Stealth Receive Only Antenna for 11M

[KC8WJG]

I'm going to be doing some interstate traveling in the next month and have a spare CB that I'd like to put in the car for receive purposes only.

Any suggestions for an antenna that I could either buy or build that could be kept inside the car?

How well would a quarter-wave length of coax work if I draped it around the back seat up by the window?

I know that the receive range would be very limited, but I'd like to be able to hear chatter within maybe a half mile or so. I just don't want another antenna on top of the car since I already have my 2m VHF 5/8 wave antenna on the roof.

 

[mmckenna]

Wire inside the vehicle is going to suck. Might be good enough for 1/2 mile of RX, but remember that most CB users are running really crappy antenna setups to begin with.

I'd suggest biting the bullet and putting a second mag mount antenna up.
Or,
if it really is receive only and you're going to pull the microphone so I don't accidentally transmit, T off the AM/FM radio antenna. While not resonate at CB frequencies, it'll work better than anything inside the car.

 

[prcguy]

Buy this and use your AM/FM car antenna.

GOLD LINE MULTI BAND ANTENNA COUPLER AM FM CAR AM FM CAR ANTENNA HAM CB SCANNER | eBay

GOLD LINE MULTI BAND ANTENNA COUPLER ALLOWS YOU TO MONITOUR 20-70 MHZ, 148-175MHZ, 250-470 MHZ WITH YOU AM/FM CAR RADIO ANTRNNA OR ANY ANTENA YOU HAVE UP. SHOW ROOM FIRST ASILE HALFWAY DOWN RIGHT SIDE.SECOND SHELF BLUE CONTAINER.

www.ebay.com

 

[KC8WJG]

Wire inside the vehicle is going to suck. Might be good enough for 1/2 mile of RX, but remember that most CB users are running really crappy antenna setups to begin with.

I'd suggest biting the bullet and putting a second mag mount antenna up.
Or,
if it really is receive only and you're going to pull the microphone so I don't accidentally transmit, T off the AM/FM radio antenna. While not resonate at CB frequencies, it'll work better than anything inside the car.

Well, that's kind of the whole point. I don't want to put another mag mount antenna on. That's just a another one that I have to pull off and stash when we park for the night. And sharing the AM/FM is not an option either. It was 25 years ago when car radios were the DIN type, but I wouldn't want to attempt it now on a 2022 model.

 

[ladn]

It's not going to work very well, but a CB "rubber duckie" antenna with an SMA or BNC mount in the rear window might give you what you want.
CB frequencies require a relatively long antenna for any sort of efficiency and caging it inside a vehicle just compounds the problem.

In reality, you'll have much better range with the two previously suggested external antenna options.

 

[mmckenna]

Well, that's kind of the whole point. I don't want to put another mag mount antenna on. That's just a another one that I have to pull off and stash when we park for the night. And sharing the AM/FM is not an option either. It was 25 years ago when car radios were the DIN type, but I wouldn't want to attempt it now on a 2022 model.

Well, let us look at this from a technical standpoint, then.
CB radio uses a wavelength around 11 meters.
How well do you think an 11 meter signal is going to penetrate a metal vehicle with windows much smaller than that? Reduce performance further for the noise sources inside the car, deep tint windows, defroster wires in rear/side windows?

Sounds like your idea is to toss a random length of coax in the vehicle somewhere and hope that it gets you enough signal to hear. It's not going to work well, even if you stripped the outer shield back 108" and made a quarter wave sleeve antenna, you are still trying to use an antenna inside a metal box. No idea what kind of car you are driving, so wouldn't want to guess. Maybe giving us some more info would get you more detailed answers?

If removing one mag mount for your ham radio is easy, but removing a second one for CB is difficult, I'm not understanding what the limitation is. But, it's your car, your antenna, you decide.

@ladn has a good idea about the small antenna in the rear window. Might work, might not, easy to try out.

Since you already have a 5/8th's wave VHF antenna on the roof, why not try a diplexer and see how that works. At least you'd have something vertical, outside the car, and with some semblance of a ground plane.

