Radio guru's help me identify this!

[cdoggwsu]

So, I just ordered a Uniden PC78LTW and I'm trying to plan out all of the CB and antenna wiring. My truck was originally a forest service vehicle and when I pulled up the original vinyl flooring I discovered two approximately 10 foot long coax cables running up through the A-pillar to two mount points on the roof. I would assume these were for CB or possibly Radius/VHF. First off can anyone tell me what type of mounts these are and second can they be used with my CB?

Sorry for the craptastic pics but I only had my cell phone and it's cold out. If need be I can rustle up the digicam and retake the pics. As always, input is much appreciated!

***PICS***

 

[pauly383]

They are NMO mounts . Go get an Antennex or Larsen 26-30 mhz antenna and slap it on after you trim it to CB frequency and you will be be CB ready .

Then use the other with a dual band antenna and radio after you get your ham license

I run two of those :

 

[cdoggwsu]

I was hopin' you'd show up, thanks Pauly! Are those center posts for tuning or do you just have to do it by trimming the whip? Oh and I heard somewhere that for best SWR tuning the length of the coax should be in multiples of 3ft. I have no idea how much is between the roof mount and where it comes down from the A-pillar, is it that big of a deal?

 

[pauly383]

The coax lenght just tricks the meter into being low . Just run the length needed . It just needs to be 50 ohms since your radio is 50ohms , and your antenna is 50 ohms .

The center thingy isn't for tuning , that is the contact button for the center of the antenna . It just pushes into the mount , or threads into it . Some antennas for those mounts have a pin that would go there if you removed the button .

 

[cdoggwsu]

Thanks again for the info! Another thing I noticed was that the Larsen antennas listed on some of the sites say they are "27 to 31" mhz even though the CB is listed as being high 26's. Aside from that the weather alert channels are listed around 162 mhz, will the same type of antenna work?

 

[cdoggwsu]

Anyone on the weather channel reception?^^^

Sorry for the newb questions!

 

[cdoggwsu]

Still looking for an answer to this

 

[ttuburbo]

You should still get reception for the weather channels. People have 1/2 and 1/4 and 1/8 wavelength antennas all the time that work for 26mhz and also get reception on 126.

 

[cdoggwsu]

Yeah, I would have thought it would work but I wanted to be sure before I bought an antenna. Thanks, ttuburbo!

 

[pauly383]

It don't take much for reception , weather is picke up on the transmit antenna just fine even if its too long .

Just make sure to trim the antenna for what you transmit on . The antennas are listed as 26-31 mhz becasue they are cuttable for any frequency in between .

They don't work on all those frequencies out of the box . Just for clarification

 

[ttuburbo]

x2 should have clarified that, Im a newb here and should read before I hit post. Pauly, you're in Mesa, Not far from me in Lubbock. Are you ever on HF at night?

 

[pauly383]

x2 should have clarified that, Im a newb here and should read before I hit post. Pauly, you're in Mesa, Not far from me in Lubbock. Are you ever on HF at night?

I should be , I just tsuck a R7 on a tripod over my garage . Just haven't gotten my room cleared out enough to really get back on the fixed station .

I have boxes of cables , radio gear , and PC parts to finish organizing and tossing out/putting away before I complete my current radio rig setup .

I barely have enough room to make ot from the door to the chair to sit here and post

Could be ready to try and QSO next week . And when I get the antenna back on my Burb , I got a RCI2950 and an antenna tuner I could work from my driveway if the 10M band opens .

 

[cdoggwsu]

It don't take much for reception , weather is picke up on the transmit antenna just fine even if its too long .

Just make sure to trim the antenna for what you transmit on . The antennas are listed as 26-31 mhz becasue they are cuttable for any frequency in between .

They don't work on all those frequencies out of the box . Just for clarification

Yeah I figured it would involve trimming. Is there a specific amount to trim or just trim to get it within SWR limits?

 

[pauly383]

Antennas get shorter as the frequency goes up , so out of the box the antenna would be lower than CB frequencies . So you would start by trimming a little ( 1/8 to 1/4 inch at a time ) to bring it to the middle of the CB band . If its as close to perfect in the middle as you can get, the outer edges won't be so bad either .