Acceptable Coax Resistance?

[rogue909]

So I got my first CB radio to install in my suburban! ^_^ But I seem to be having some issues...

I currently have a Firestik antenna installed to a Diamond K9000 motorized mount. I opted to ground the antenna to the roof of the suburban and hooked it all up to my Cobra 29 LX.

When I hooked the antenna up to the radio I get a warning from the radio regarding the antenna when I attempt to calibrate it (I was just following the instructions from the radio for calibration...). I popped out my multimeter and measured the resistance between the outer shield and inner wire and found a resistance of 600k ohms. It's my understanding that is supposed to be an open circuit. But being a noob here I'm not exactly sure how "open" the open circuit needs to be. IE; should the multimeter simply read no connection ("0 ohms")? Or is 600k ohms open enough??

 

[Blackswan73]

You are measuring the wire in the Firestik, and if you are touching the leads, your body. Disconnect the coax at the antenna, and repeat measurement. Reading should show open. Make measurement on the Rx1 scale.

 

[N4GIX]

It sounds as though there mad be a "whisker short" in your cable connector(s).

 

[rogue909]

That measurement was taken with the wire disconnected from the mount and antenna.

 

[kf4eyr]

you need to use an external swr meter,,,, to check swr.... most swr meters built into radio is very inaccurate,,,un hook coax from radio and antenna mount and check with with ohm meter should show short,,, if it doesnt there is a cut in the coax or the pl259s are not put on right,,,,make sure any of the antenna is not touching or is close to metal roof rack and such........

 

[JayMojave]

That measurement was taken with the wire disconnected from the mount and antenna.

Hello R909: I would think that the resistance reading between the center and shield should be "OPEN" that is no reading or resistance measurement being No Ohms. Its a possibility that you are measuring the resistance of your fingers/hand with the meter, as said here before, make sure your on the RX1 scale.

If your meter indicates resistance on the RX1 scale while holding a meter lead in each hand, says the meter may have been on a resistance scale while Voltage was applied to the meter. I myself have done this many times, not paying attention.

The coax and antenna mount should have a low resistance ( 1 to 2 Ohms) measurement from the center PL-259 radio end connector to the antenna mount center. And the same low Ohm measurement from the shield / outside of the PL-259 connector to the antenna mount part that connects to the body. The Shield of the connector radio end should have a low Ohm measurement to the vehicles ground or body.

Your radio is telling you the antenna is not right some where. Its hard to give good advice not being there to see it and test it. It sounds like one of the coax connections from the radio to the antenna is open. Does the radio receive local stations?

What type Firestick antenna do you have ?

Jay in the Great Mojave Desert

 

[jim202]

It might be better for you to to measure the coax alone like someone else has mentioned. But I would put a different twist on it. This might take clip lead and a section of wire on the RF connector end from one wire of your meter to the center pin of the coax connector. Then take the other meter lead and go to the antenna end of the coax. Disconnect the coax from the antenna and make sure you have close to zero Ohms on the center conductor. Then do the same with the shield.

Many times over the years when people have come to me, I have found either no connection or a very poor connection on either the center conductor or the shield of the coax to the radio end connector or at the antenna. Someone forgot to solder the center conductor of the coax to the center pin of the RF connector at the radio end. Or there is a broken center wire at the antenna end.

It is easy to test and only takes a few minutes. But it can save you from hours of frustration trying to figure out why your antenna isn't working. Don't forget to test the jumper of your SWR meter if it is external to the radio. That jumper could also have a problem.

 

[ElroyJetson]

You need a meter made for measuring RF cables. The only thing your multimeter is useful for is to ensure that you have continuity from one end of the cable to the other, center conductor to center conductor, and shield to shield.

For trying to figure out of the cable is any good in any other way, a multimeter is USELESS.

Reason: The cable is designed to provide a specific impedance at RF frequencies, NOT AT DC.

 

[wyShack]

I would say 600,000 (or 600k) Ohms between the inner and outer wires is for all practical purposes an open. next step would be to measure center to center and shield (or outer wire) from end to end. That reading should be 0 (or less than 1) Ohm indicating a short-actually just that there is no 'open' in the wire. if those check out, it is time to look at the antenna. That can be a problem as many antennas will actually show as a short at DC (how the meter works) even though they present a impedance of 50 Ohms at 27 Mhz.

If the coax checks out, measure SWR on channel 1 and then on channel 40 and follow manufactures instructions on adjusting the antenna.

Hope this helps

 

[JayMojave]

Hello R909: Looking at the manufactures specs for the K9000 Mount, it says:
"Accepts "Ground Independent" antennas up to 45" in length"

See: Diamond® Antenna ~ K9000LRM Motorized Luggage Rack Mount

This might mean that there is no connection from the antenna mount to the vehicles body, and this would certainly cause a high SWR as your radios has the antenna alert on when transmitting.

Also the Firestik web page says to use the NO GROUNG PLANE antennas only with there coax harness.