Comet Antennas CF-530 Comet Duplexers | DX Engineering

Free Shipping - Comet Duplexers with qualifying orders of $99. Shop Duplexers and Triplexers at DX Engineering.

www.dxengineering.com

 

[G7RUX]

I have been down this route before and an antenna inside the vehicle is going to be awful.
Options you have if you really don't want to use a magmount are:
1. use a manual AMU and tune up the rear screen defroster but I would recommend checking your tuner has series capacitance
2. use an active e-field antenna taped inside a suitable window...it's not going to be great but much better than 2.5 m of wire dangling around inside the vehicle
3. try using a window orifice as a slot antenna, although this will require access to nearby metal
4. if the vehicle has a sunroof then you could trail a 5m length of wire out of the sunroof with a small 'chute on the end to lift it. I have operated 40m CW mobile like this before and (a) it works and (b) is sketchy.

None of these will be even close to good (although I have had success with the window slot method) and will all be vastly outperformed by using a mini-magmount scanner antenna on the outside of the vehicle.

 

[prcguy]

Speaking of a slot antenna, in the mid 70s two companies made a tuning box with wire that stretched across a vehicle window making the window a slot antenna for 27MHz and the entire skin of the car became the antenna. I installed and tested quite a few of these in the 70s and they actually worked ok and better than some antennas of the day like 2ft long rain gutter clamp antennas. There are several on eBay right now and this one is very reasonable. This one is from the original company who invented it.

The Intenna Invisible Cb Mobile Antenna | eBay

I have been down this route before and an antenna inside the vehicle is going to be awful.
Options you have if you really don't want to use a magmount are:
1. use a manual AMU and tune up the rear screen defroster but I would recommend checking your tuner has series capacitance
2. use an active e-field antenna taped inside a suitable window...it's not going to be great but much better than 2.5 m of wire dangling around inside the vehicle
3. try using a window orifice as a slot antenna, although this will require access to nearby metal
4. if the vehicle has a sunroof then you could trail a 5m length of wire out of the sunroof with a small 'chute on the end to lift it. I have operated 40m CW mobile like this before and (a) it works and (b) is sketchy.

None of these will be even close to good (although I have had success with the window slot method) and will all be vastly outperformed by using a mini-magmount scanner antenna on the outside of the vehicle.

 

[krokus]

Since you already have a 5/8th's wave VHF antenna on the roof, why not try a diplexer and see how that works. At least you'd have something vertical, outside the car, and with some semblance of a ground plane.

Comet Antennas CF-530 Comet Duplexers | DX Engineering

Free Shipping - Comet Duplexers with qualifying orders of $99. Shop Duplexers and Triplexers at DX Engineering.

www.dxengineering.com

As I am rather late to this party, I am glad someone beat me to suggesting this.

To the OP: there are other models of these devices, from Comet and Diamond, so take a look at their websites.

Speaking of a slot antenna, in the mid 70s two companies made a tuning box with wire that stretched across a vehicle window making the window a slot antenna for 27MHz and the entire skin of the car became the antenna. I installed and tested quite a few of these in the 70s and they actually worked ok and better than some antennas of the day like 2ft long rain gutter clamp antennas. There are several on eBay right now and this one is very reasonable. This one is from the original company who invented it.

I haven't seen one of those in a long time. Thanks for that flashback.

 

[slowmover]

Speaking of a slot antenna, in the mid 70s two companies made a tuning box with wire that stretched across a vehicle window making the window a slot antenna for 27MHz and the entire skin of the car became the antenna. I installed and tested quite a few of these in the 70s and they actually worked ok and better than some antennas of the day like 2ft long rain gutter clamp antennas. There are several on eBay right now and this one is very reasonable. This one is from the original company who invented it.

The Intenna Invisible Cb Mobile Antenna | eBay

Intenna
The Invisible Ear Mobile CB Antenna
Model #3355
MICROWAVE FILTER COMPANY



Earlier RR thread:
The "InTenna" covert CB antenna by Microwave Filter Co. The unboxing

“For technical advice CALL THE INVENTORS and ask for Mr Tuner!”

.

 

[slowmover]

Disquise CB antenna needed for Ford Taurus or similar

Surprised at performance report.