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CHANNEL GUARD CB FILTER


Jim,
I can't get to that 'page' to see what they say about the filter. If it's touted as being a 'cure all', then no, it isn't going to work. Just too general a statement.
Filters can help 'cure' adjacent channel interference but they are not a sure fire 'cure'. There can be too many causes for that type interference ranging from things that can screw up just the close adjacent channels, to things that can screw up the whole band. That includes the interference you hear along with the interference you might produce yourself.
Low pass filters work by curring off stuff above a certain frequency, only the stuff 'lower' than that cut off frequency get through (just the exact opposite for high-pass filters). For a filter to cut off junk except on the channel you are on, it means that there has to be two filters, high and low pass, for ~each~ channel they are supposed to protect. So, 80 filters for the regular 40 channels. And that doesn't say anything about filters in each IF stage or the receiver and transmitter. Or, the same thing can be done by the radios that are 'computer based'. But, it also means that since there would be a huge number of 'filters' involved, there would be a 'price' for them. No more $29.95 radios! It's certainly possible, just not very practical for us that ain't exactly 'gazillianaires'!
Filters do work. They are nice to have. There are exaggerated claims about everything, filters included.
- 'Doc


PS - And here's something else to think about. If it's sold on eBay, then there's someone, somewhere, that ain't happy with it. That can be good or bad, but do you wanna find out by paying for it?
The only ones who "win" on eBay are the people who are selling...
 
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Mork said:
http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewIt...38977&rd=1&rd=1


How well does this work? Is it effective in eliminating most cross channel issues as they state?
Thanks.

Jim
Click to expand...

Years back I bought a used 148 GTL that had the Channel Guard filter installed in it. Yeah, it cuts down on cross channel interference, but in my case, it did so at the expense of the receive sensitivity. Couldn't hear any kind of weak signal. My Tech couldn't get it to work right, so I had him remove it, put it back to stock, and re-align the receive. Still have the 148 today and it works great.

I can't say if the filter itself was junk or if the installer botched the job, he'd been a radio tech in the Air Force, so I'd hope he had the knowledge to do it correctly. Don't quote me on this, but I think you removed a .01 cap between two stages and installed the filter in it's place, or something akin to that.

Just my $.02, don't know if it helped you at all... 8)
 
I have one installed in a Voyage 9000. It cures the problem that -some- Galaxy radios have. The problem is that another operator on another frequency can take out someone on your frequency seemingly regardless of how much power either one is running. You can hear this adjacent channel fellow as clear as you can hear your friend. The CBC Channel guard does a very good job of fixing this problem on the radios with the 3600 series boards. I wouldn't try it on chassis that have "good" receivers already like the Cobra 148GTL. There really isn't any point.

What won't it do? Well, if you have a fellow that is bleeding across 1 MHz of frequencies, the channel guard will not operate like a crystal ball and cut out everything you don't want and let everything you do want pass. If there is a problem with the offending transmitter, the channel guard will do nothing because the offending transmitter is transmitting on your channel as well.

If you choose to purchase it, buy it wisely. Look at the interference that you are trying to eliminate and decide whether it is a problem with your particular receiver, or is it a problem with his transmitter. If it is the former, the Channel Guard works really great. If it is the latter, it don't do diddley.

Mopar
 
CHANNEL GUARD

I BOUGHT ONE OF THOSE CHANNEL GUARD BOARDS & INSTALLED IT IN MY LICOLN, IT CERTAINLY DID THE JOB & IT SAYS IN THE INSTRUCTIONS TO TWEAK THE RELEVANT TUNING CANS AT THE I.F STAGE AFTER INSTALLATION, I HAD NO LOSS NOTICABLE ON RECEIVE, LOU FRANKLIN MAKES & SELLS THOSE BOARDS ON E BAY
UNDER THE NAME OF cbcinternational & THEY ARE WORTH EVERY PENNY, DEFINETLY THE BEST CURE ON THE MARKET FOR ADJACENT CHANNEL REJECTION IN MY OPINION :D
 
i love the channel guards.

and they are VERY useful in the 148/2000GTL receivers.

the channel guard is all about channel bleedover, and it does a pretty good job of cutting down on it.

mine showed no decrease in receiver sensitivity.
it is not a cure all.
i have a local that is very close to me and runs an old teaberry that is completely hacked, driving an ancient palomar 2 pill, using a cranked D104. oh, and he constantly yells right into his mic.
i think you get the picture. LOL

well, he used to bleed on me from 10 channels away, and faintly past that.
he now bleeds on me from about 4 channels away, and faintly beyond that.
i will be getting one for my DX959 soon.
loosecannon
 
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These filters looks like the right thing. I think though they would cut off the audio highs on AM, not that most transmitters modulate audio higher than 3KHz anyways. Even with this narrow filter, a poor third-order intercept of your receiver front end amp or mixer will cause you to hear splatter on strong signals.

For SSB, you would want an even narrower filter. Commonly a mechanical filter is used at 455KHz that has 2.3KHz bandwidth. It is quite flat in the passband, and cuts off sharply outside of the passband. Unfortunately, CB radios dont use 455KHz I.F. anymore, so these mechanical filters cannot be used.

If I buy a general lee, or super-star 158edx today, for example, don't they already come with these narrow filters with the bandwidth cbcintl sells?
 
dud muck,

As far as I can tell, audio quality as far as frequency response is concerned is unaffected although I will admit I have never done a direct A/B test side by side. I run one "Galaxy" chassis without and one with the Channel Guard every day.

I do notice one rather annoying trait however. You know that ringing noise that is that a receiver has when someone is off frequency on AM along with others that are on frequency? Well, the Channel Guard can, in certain situations, enhance that noise almost to an annoying degree. Especially if you have a vehicle that introduces a slight amount of noise along with everything else. I happen to drive a truck that has a slight computer noise problem. The radio in this situation is almost too annoying to listen to. My radio can sometimes ring most of the night. ARRG! If you have the Channel Guard, you can pick out off frequency radios in a heartbeat. You can really tell that it is doing its job. When you swing that clarifier, signals are nearly gone in about 3 or 4 KHz.

Now, that being said, I probably wouldn't notice it as much if at all if I used the radio as a base. But, having it in different trucks and driving past very busy truck stops with very poorly tuned radios running rampant everywhere this trait is fairly obvious.

Mopar
 
if I was so picky when it came to a radio I would have been gone a long time ago. Filter this and filter that , TVI here and TVI there ect. ect. ect. 20 years into this hobby and looking for perfection has past me by a long time ago . But then again IM only a CB'er on the dirtest band in the land. I've had many of the radios mentoned in this thread concerning the 11 meter band as my home and they all worked good enough for me. If I was such a perfectionist when it comes to the dirtest band in the land , they would have had to fitted me for a stright jacket by now. But then again , if I might have had the extra money over the years , maybe I could have spent more money (or wasted it) on some even better gizmo to make the radio that already worked great for me to begin with , even better ? Must be nice to have the extra greenbacks in life. Wow !! maybe if I was richer I'd be more closer to being perfect ? Go Figure
 
Highlander_821 said:
Musicman, meet Switch, the resident curmudgeon.

He doesn't like it when people have negative feedback about radio retailers, either.
Click to expand...


Rather rash I would say Highlander , I'd say your handle fit you just fine. (As in High Horse) You feel the need to slander any retailers or "Me" to make you feel more important and that you are doing the radio world a favor ? Be my guest . You are what you are ........A curmudgeon , You looked in the mirror lately ?
 
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