Uniden PC 78XL (same as Cobra 29) Noise Blanker Problem

[loosecannon]

cool deal!
glad it helped.

what part number was the ANL diode in this chassis?
im aware of the detector, and NB diodes, but ive not changed any diodes in the ANL circuit.
info please.

the relay and battery noise generator is not in the hackers guide as i stated earlier.
its in the second book of that series called, "cb radio modifications and secrets." same author.

you can get both these books on ebay for about 7.00 each.
great price and cool books.
at least you could get them two months ago when i last saw them on there.

the noise generator is just a 9 volt battery and a 9 volt relay.

hook the negative of the battery to the negative of the coil on the relay.
jumper the positive of the relay to the common terminal, and connect the battery positive to either the NC or NO connection. cant remember which.
at least i think thats the way it went together.
cant remember right now, but it is just two parts; the battery and the relay.
later,
loosecannon

 

[CollinsMan]

Loosecannon,

Thanks for the information on the books - I'm going to pick them up, soon!

The ANL diode is a 1S2075. I wasn't sure if the Schottky was compatable or would do any good, but I figured it wouldn't hurt to try it. So, I did, and the results were fantastic! It is D7 in my Uniden PC78XL, and should be the same in a Cobra 29 as far as I know.

The 1S075 has a 8 nano-second recovery time (I believe), and the 1N6263 I replaced it with has a 1 nano-second recovery time. Thererore it is much faster when responding to peaks. This makes signals (especially over-modulated ones) much "clearer" and less "fuzzy" to my ears when the ANL is enabled, and it still stifles a good bit of the line noise, etc. The NB takes most of the rest if I need to activate it. Bear in mind that your mileage might vary, etc.

I also replaced the ANL diode (and AM detector) in the Lafayette HB 640 that I got from SwitchKit with 1N6263s, and it made a great difference with that radio also. So, I would think that other radios would respond similarly.

I'm gonna build that noise generator; I'll bet it works well, and I'll be able to let my wife use her hair dryer in peace!

By the way, I got the Uniden Madison and MFJ noise phasing device in from Canada yesterday. I'll post concerning how well the noise phasing device works this weekend when I get a chance to use them.

73, and thanks for your help!

 

[CollinsMan]

Hi Switch Kit,


"I personally wouldn't deal with noise for very long , I find it to be very nerve racking and would work on giving me a headach most of the time."

I hear you! I hate noise, too. That's why I like to modify CB receivers for better performance.


"I think it's great that others can take and have the time to change things around for the better when it comes to there equipment ,in many cases , it may not be worth it to me , but as long as it is worth it to you , that's all that really matters."

I understand where you are coming from. However, modifying receiver sections in CBs is relaxing to me. Sort of the same thing other folks seek to do when they work crossword puzzles, watch football games, or tinker with puzzles.

I have transceivers that I use for normal listening, and a couple of shelves of radios that I "tinker" with when I have some spare time.

For example, that Lafayette I got from you is going on one of my shelves. One day when I need to relax, I'll put it on my work bench and modify the receiver section, and do a complete alignment on it. After doing all that, I'll be all relaxed and Smurfy! It's just one of the things I like to do.

Have a great week, and 73!