tuning the CB radio

[bikrbill1964]

Has anyone ever heard of the Honda CB radio being tuned for peak output?  I used to be big into CB's when I was much younger and having a CB radio tuned improved the output range of the radio.  Since the Honda CB appears to be in a sealed box, I wasn't sure if it could be opened up and tuned.  If anyone has any info on this topic, I would appreciate the help.

Bill Brown
Newport News, VA

[Joe Hummer]

Typically "tuning" the radio is checking the SWR on the antenna.  Radio Shack has the SWR Meter but you may have to make your own cables as the the Honda CB Radio uses standard radio "banana" style connectors instead of the BNC style connectors. 

The idea behind the SWR is to get as low of a signal as you can.  You put the meter inline with the antenna and set your reference.  You then flip the switch to test and key up the radio.  If your reading isn't close to 1.0, then you trim a small portion of your antenna and test again.  You will have instructions with the meter but you can also find information about it online. 

Joe

[9Ball]

Yes, I've tuned my antenna and a few friend's Valkyrie antennas.

I bought an SWR meter and the various adapters from Radio Shack.  I used a hack saw to cut short lengths off the top of the antenna (actually from the bottom of the top piece after you loosen the set screw and pull the top whip off) until I got the best SWR readings.  It didn't take too much trimming to get the SWR to 1.0 (or close).  You will never get it perfect, but from my understanding anything less than 2 is adequate.  I got it almost perfect on channel 19 and channel 9, and between 1 and 1.5 at both extremes.

There might be posts in the tech archives with the part numbers for the adapters and cables that you need.  I seem to remember spending about $38 for everything.  Some have had their local truck stop CB shop do this, but it is very easy if you have a little patience and the right tools.

Good luck...

[sugerbear]

CB's are at max 4-5 watts. to make a difference in the received signal you would need 4-5 HUNDRED watts. a difference of 2-3 watts makes no difference. if you can be heard from 1-2 miles it's all good. the most important thing is have the mic impedence matched to the radio.
if you go to J&M website you'll see mics for honda and mics for harleys. a harley mic doesn't work well on a honda system or a honda on a harley. different impedence.
if you add a linear of 500 to 1,000 watts you'll need to move the antenna away from you.

[Gryphon Rider]

Assuming all the parts are a matched set as they came from Honda, is there really anything to be concerned about?  Wouldn't Honda's supplier (I think it's Clarion) have matched the CB head unit with the cable length and the antenna length to get near ideal SWRs?  Jrhorton, what SWRs were you getting before you started fiddling?  My understanding is that while 1.0 is ideal, anything 2 or less is acceptable.

[Joe Hummer]

Gryphon,

Ideally, yes...the systems would be matched at the factory but I doubt that actually happened.  Remember...the CB was an add-on feature...possibly done at the dealers. 

Joe

[9Ball]

Assuming all the parts are a matched set as they came from Honda, is there really anything to be concerned about?  Wouldn't Honda's supplier (I think it's Clarion) have matched the CB head unit with the cable length and the antenna length to get near ideal SWRs?  Jrhorton, what SWRs were you getting before you started fiddling?  My understanding is that while 1.0 is ideal, anything 2 or less is acceptable.

mostly 2 to 3...tuning made a huge difference.  Trust me, these are not optimized as is.  You might get lucky to get a good SWR, but that was not the case on any that I worked on.

And yes, from my understanding 2 or less is adequate.  Mine is near perfect...

The only trouble is that now my wife and I use helmet communicators (Scala) and the CB is mostly not used.  I keep it for potential long solo trips as a safety feature.  Listening to channel 19 is eye opening with all the bad behavior of the day-to-day users, mostly truckers on the interstate, and the immature ramblings and noise generators they use.  Channel 9 still has a viable function as an emergency contact channel...but with a cell phone and GPS unit the CB is not as useful as it once was.  Works OK for group rides when others have CB...

[Blackduck]

When tuning in an antenna don't cut the main rod until you have it sorted, you may need to to go longer.
I just trim the wire or braid, depending on how the antenna is made.
You don't even need to cut the wire, just wind it back over it self at the tip. That way if you need to lengthen it just pull the wire back up.
Tune at the upper and lower frequencies and the middle ones will be right.
They may have been set up matched at the factory but installation to a vehicle can put them out.
Best not to have any metal close by above the antenna base.
Cheers Steve

[Bagger John - #3785]

There are two internal adjustments for the Clarion OEM CB which will make it more usable:

One sets the squelch threshold, so that "fully squelched" actually is.

The other sets the mic gain.

Clarion pulled a good one with both the Standard/Tourer and I/S CB chassis - for that matter, the GL1800 CB as well: They spec'd a 5w-output final transistor. What this means is that if your wattmeter shows 4w output when transmitting carrier only, you're not going to get much modulation headroom as a result...and won't sound very loud.

Two ways to fix:

1) De-tune the final amplifier circuit for no more than 2w indicated carrier (into a 50-ohm dummy load) then set the mic gain pot to ~85% modulation, measured on a scope.

2) Change the final amplifier transistor to a 2SC1969, NTE236 or equivalent 13w/30MHz device. Then adjust un-modulated carrier to 4w and modulation to 85%, again with the aid of a scope. Though I cannot confirm this without the aid of a schematic (which Clarion is unwilling to provide), I think the set uses so-called "low level" modulation. There's just not enough audio drive power available to get 100% modulation - even with the 5w PA transistor - but headroom is improved sufficiently to warrant investigating the switch of PA devices.

The old Tech Archives has a post or two with the photos identifying the trim pots in question. They're VR102 and VR103, if memory serves correctly.

When I opened the first of several of these radios to see what the deal was regarding PA tuning and "muffled modulation", I couldn't believe what I saw with regards to observed carrier power and modulation envelope. Then I heard tales of a couple shops offering 'tweak and peak' services, the likes of which are done to garden-variety consumer CB rigs. It seems the radios I examined had been "serviced" by one of these shops, and they should know better than to tune the carrier all the way up to the max rating of the RF PA device. Re-setting the carrier and modulation adjustments fixed the muffled audio.

All this assumes a properly matched antenna. I try to get the tuning to less than 1.5:1 across the band and use an MFJ-259 or similar antenna analyzer for reflected power and impedance measurements. This saves a lot of cutting and adjusting.