BCT15X: Uh Oh - Front-end Overload?!

[W7BJH]

I have a Uniden Bearcat BCT15X in my pickup and during a hunting trip earlier this month I'm afraid I may have overloaded the front-end while running some power on one of my amateur mobiles; it appears that I've lost all VHF/UHF recieve on the BCT15X. I tried scanning the 11m band and it hears good there, but I've tried the FM broadcast band and scanned memories up in to the 460MHz range at minimum and nothing heard even when broadcasting right next to it.

So, question is, can this be fixed by a study hand and a hot iron or should I write it off and be more careful next time?

Regards,

BJ
W7BJH

 

[n1chu]

Generally speaking, with reasonable power settings, you shouldn’t damage the scanner unless you have spliced both into one antenna! But you haven’t told us how much power you were running. Does it hear the National Weather Service? Have you swapped out antennas?

And, no. A steady hand won’t fix it unless you can visually determine what needs to be done… something like a bad or broken solder connection on the antenna input.

In the event you can’t fix it yourself you need to determine if the cost of repairing it (Uniden charges a flat fee at a little less than $100) is going to save you money over the cost of a replacement unit.

 

[W7BJH]

If it was in fact the 2m rig I was running 50W through an antenna mounted about 4' away from the scanner antenna. The amateur radio antenna is a dual-band Diamond with nominal gain, the scanner antenna is one of those little stubby mag-mount types that is hard plastic cased and only about 4" tall.

The other potential cause was my 10m rig which I ran about 250-300W thru at one point trying to make a contact, this antenna is mounted closer to the scanner antenna.

I haven't tried the NWS frequencies, I will, but I did try a couple of antenna/feed line combos.

I've got several pieces of equipment that could help me troubleshoot; spectrum analyzers, o-scope, service monitors, signal generators... but I'm pretty green still when it comes to using them... maybe this would be a good project to learn on, if I fail its not the end of the world.

I've read that these particular scanners have pretty sensitive front-ends, but I've sure like it, hoping I can salvage it and save myself nearly $200 and maybe learn a little something along the way.

 

[Ubbe]

I tried scanning the 11m band and it hears good there,

There's protection diodes directly at its antenna input that conduct over 1,4 volt peak and there's switching diodes for the different bandfilters. One is 25-54MHz so if that works it is diodes that need to be replaced. Probably for those bands that where scanned during your transmit. If you have a RF signal generator you could check if it works nomrally in low-VHF and then check the other bands.

Or if it is AM mode that works and not FM then that indicates the amplifier transistors that have been damaged.

Those band filter diodes are covered in epoxy as well as some other components so could be tricky to perform repairs. Those amplifier transistors and protection diodes are easy to access. Schematics are available.

What does a new BCT15x cost, $125?

/Ubbe

 

[n1chu]

Well, scanners front ends are not necessarily sensitive (selectivity vs sensitivity) but they are wide band receivers. I expect you are using the term “sensitive” as a descriptive word meaning susceptible, which would apply to our basic understandings of how these scanners actually work. You’ve got the necessary equipment to test but not the needed understanding of how a radio works. That equates to my buying a car without knowing how to drive! Neither scenario works.

I’d log onto the regional forums (they are listed by state) and see if there is any expertise that could meet up with you. Other than that. It’s back to repair or replace. I choose which to do by determining how much a replacement costs new. I’m not going to pay almost $100 to repair when for $50 more I can replace it with new. Of course other factors such as age factor into it when the cost new gets to be too expensive.

 

[G7RUX]

Just for future reference, Schottky diode limiters are available quite cheaply that should help with avoiding a repeat in future.