See: CATALOG Main Page (Frame Setup)

So this may mean no matter what Firestik Antenna you use, it may not work with the K9000 mount. Also the Diamond K9000 Spec sheet calls out only using duel band VHF and UHF antennas for the Ham Bands, 2 meters and 70 Cm.

Suggest trying a different mount for trouble shooting, maybe the Firestik mount made for your antenna.

Let us know what you find out there. Good luck.

Jay in the Great Mojave Desert

 

[Rred]

If you grounded the ANTENNA rather than the MOUNT, to the roof of the Suburban? You totally got it wrong. That antenna MOUNT is for use with antennas that have a built-in counterpoise or ground, i.e. a base loading coil or dipole.
The Firestick ANTENNA is simply a helically wound vertical whip, it has no ground or counterpoise and requires being use with one. If you connect the coaxial cable's SHIELD to the Suburban's roof, that ma be good enough, since the shield is normally connected to a ground plane at that point, and presuming the Suburban still has a metal roof, that will work nicely. In theory you need a bare metal to metal connection, but in practice, at radio frequencies, it may work through the paint if the connection is clamped tightly.
You might ask the folks at Diamond if they can recommend a handy grounding point, or a base loading coil to use in these situation, but I think grounding the coax shield directly to the roof (or luggage rails if they are metal) will probably get you in the ballpark.

 

[wa1nic]

Firestiks are intentionally too long as shipped and need to be adjusted for an acceptable SWR at first installation.

You don't have to take my word for it... the Firestik web site will tell you the same thing.

 

[JayMojave]

Hello All: A reply from the Op R909 would be in order. A lot of guys come out here asking for help and such and a lot guys try to help. Many times we don't get any feedback to questions or suggestions.

Its difficult at best to help someone out NOT being there, and only going by the words in the threads first posting. It would certainly be a curtsey to reply about the trouble shooting effort.

Jay in the Great Mojave Desert

Kreedentials:
Passed Traffic school, only took twice this time No Kolledge credits
New Left and Head Gasket on 64 Buick, no leaks
Voted last time, and even found the right place
Even Louder and more Bodagious PA System in 4X4 F250 400 HP Truck, watch out ladies on cell phones
New 5 element beam antenna at 75 feet, no damage from last wind storm

 

[wa1nic]

Jay, I traveled thru the desert on a horse with no name (a big military prototype truck, on its way to the 29 Marine base.

110 F today ? ;-)

 

[JayMojave]

Hello Rick / NIC: Our part of the Upper Desert (Mojave) is at and around 100 Degrees F which isn't to bad as compared to 112 Degrees that it was for a few weeks. These lower temps seem livable and some what comfortable.

I checked the 29 Palms weather for today and it says the high will be 104 F. Barstow will 101 F.

What big truck type are you driving, have worked on a few and driven a few. Good friend in Idaho wants to sell me his Duce and half with big snow play, CB, and a few Ham radios, all ready to go.
I want it to cruse for chicks.

Jay in the Great Mojave Desert

 

[MisterLongwire]

<---- ROFL
I prefer the Buffalo.....drives through EVERYTHING

 

[wa1nic]

It was an International DT4300 (26,000#), outfitted with a 30 KW alternator that I headed the design team for. When time came for the marketing people to demo it, none of them claimed to be able to drive a manual transmission so they all flew first class air and myself and another engineer had to drive the truck there ourselves (from Massachusetts).

We ran it out in the desert for 8 hours a day, 5 days a week, making 30 KW the whole time (with no failures). It was in August (the Marines selected that month on purpose). It went over 110 F every day.

My daily driver is a 2014 F350 dually flatbed, so it wasn't totally foreign to drive the bigger truck.

 

[JayMojave]

Hello Rick / NIC: No response from R909??

That's funny that marketing personal for heavy machinery could not drive a clutch. But sounds like it got you out of the office and such, good for you. I love little off the side road trips.

Wow 30 KW tilt!

A design Discussion / Brawl broke out in the hall way a year or so ago, about a new truck design (5 ton truck) needed a electric winch or Hydraulic or Power Take Off winch. The head dude a old experienced hands on, and shot at Vet, and hard core type had invited me and a few others into a meeting on the winch design. It seems the lesser than B itchen types wanted a electric winch, for ease of production and cost. Watching the fireworks from right in the middle of the meeting room, I didn't get to say anything as it was all being argued by very informed and experienced hands on engineers, that a power take off winch was the only way to go as its worked well since WWII and on. Also the selected winch was a on the fence of working due to it size and current needed to operate with the supplied battery and alternators. As is in most four wheel drives, it works but may not get you out of a spot requiring a long time usage.

We went with the power take off winch, and larger alternators, but lost the demo competition. I am sure if we included a neat AM/FM radio to rock out to, and air freshener hook on the mirror we would have won.....

Nice truck I have been looking at the new trucks for a few years now. Is the dualy really worth the added cost?

Jay in the Great Mojave Desert