Cobra 29lx questions?

Steve, unless whatever vehicle you drive in is exceptionally quiet, the folks you talk with on the radio will appreciate the noise cancelling function. It keeps the other person(s) from having to try to pick your voice out from your be-bop radio, a/c blower fan, engine noise, tire rumble, other people in your vehicle, horns, open-window noise, etc.
It *is* worth cleaning the lip guard and screen frequently, since they spend so much time against your mouth....
But until the element degrades, that mic is good for "communications grade" audio, in lieu of "broadcast grade" audio.
If you're using the radio at a base station, the stock mic will sound more hi-fi.
73

 

A good tech can fix your RK56 most likely. I have 3 Astatic noise canceling mic with the RK 56 step-up transformer in them. Essentially RK with the Astatic body and switch.

 

You can always run the Astatic RD104E Road Devil Noise Cancelling Amplified 4-Pin CB Microphone on that Cobra. I run one on my Lincoln. Great audio and no background noise. You can find them on the bay for about $30-$35 shipped.

 

The problem with mounting to plastic is 2 fold, first make sure it is substantial enough to support the weight of the radio, if so fine. Second yes it is wise to ground the radio chassis' You can simply attach a extension from the negative wire running to the radio to a case screw on the radio, when possible use a internal / external lock washer on grounds. Do not run a bunch of separate ground wires for your radio, it could cause a ground loop which is a whole different subject. One ground 12-14 gauge ground from the chassis or neg battery of the vehicle to the radio chassis, neg black wire to the radio and to the antenna mount.

No problem with the antenna, good choice. Adjust antenna length to SWR to 1.5 or less.

RK 56 is a good mic, there is a rubber pad on the mic, it goes against your top lip, its called a lip guard. turn your mic gain all the way to max. Or Astectic Noise Cancelling. Im not a believer in pre amped mics, just do not see a need.

See explanation above. You should not need an extra ground, but if you do extend it from the chassis ground of the radio.

This has been a thing of much debate here, so heres my option from the commercial radio world, I am a armature (does not count necessarily for my radio opinions.) also a FCC/NABOR grandfathered license tech. experienced in Business/Broadcast TV and FM / Repeaters, so you may get conflicting opinions here. What to test, voltage, make sure you have 13 volts (battery voltage) to the radio at the connector on the red wire. Make sure the black wire has a good clean connection to vehicle ground or negative side of the battery. Make sure your coax does not have any shorts between the shield and the center conductor and both wires have end to end continuity. Make sure the antenna connections at both ends are clean and secure, finally check the SWR, I have found the meter in the radios to be very reliable unless a golden screwdriver has been used in the radio.

You did exactly right, I never coil (cause the formation of a RF choke) coax, on CB installs I never cut it to length, no advantage to cutting it line loss is so low it is not worth consideration at this frequency. There are people here who love telling others to cut it, just no reason.
Hope this helps.

 

Powder, I was nominally with you up until that point.

There's an oft-quoted line from the Wilson Antennas site in which some Professor Emeritus in EE ("emeritus" means "too old to keep on full time & salary") who says that coiling up spare coax will make a choke, which will reduce the wanted RF out the end of the coax. Seems like an awful lot of people have read that line and taken it as Gospel.
<sigh> Sure, you can make a "choke balun" for use at the feedpoint of a balanced antenna (Yagi-Uda beam, quad, Inverted Vee, half-wave dipole) if you're feeding them with coax and need to both make the transformation from an unbalance feeder (the coax) to a balanced antenna. When the shields of the windings (typically on a piece of PVC drain pipe) are arranged adjacent to one another, close-wound, and then using the right method of connecting the "antenna end" of the choke balun to the antenna. That both makes the transition and drains off any common-mode radiation that would otherwise travel along the outside of the coax shield, making it into an unintentional radiator, and maybe even on unwanted harmonics of the fundamental frequcney. Chokes are also used inside radios so that DC can be applied to the collectors (or anodes) of transistors and tubes but block the RF being generated or amplified from being diverted from the output network and instead traveling down the B+ feed line and getting into the HV power supply.

But there's nothing you can do, and especially nothing bad, to the signal that squirts out the end of a coax by simply making a coil of the slack coax. If it *were* somehow to have its coils arranged neatly with the braids soldered together (unlikely, frankly in a random hank of coax), it *might* serve as a choke -- to keep the stray RF off the *outside* of the coax, where such RF would be doing nothing of benefit, and likely spraying into vehicle electrical systems, etc.

So folks -- do whatever you want with the coax that's longer than what you need to reach from the radio to the antenna, plus leaving a foot or so at each end to replace the connectors that will come off eventually as habitual meter fiddlers put devices in and out of the radio and antenna circuit. Eventually, those connectors will go to the Happy Hunting Ground, and if there's no spare slack to pull and connectorize, you'll rue the day you skipped leaving any convenient spare coax. Cutting off 5 feet won't save enough signal on either transmit or receive to make any difference. Nor will putting on an additional 10 feet to make the reach you need, as long as you do it with one run, or decent connectors for a junction. Loss figures for virtually any coax at 30 mHz are negligible.

For reference, I have a 135-foot run of RG8-X direct burial from my shack window out to a multiband vertical antenna that's ground mounted and has a pretty extensive wire counterpoise array. My measured loss at 29.6 mHz is less than 0.5 watt with 105 watts (true CW -- dead carrier) input. And, of course, the loss is less on the lower bands.

For reference/bona fides/C.V., I've been a ham for over 50 years (20 wpm Extra), a CBer for over 45, and a commercial radio tech with (originally) 2nd Phone with ship radar endorsement (now a GROL) and a NABER certified tech. I've been actively involved in the installation and maintenance of commercial paging, radiotelephone, and two-way radios for 50 years. I've watched radios go from tubes with dynamotors or vibrator power supplies to generate HV DC in mobiles, to frequency agile spread spectrum transceivers that can be disguised inside a pack of cigarettes. And still, the same physics dictates how RF propagates.

And all of my gear gets calibrated and certified by N.I.S.T. certified labs annually. Even "the trade" no longer requires it, several of my "gummint" customers require it, so I bite the bullet and spend around $2,000/year to keep the gear in-spec.

Sure, there's a proper way to make a choke with coax. But just making a coil/hank as dissuaded by the Wilson site is misusing a term to make it seem like a *bad* thing. A properly applied choke in an RF circuit can only benefit radiated spectral purity -- but a random hank of coax *doesn't* constitute a choke, of any kind.

Well, maybe just a choke of common sense....

Hope this helps,

73

 

The new Road King mic's are crap they where sold out quite a few years ago and the Chinese company that bought them started using cheap parts in them. You want to find a Road King that has Turner Telex stamped in the back of the case.
Same thing happened with Astic. A static will still show made in the USA but don't let that fool you. You want the ones that have Cincinnati,Oh stamped on the back.
You can find them on ebay.

 

If you have a steel roof and the antenna s mounted to it you do not need to run the extra ground wire, just make sure you have a ground wire between the chassis of the radio and the body.

As far as the balum, I never read it just ground that problems existed, and found it caused a magnetic coil unless you fold it in half so you have current flowing in both direction canceling each other out.

I have made balums for antennas systems out of forming coils out of coax, frequency determins the amount needed and the diameter of the coil. I still feel its best just to stay away from things that have caused me know problems in the past. No theoy to this attitude just pain and sweat....

Good Luck in the up coming New Year and God Bless.....

 

I'm looking at either a Connex 3300HD or General Lee

I've heard good things about that mic before. Another plus for the General Lee, seen it for $199 including that mic.