Steve Saunders Goldwing Forums banner

Status
Not open for further replies.
1 - 13 of 13 Posts

·
Premium Member
Joined
·
303 Posts
Discussion Starter #1
imported post

Hello all,

I amlooking for someone in North San Diego, CA area that has the equipment and knowledge to tune my 97SE :18white:CB Antenna.

I have a very old SWR meter and no connecting cables. :(

Any idea what this might cost to have done?

Thanks in advance for the advice

Rick
 

·
Premium Member
Joined
·
626 Posts
imported post

You need the connecting cables with the Motorola connectors at one end anyway. The Honda CB's always come with that silly antenna connection.
 

·
Premium Member
Joined
·
2,381 Posts
imported post

If you have an old SWR meter it should be pretty easy. Go to radio shack and buy a length of 50-ohm coax with PL-259 connectors already installed.

Now take the SWR meter and connect the coax you just bought to the 'Transmitter' side of the meter. Disconnect the antenna cable from the radio and connect it to the 'Antenna' side of the meter. Plug the other end of the newcoax into the radio. You should now have the SWR meter connected between the radio and the antenna. Depending on what Honda uses on their radios, you might also need some adapters.

There's probably a switch in the front of the SWR meter that says'Forward' and'Reverse'or 'SWR' or something similar. Set the switch to the 'Forward' or 'Calibrate' setting. There should also be a knob on the meter - set the knob to the lowest setting. There might also be a switch for low power and high power - switch to the lowest setting... lowest wattage (a CB only puts out about 4 watts).

Now tune the radio to the bottom of the band and key the mic (don't key the mic for more than 10 seconds or so). While keying the mic turn the knob on the SWR meter until the needle registers the highest on the scale - don't peg the needle, carefully bring it up to the highest mark on the meter, or as close to it as you can get. Unkey the mic and again, don't key for more than about 10 seconds at a time.

Now switch the meter to the 'Reverse' or 'SWR' setting and key the mic again. The needle should not move as much as before. The meter scale probably has marks on it for SWR that read something like 1:1, 1.5:1, 2:1, 3:1 and so on. You want the meter to read less than 2:1 while transmitting.Record the reading you got at the bottom (lowest frequency) of the band.

Go to the top of the band (highest frequency) and do the same and record the SWR.

Do the same in the middle of the band.

If the SWR is below 2:1 across the band, you're good to go. If not, then its a simple matter of adjusting the length of the antenna until the SWR is below 2:1.

The bottom of the band has the lowest frequency and the top of the band has the highest frequency. Since frequency is inversly proportional to wavelength, antenna length is also inversly proportional to the frequency... higher frequency, shorter antenna - lower frequency, longer antenna.

By playing around with the length of the antenna you'll be able to get the SWR down to where you want it. Remember that if the SWR is too high at the bottom of the band and is lower at the top of the band, you'll need to lengthen the antenna - shorten if it's the other way around.

If the SWR is far higher than about 3 or 4 to 1, then you might have a loose connection or the antenna is just way out of adjustment or defective.

Optimally, if you know which channel you'll be using the most, you should strive for less than about a 1.5:1 SWR for that channel.

Play with it and you'll get the hang of it.
 

·
Premium Member
Joined
·
303 Posts
Discussion Starter #4
imported post

Thanks everyone for the info.

I am OK with the procedures, I'll go buy the cables which isn't a problem. The problem I have is the SWR meter I borrowed is so old, the features don't match up with all the information I have received.

Attached is the meter I have.

I don't know the exact setup, the meter doesn't seem to show the same markings that are mentioned.

Thanks again for all the help

Rick
 

Attachments

·
Premium Member
Joined
·
2,381 Posts
imported post

Do you have a better picture of the meter. Your attached picture is too small to see the markings for the switches and knobs.
 

·
Premium Member
Joined
·
303 Posts
Discussion Starter #6
imported post

Hello all,

OK, I broke down and bought a Radio Shack meter and cables.

Antenna all the way down, I am getting 1.38 on Channel 1 and 2.5 on Channel 40

Antenna all the way up, I am getting 1.41 on Channel 1 and 3+ on Chanel 40

Is this saying that the antenna is still to long even when all the way down?

Thanks, Rick
 

·
Premium Member
Joined
·
2,381 Posts
imported post

Your antenna is probably designed to operate as a 1/4-wave antenna when its all the way down and a 1/2-wave antenna when its all the way up. It all has to do with the resonance of the antenna. I'm assuming that this is a telescoping antenna.

I'm not really sure what antenna you have, but if there is an adjustment for permanently shortening the antenna by the use of a set screw or something similar, try to shorten it about 1/4-inch at a time until the SWR goes down below 2:1 on channel 40. Then check it again on channel 1. If you don't know what channel you'll be using most of the time, I'd aim for the lowest SWR on channel 19 or 20.

Don't operate the radio with the antenna anywhere between full up or full down because it will not be resonant (high SWR) at those in-between lengths, and it will overheat, or at least reduce the life of,the transmitter.
 

·
Premium Member
Joined
·
303 Posts
Discussion Starter #8
imported post

Marco,

The antennafolds downwhenthe cover goes on, it's up when riding, it's not a telescoping antenna. It is a 2 piece antenna. The top section moves up and down approx 1" and held in place by 2 set screws.

If the antenna is all the way down and gives me 1.38 on Channel 1 and 2.5 on Channel 40, doesn't that mean the antenn top is still too long?

Iam hesitant to measure 2 and cut once andhave it still too short :)

Rick
 

·
Premium Member
Joined
·
2,381 Posts
imported post

toy4rick wrote:
Marco,

The antennafolds downwhenthe cover goes on, it's up when riding, it's not a telescoping antenna. It is a 2 piece antenna. The top section moves up and down approx 1" and held in place by 2 set screws.

