CB Antenna help

[henryctx]

Hello,

My father in law has an older model Hy gain 5 element Long John that I think is 26 ft boom.

He says it is set for 10 meter from the factory and is looking for the correct specs to set it to 11 meter. I know very little bout RF, but I am assuming from this he is talking about the spacing of each of the sets of arials on the beam.

Also, he keeps mentioning something about needing an RF filter or choke inline with the coax just before the antenna connection. Can anyone point us inthe right direction?

Thanks for any help or suggestions. Also, his handle is "735 Texas - Antique" CB.

 

[2RT307]

I would contact Hy Gain Hy-Gain for the specifics. I think it just uses a ugly balun (choke), which is just winding up coils of your coax at a specific length and diameter. You can find that online as well, and I think here on the forum, too. Should make for one heck of an antenna!

73,
RT307

 

[henryctx]

Thanks for the information. I did contact Hy Gain, but they told me to search this message board or ask questions on here for specifics on getting the antenna set to 11 meters.

Also, they suggested some type of inline choke that is basically some sort of pigtail between your coax and antenna, but closer to the antenna end as opposed to the ferrite ring type rf choke.

Thanks for any ideas.

 

[Robb]

Yagi 5 element

 

[Marconi]

Hello,

My father in law has an older model Hy gain 5 element Long John that I think is 26 ft boom.

He says it is set for 10 meter from the factory and is looking for the correct specs to set it to 11 meter. I know very little bout RF, but I am assuming from this he is talking about the spacing of each of the sets of arials on the beam.

Also, he keeps mentioning something about needing an RF filter or choke inline with the coax just before the antenna connection. Can anyone point us inthe right direction?

Thanks for any help or suggestions. Also, his handle is "735 Texas - Antique" CB.

My experience with a LJ105CA there is not enough tubing material to reach CB. I could get down into 27.000 mhz, but the bandwidth was way to narrow.

You could try adding some longer elements in the end ends of the elements, but with the heavy swagged tubing the taper makes the measurements vary noticeably from any traditional measurements you might find.

Do you have a manual with your antenna? If not, try on www.CBTricks.com.

Good luck.

 

[2RT307]

Thanks for the information. I did contact Hy Gain, but they told me to search this message board or ask questions on here for specifics on getting the antenna set to 11 meters.

Also, they suggested some type of inline choke that is basically some sort of pigtail between your coax and antenna, but closer to the antenna end as opposed to the ferrite ring type rf choke.

Thanks for any ideas.

You might try Scott at Signal Engineering. He posted up the "Ultimate 11 meter DX antenna" a long time ago. I don't know if he modeled a 5 element or not, but his 4 element (Maco based) was quite a bit shorter boom wise than what Maco called for. Of course, it is centered around 27.555 for low SWR. Depending on your needs for 11 meters, you might be able to find something that works, despite the "short" boom length you have. Some of these guys have Eznec modeling software, and might be able to help you out as well. If you have a tuner (or want to buy one), you could make it work with the factory specs, but it won't be optimized for 11 meters.

73,
RT307

 

[2RT307]

On review, you can take a peek at the link Robb posted. Would probably work great!

73,
RT307

 

[KC9Q]

To get an understanding of what is required to change a 10 Meter antenna to an 11 Meter antenna use some math: This can explain a lot.

Basic formula: 468/F(MHz) is used to calculate the driven element (i.e., the element that is connected to the coax). The 468 formula is the standard ½ wave dipole formula. For 10 Meters one is likely to use 28.400 MHz for the design frequency (used for the lower part of the band for CW and SSB phone operation). For CB (11 Meters) the likely design frequency is 27.185 MHz (Channel 19 about in the middle of the band). Thus for 10 Meters the driven element is calculated as 468/28.400 = 16.478 ft = 16 ft, 5.75 in. For the CB band the driven element is 468/27.185 = 17.215 ft. = 17 ft, 2.6 in. You will need to lengthen the Driven Element 0.737 ft, or about 8.8”. That’s about 4.4” on each half of the dipole.

The Reflector Element is usually 5% longer than the Driven Element, so it should be about 17.215 x 1.05 = 18.075 ft = 18 ft, 1 in.

The first Director Element is about 5% shorter than the Driven Element or 17.215 x 0.95 = 16.354 ft = 16 ft, 4.25 in. The other directors are about 5% shorter than the previous director and so on.

So you can see that the antenna needs to be lengthened in general since the CB band has a longer wavelength than the 10 Meter band.

