/6 are anything like the BCD-780XLT, they may even be easier/better to modify than the newer models.
The BCD-780XLT actually had two 450Khz IF filters installed at the factory!
They had a 50D and a 50F installed. Presumably, these were for FM and AM respectively. I can't confirm this, but it is conceivable that FMN was also piped through the 50F filter, along with AM.
If so, there may not be much point in modifying these radios.
The inclusion of the 50F filter is probably why so many people prefer these radios over the newer models for AM reception.
If FMN is not piped through the 50F filter, the radio would certainly benefit from replacing the 50D filter.
R
I also cannot confirm this for certain but from actual testing by ear, I can't say NFM mode does anything over FM mode.
If you ask me, they use the same audio filtering trick when changing modes from FM to NFM in the 780XLT's as they do in the newer digital models.
I had (have) adjacent channel interference that a properly working narrow filter will totally eliminate in an Icom R-7000 thru 9000 but changing to NFM on the same frequency in the 780 results in no noticeable change at all on the 780.
AM mode does appear to use the other filter so that helps for AM reception.
It's really a shame Uniden did not add electronic filter switching of wide and narrow filters in the triple conversion and later models.
I'd guess on a mass scale, it would have cost them a dollar for the models that have selectable FM bandwidths already. The signal line is already there to drive a circuit to make the switch.
And doing it with proper circuit traces would eliminate any problems of unwanted noise or signals being introduced at the filters leads as they would still be surface mounted and probably right next to each other with only a diode switch between them.
I noticed that almost all scanners did not really have a narrowband mode long before they announced the narrowband mandate.
I think Uniden is relying upon the fact that the frequency coordinators are not supposed to put a new narrowband channel right next to an old wideband channel unless the stations are seperated by a decent physical distance.
Something tells me that will not remain true in cities with severe bandwidth issues!
Then there is even a future reduction in bandwidth planned in the not far off future. Basically that one will again reduce the bandwidth by half or 6.25 kHz I think. Some radios are already capable of that narrow bandwidth.
I hope that one goes smoother than the current bandwidth reduction did.
I saw a licence app the other day for a town somewhere that was applying for a narrowband change on VHF low band!
Unless there is something in the works to narrowband low band, I think someone was misinformed and does not know that low band does not need to be narrow.
I forget what city or state that was in.
The only thing I could figure is they were using some type of dual band VHF hi and low radios that shared the filters and in order to narrowband their high band frequencies, they also had to narrowband the low band section.