Hungary Bill (Forum Supporter)
Hungary Bill (Forum Supporter) GRM+ Memberand PowerDork
9/7/21 3:05 p.m.

I bought a Midland CB unit secondhand, and it came with an unmarked black box:

 

 

It appears to be labeled as if it were directional, there's no significant resistance through the center conductor, and the connections are the same size and thread pitch on either side.

Aside from extending my coax cable 2.5-inches...  what might this thing do?

paddygarcia
paddygarcia GRM+ Memberand Reader
9/7/21 6:27 p.m.

Maybe some kind of a matching box for a specific antenna, or a choke intended to stop reflected RF coming back into the radio. No other markings?

NOT A TA
NOT A TA UltraDork
9/7/21 6:38 p.m.

IIRC those were sold as a booster for antenna.

Hungary Bill (Forum Supporter)
Hungary Bill (Forum Supporter) GRM+ Memberand PowerDork
9/8/21 7:00 a.m.

Yeah, no other markings at all...

i was thinking it might be a filter of somesort but figured amplification was out of the question since there were no power wires going to it...

I guess i'll have to open her up and see what we can see laugh

Hungary Bill (Forum Supporter)
Hungary Bill (Forum Supporter) GRM+ Memberand PowerDork
9/8/21 7:01 a.m.
NOT A TA said:

IIRC those were sold as a booster for antenna.

Were those boosters legit, or more along the lines of snake oil?

paddygarcia
paddygarcia GRM+ Memberand Reader
9/8/21 9:46 a.m.

If there are no other wires to it and it's billed as a booster, definitely snake oil.

If you see coil-like things when you open it up, it's some sort of match box used to tune up the interface between transmitter and antenna.

It's possible that a match box would get more power out the antenna, so maybe they billed that as 'boosting'. But a good 1/4 wave antenna is already close to the 50 ohm impedence that your radio circuits want, so there is little or no benefit from matching.

Hungary Bill (Forum Supporter)
Hungary Bill (Forum Supporter) GRM+ Memberand PowerDork
9/8/21 11:08 p.m.

Awesome.  Sounds like it's headed for the bin.

 

Thanks everyone!

Cactus
Cactus HalfDork
9/8/21 11:43 p.m.

You could get an SWR meter, try it with and without the box, see if it makes a difference.

ShawnG
ShawnG UltimaDork
9/8/21 11:48 p.m.

CB radio is still a thing?

 

RacingComputers
RacingComputers GRM+ Memberand Reader
9/9/21 7:45 p.m.

10-4 Good Buddy

GeddesB
GeddesB GRM+ Memberand New Reader
9/9/21 9:45 p.m.

Bandpass Filter.  Only let's CB frequecies get to the radio.

Hungary Bill (Forum Supporter)
Hungary Bill (Forum Supporter) GRM+ Memberand PowerDork
9/10/21 11:44 a.m.
Cactus said:

You could get an SWR meter, try it with and without the box, see if it makes a difference.

That's what I was thinking.  I've been meaning to order one anyways, now is a good time.

Hungary Bill (Forum Supporter)
Hungary Bill (Forum Supporter) GRM+ Memberand PowerDork
9/10/21 11:45 a.m.
GeddesB said:

Bandpass Filter.  Only let's CB frequecies get to the radio.

Interesting!

That would explain why it was directional.

Kendall_Jones
Kendall_Jones Dork
9/10/21 12:50 p.m.
ShawnG said:

CB radio is still a thing?

 

I wonder - My motorhome has one of those "all in the handset" cobra radios.  Had it on all across the country one time and never heard another voice other than the marine / weather channel.

Truckers must be using an app on a tablet or something?

paddygarcia
paddygarcia GRM+ Memberand Reader
9/10/21 1:24 p.m.
GeddesB said:

Bandpass Filter.  Only let's CB frequecies get to the radio.

Good call. Could also be to keep a transmitter from interfering on other bands. TV at 54MHz would be interfered with by a crappy 27MHz transmitter (or a decent transmitter with a crappy amplifier).

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