For the purist, the spacing, or distance between elements should be greater to maintain the same gain specs. However by leaving the spacing for the 10 Meter band the gain will decrease a small amount, so small that it isn’t worth the trouble.

Here is another site that explains yagi antenna designs, and provides further understanding.
http://signalengineering.com/ultimate/yagi.html

I hope this helps you some.

Mike

 

[Marconi]

To get an understanding of what is required to change a 10 Meter antenna to an 11 Meter antenna use some math: This can explain a lot.

Basic formula: 468/F(MHz) is used to calculate the driven element (i.e., the element that is connected to the coax). The 468 formula is the standard ½ wave dipole formula. For 10 Meters one is likely to use 28.400 MHz for the design frequency (used for the lower part of the band for CW and SSB phone operation). For CB (11 Meters) the likely design frequency is 27.185 MHz (Channel 19 about in the middle of the band). Thus for 10 Meters the driven element is calculated as 468/28.400 = 16.478 ft = 16 ft, 5.75 in. For the CB band the driven element is 468/27.185 = 17.215 ft. = 17 ft, 2.6 in. You will need to lengthen the Driven Element 0.737 ft, or about 8.8”. That’s about 4.4” on each half of the dipole.

The Reflector Element is usually 5% longer than the Driven Element, so it should be about 17.215 x 1.05 = 18.075 ft = 18 ft, 1 in.

The first Director Element is about 5% shorter than the Driven Element or 17.215 x 0.95 = 16.354 ft = 16 ft, 4.25 in. The other directors are about 5% shorter than the previous director and so on.

So you can see that the antenna needs to be lengthened in general since the CB band has a longer wavelength than the 10 Meter band.

For the purist, the spacing, or distance between elements should be greater to maintain the same gain specs. However by leaving the spacing for the 10 Meter band the gain will decrease a small amount, so small that it isn’t worth the trouble.

Here is another site that explains yagi antenna designs, and provides further understanding.
http://signalengineering.com/ultimate/yagi.html

I hope this helps you some.

Mike

Mike and henryctx, I'm not sure which beam model Henry has, but HyGain made several 10/11 meter models. My model is th LJ-105CA, 5 element, 10 meter Long John and is said to be setup and specifically tuned for all modes from 28.200 to 29.500 mhz with bandwidths ranging from 400 to 1100 khz for different modes. This should suggest that this antenna is very sensitive to individual settings within the very broad 10 meter band.

The problem with using the math or a calculator is...those procedures never consider the variables in the material length, per tapered element. You may end up close maybe, but such variables in material diameter do create errors that only modeling and then testing can calculate correctly.

Of course such errors can surely be adjusted-out to match and resonance during the tuning process...if you have the patience to do the work, and since you may have to tune the feed point trying to get a match on a modified multi-element antenna, you will have your work cut out for you, and you have no real guide lines on the resonance for all 5 elements. It will be like working from scratch.

Here is what Telex told me some years ago when I asked a similar question about the model I have.

View attachment HyGain LJ-105CA.pdf

The problem with this beam can develop due to not having enough tubing material for the tip elements and then trying to successfully modify all the settings. My beam came with an adjustable beta matching device, but several of the other 5 element beams HyGain made for 10/11 meters came with fixed beta matching devices, so they were not intended to be tunable at the match.

BTW, I was never able to get my beam to work as I expected in the CB band, and I used longer end tubing to reach resonance. The match was OK, but the performance was less that the preformance on my homemade 4 element horizontal yagi.

 

[W5LZ]

When retuning any antenna for a different band there's no 'formula' that will give the exact lengths to add/subtract. The answer from those formulas can't account for all the variables, but those formulas can certainly get you into the ball-park. Then, it's the same procedure for tuning -any- antenna, adjust things for best results. With that in mind it's usually best to start off slightly too long rather than too short. Why? Because it's typically easier to shorten something than stretch it. That's the definition of tuning an antenna and is absolutely 'normal'. It's also why manufacturers include a tuning method of some kind, you just can't account for all the variables between in different antenna mounting/placement situations.
Ever make an antenna and have it come out 'perfect' the first time? Then you are just very lucky.
- 'Doc

 

[henryctx]

Thanks to everyone for the help and information. I will get all of this to my father in law and see if he can make some sense of it all. RF is Greek to me, but I am learning as I am helping him along on his project.

Thanks! Henry

 

[Arkieguide]

Would he not be better off to take that one apart and maybe make a 3 element yagi out of the pieces.?