Tip & How-To about Radio Communications

How to Build: Antenna Tuners

Get you a metal box about 4 inches X 4 inches. Use 2 female Cb antenna inputs from old Cb radios or Radio Shack. Get a old Am radio tuner out of a AM radio(530-1700 khz.) Buy or scrap up some copper wire; big gauge I used. Wound 8-10 turns about " 1 inch round close tight wound. Solder to AM tuner- C1 it shall say on top of Am tuner. Solder Center of Am tuner to Ground(Metal box). For those who know electronics the Tuner is 0-365pf Am band 530-1700khz types. OK, back to assembly. drill a hole for the Two Female Cb Inputs on both sides of metal box. Attach copper wire inside to center taps of Inputs on both sides. Drill a hole for Am tuner and Screw on its lock nut and place a knob on it. Solder all grounds of Female Antenna inputs and Tuner Ground and all Grounds to metal box. Use a washer and Bolt to lock down Grounds to Box. This is how it operates after you use a Jumper to hook to TX of Cb radio. Antenna to other side. Its just a simple L/C network. The Tx travels through copper wire(coil) inside box and gets shunted to ground by the right level of PF Capacitance. The operator tunes it in to get a close to 1.1 to 1.5 SWR ratio. Its simple, but helps with bad Antennas.

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I have spotty reception on a handheld CB and was wondering if there is a testing procedure I can use to check the antenna and radio. I have a multimeter. It's a radio shack handheld with weather bands and the antenna is a "rubber ducky" type

The antenna is your problem not much gain. Height is everything tx and rx. Although it would not compare to a conventional cb size negates performance. Seeing is believing in this case hearing get adapter to connect to standard coax of antenna. (PL259) to BNC Coax Adapter Radio Shack sells them. And dont ask or buy any radios there. They are hardly the radioshack of choice anymore.

  • If you put 4 watts into a four-foot antenna, you will get the same power out of that antenna as if you were putting 2 watts into a 102-inch whip.
  • If you put 4 watts into a 3-foot antenna you will get the same power out as if you were putting about 1.5 watts into a 102-inch whip.
  • If you put 4 watts into a 7.5 inch antenna on a hand held CB, it would put out as much power as a third of a watt into a 102-whip.
  • If you put 4 watts into a 102-inch whip antenna, it is the same output as if you put 11 watts into a 3-foot whip.
  • If you put 4 watts into a 102-inch whip antenna,, it is the same as if you put 14 watts into a 28-inch antenna.
  • If you put 4 watts into a 102-inch whip antenna, it is the same as if you put 54 watts into a 7.5 antenna.

May 21, 2011 | Cobra HH 38 WX 40-Channels Handheld CB...

1 Answer

i have lots of motor noise. when i unplug antenna it stops

The motor noise comes through power wires and antenna pickup. Get an old ferrite bar out of an old junk AM radio. That black bar with wire wound on it inside AM/FM radios. Tape it to your Antenna coax or try to add 2 of them. Just tape them to the coax at about 6" inches from your radio. Try to add a power wire filter to the RED(+) 12 volt wire and Black wire(-) to your radio. A power filter is just a Ferrite bead or small bar with about 10 wounds of wire and a 470uf capacitor from (+) to ground(black -). Make sure polarity on capacitor is wired (+)(-) that way too. Radio Shack has a "Power" line noise filter kit, that hooks up under your dash. Ask Radio Shack personnel about this they will help you locate a "noise filter" for noisy alternators.Its simple, also, your radio is doing a fine job if it picks up that sensitive through the antenna. That just shows you your antenna is doing a good job. I had a problem like that --I only talked on my CB with the ignition turned off though, it made since to park and talk.

Apr 21, 2011 | Cobra 29 LTD CB Radio

1 Answer

I have a Midland 1001Z 40-Channels Base CB Radio and a Magnetic-mount CB antenna. 29" stainless steel whip and 6" spring. About 46" high overall. All bought from /www.thesource.ca in Alberta canada. I hooked up a SWR meter to it to match them up. The end problem i had was when i was adjusting the antenna to get it at 2 or below. I cant get it to come down from 3. Not sure what I should do from this point. Can i cut down the antenna or replace it ? should i change it to a single antenna that is a Heavy-duty dual trucker kit with 1.2m (4') 1/4" wave helically-wound antenna, 20-gauge copper wire, factory-tuned ?

Try Grounding it better. Its supposed to equal 8.5 ft.(102 inches) but the coil may make that in all.You can clip like 1/8 inch off at time until it goes 2.1 Swr. Thats a good standard. 1.5 SWR is desired. If it don't have a coil with it that may be the problem. You could turn it into a 8.5 ft. antenna by buying a 102" inch whip to screw into the base of your antenna, it depends if it holds or not. You could build you a matcher like this with a solder gun+solder and 2 resistors. Get you a box with 2 female cb antenna inputs. Drill a hole for both Cb antenna inputs into box. Place them into holes screw nuts down snug. Run a copper wire inside to both grounds or a plate somewhat. Run a thick gauge copper wire from center cb ANT INPUT(2) to other input of ANT INPUT(1). Solder 2 100 ohms in parallel from input to Ground. If you could take apart your radio(eliminating the box idea). Just Solder 2 (100 ohm) resistors to your Antenna output then put it back together. 50 OHM MATCH HERE Is the main idea. I've used 75 OHM Tv coax and reduced SWR.

Apr 04, 2011 | Midland 1001Z 40-Channels Base CB Radio

2 Answers

tunning the antenna on radio shack cb trc-447

After installing the antenna, follow these steps to adjust the
standing wave ratio(SWR).
1. Turn on the CB.
2. Set S/RF/SWR/CAL to CAL.
3. Key the Mic and rotate SWR CAL so the meter points
to CAL.
4. Unkey Mic.
5. Set S/RF/SWR/CAL to SWR.
6. Key Mic again and note the actual measurement on
the SWR scale. Refer to the following table to interpret
the reading.

1:1 - 1.5 Great
1.5 - 2:1 OK
2:1 - 3:1 Not So Good
Higher than 3.1:1 Terrible

The ideal standing wave ratio (SWR) is 1:1, or a meter
reading of 1 on the SWR meter's top scale. A SWR ratio
of 1.5:1 to 2:1 is excellent for most mobile CB antenna

Check the SWR on Channel 1 and Channel 40
If the SWR is higher on 1, make the antenna longer
If the SWR is higher on 40, make the antenna shorter
Most antenna's are adjustable. Make small adjustments at a time.

Oct 10, 2009 | Radio Shack TRC-447 CB Radio

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