If the antenna is all the way down and gives me 1.38 on Channel 1 and 2.5 on Channel 40, doesn't that mean the antenn top is still too long?

Iam hesitant to measure 2 and cut once andhave it still too short :)

Rick
Okay... sounds like the antenna can be folded down, not pushed down to a shorter length. Ihope I understand now.When you say all the way down, do you mean folded stowed for storage?

Anyway, you should do your measurements with the antenna in the position itwould be when you are riding the bike and operating the radio - preferrably away from any large metal objects(other than your bike) that can interact with the antenna.

Yes, if the antenna has a high SWR at the upper end of the band (highest frequency) and low SWR at the bottom of the band (lowest frequency), the antenna must be shortened. As I said before, frequency is inversely proportional to antenna length.

Most antennas have a set screw or other device that holds the upper portion of the whip (I think you said yours has this). This set screw(s) can be loosened and the upper whip can be slid down into the lower part of the antenna. If it doesn't have this, or if there isn't a similar arrangement toward the bottom of the antenna, as a last resort you might have to cut off a small portion of the whip. Be absolutely sure that your readings are correct and only lower or cut off a very small portion of the antenna at a time... it's very hard to add it back!

If the upper whip bottoms out inside the antenna you might have to take it out and cut a small portion off at the bottom of the whip.
 

·
Premium Member
Joined
·
303 Posts
Discussion Starter #10
imported post

Marco,

I have only taken readings with the antenna in the riding position, not in the folded downstorage poistion.

Mine does have the top section that slides down into the bottom section about 1" and is held in place with set screws. When I say up and down, I mean this 1" distance for the top section.

I have already taken off about 1/4" in 2 steps and the readings don't seem to be changing. I am concerned that taking off 1/8" then another 1/8" didn't seem to help.

Is the top section still way to long tothe change I have so far?

Thanks, Rick
 

·
Premium Member
Joined
·
2,381 Posts
imported post

There is probably not going tobe much of a change with 1/4" removed. I'd keep going a little bit at a time.

You've already said that the SWR is higher when the whip section is all the way up... so shorter is the way to go. In the end it might take more than an inch or so.
 

·
Premium Member
Joined
·
16 Posts
imported post

If Marco's advice doesn't pan out, it could be because of a lack of groundplane on the bike. 1.3 or 1.4 is good for being on a bike. The VSWR will be at a minimum at resonance, and will go up either side of it. For instance, if you normally operate at Channel 20, the VSWR should be MINIMUM at that point, and rise as you go in either direction (to channel 1 or channel 40) However, being that you are probably dealing with a center loaded coil (seems to be mostly) there are losses in the coil, not to mention the lack of a proper ground plane which will preclude you from achieving a perfect conjugate match (VSWR of 1). Tune the CB to favor your part or channel that you will be operating on the most. These new CB's have transistorized outputs and as such, will throttle back on their output power as VSWR increases, thereby DECREASING the likelyhood of blowing any final transistors,(It's a self-protective thing).

Also, the coil in most of these CB's are there to counteract the capacitive nature of 'Short Antennas'. The wavelength of the CB Band (aka, in HAM Radio Terms, The 11 Meter Band) has a wavelength of approx. 36 ft. There is no way to put a quarter wave antenna (8 ft) on a bike, hence the circular coil inside the antenna to compensate for the capacitive reactance of the 'shortened antenna'. You can imagine what a HALF Wave (16 ft) antenna would look like on a bike....lol.

Just tune it for MINIMUM on your favorite part of the band (channel) and have fun. 1.3 or 1.5 is good for what we have.
And by the way, about the only way to achieve a perfect 1:1 match would be with a gigantic, perfectly matched antenna or a dummy load. :cool:
 

·
Premium Member
Joined
·
2,381 Posts
imported post

N9FRP wrote:
If Marco's advice doesn't pan out, it could be because of a lack of groundplane on the bike. 1.3 or 1.4 is good for being on a bike. The VSWR will be at a minimum at resonance, and will go up either side of it. For instance, if you normally operate at Channel 20, the VSWR should be MINIMUM at that point, and rise as you go in either direction (to channel 1 or channel 40) However, being that you are probably dealing with a center loaded coil (seems to be mostly) there are losses in the coil, not to mention the lack of a proper ground plane which will preclude you from achieving a perfect conjugate match (VSWR of 1). Tune the CB to favor your part or channel that you will be operating on the most. These new CB's have transistorized outputs and as such, will throttle back on their output power as VSWR increases, thereby DECREASING the likelyhood of blowing any final transistors,(It's a self-protective thing).

Also, the coil in most of these CB's are there to counteract the capacitive nature of 'Short Antennas'. The wavelength of the CB Band (aka, in HAM Radio Terms, The 11 Meter Band) has a wavelength of approx. 36 ft. There is no way to put a quarter wave antenna (8 ft) on a bike, hence the circular coil inside the antenna to compensate for the capacitive reactance of the 'shortened antenna'. You can imagine what a HALF Wave (16 ft) antenna would look like on a bike....lol.

Just tune it for MINIMUM on your favorite part of the band (channel) and have fun. 1.3 or 1.5 is good for what we have.
And by the way, about the only way to achieve a perfect 1:1 match would be with a gigantic, perfectly matched antenna or a dummy load. :cool:
Yep... that's why I told him anything below 2:1 is good enough. My ham call is W7WIK, but haven't been on the air lately due to being back in school full-time. Most of my operating is CW when I do get on the air... sometimes do some digitalstuff using RTTY, PSK31, and Pactor. Rarely do I talk into a microphone except for local FM stuff.
 
1 - 13 of 13 Posts
Status
Not open for further replies.
Top