isolation from mast

[W5LZ]

You know none of this is frequency specific, it applies to all antennas no matter what band of use.
- 'Doc

 

[HiDef]

You know none of this is frequency specific, it applies to all antennas no matter what band of use.
- 'Doc

That's correct as long as everything is properly scaled. You cannot apply an antenna graph for a 40 meter dipole 40 feet above ground to an 11 meter vertical 40 feet above ground however.

 

[HiDef]

I will once I get the time

Put down that 807......

 

[mackmobile43]

Put down that 807......

what's an 807?

 

[bob85]

i can see what hi def is saying about wavelength vs height,
most people over here dont have their cb antenna up over one wavelength to feedpoint, they used to years ago, mine was up at two wavelengths in an open field but times have changed, neighburs attitudes have changed the local councils attitude has changed,


cebik had something to say on the issue of height above ground vs which lobe is the dominant lobe but did not commit,
he said it deserves more detailed investigation..

my feeling is that depending on the electrical length of the mast and the electrical length of the outside shield of the coax you will have lower or higher commonmode impedance, the worst case scenario been a mast or feedline that is electrically multiples of halfwaves between feedpoint and ground, best case been where that length is odd 1/4wave multiples,

i agree with hi def, unless your sleeve balun is made correctly with a very large sleeve to coax diameter ratio ( fat pipe thin coax ) and using low loss dielectric covering on the coax they wont have a high choking impedance at all, rg8 running through a 1" pipe is near useless.

 

[BOOTY MONSTER]

i was thinking what the article was saying about elevated ground planes and how elevated radials are better for an elevated antenna than ground planes/radials at earth or dirt level ..... would also apply to the whole mast system acting as a ground element . i understand that the frequency being TXed on will behave differently with their respective antennas . i certianly dont understand how that changes and exactly why , but i know it does .

still learning here

 

[delta]

i can see what hi def is saying about wavelength vs height,
most people over here dont have their cb antenna up over one wavelength to feedpoint, they used to years ago, mine was up at two wavelengths in an open field but times have changed, neighburs attitudes have changed the local councils attitude has changed,


cebik had something to say on the issue of height above ground vs which lobe is the dominant lobe but did not commit,
he said it deserves more detailed investigation..

my feeling is that depending on the electrical length of the mast and the electrical length of the outside shield of the coax you will have lower or higher commonmode impedance, the worst case scenario been a mast or feedline that is electrically multiples of halfwaves between feedpoint and ground, best case been where that length is odd 1/4wave multiples,

i agree with hi def, unless your sleeve balun is made correctly with a very large sleeve to coax diameter ratio ( fat pipe thin coax ) and using low loss dielectric covering on the coax they wont have a high choking impedance at all, rg8 running through a 1" pipe is near useless.[/


Bob what size form or sleeve would you recomend when using Rg 123 coax? Also does the form or sleeve have to be plastic or non conductive? I can get thin galvanised mild steel tube at almost any size from 5" to 50". Also how many turns on that particular size i ask this because someone said you could make a rf choke on the mast by winding it around the mast. I thought it shouldn't be touching the mast though, put me right if you would, please Bob.

 

[bob85]

delta,
i would not use a sleeve balun on a vertical if there was an easier method especially if you intend to use the antenna on a range of frequencies,

there is much more involved in constructing a none radiating sleeve balun with high choking impedance than running pvc jacket coax through any old piece of pipe,
if you manage to get it right it will only perform well over a narrow frequency range,

rg123?, if you mean rg213 i would use 6 turns on a 4-4.5" none rf conductive former or no former for 11mtrs, more turns as seen in the ugly balun on ham universe will give a lower choking impedance on 11mtrs,

i would never wrap a coaxial choke round a metalic mast.

 

[High Voltage Mobile NJ]

some of you guys still believe u have to use this method using wrapping the coax. in doing this you will create other problems if running power. u could possible resonate on other frequencies to. ive only made a rain loop on my antenna mast with just one turn about 8 to 10 inches wide to take the strain off the pl-259 connector going to the antenna . i have talked with some hams and was told , it does not make that much difference. if your antenna is grounded properly your interference should be very low.

ps. running power does not like resistance and small turns in coax, especially cheap coax.

hard line is the way to go baby !!!!!!!! :tongue:

 

[Shockwave]

some of you guys still believe u have to use this method using wrapping the coax. in doing this you will create other problems if running power. u could possible resonate on other frequencies to. ive only made a rain loop on my antenna mast with just one turn about 8 to 10 inches wide to take the strain off the pl-259 connector going to the antenna . i have talked with some hams and was told , it does not make that much difference. if your antenna is grounded properly your interference should be very low.

ps. running power does not like resistance and small turns in coax, especially cheap coax.

hard line is the way to go baby !!!!!!!! :tongue:

Well, that's not exactly right. If adding a coaxial balun alters the resonant frequency of your antenna, that is a sure sign that you needed the balun because the coax was radiating. RF traveling on the inside conductor of a coax cable is not effected by forming a coaxial balun since it is shielded. The coax shield will block the induction effect from reaching the center conductor when forming the coil. Only the outside braid experiences the choking action.

You mention a valid point about coiling high power cable because too sharp of a curve can cause the insulation to fail. Most quality cable will list the minimum bend radius of the particular cable in the specifications. Some antennas used at high power will benefit from the use of a coax choke to reduce feed line radiation.

The easiest way to see if you need a coax balun is to move your coax away from the mast at the base of the antenna. If you can see a change in VSWR as you move the coax away from the mast or towards the mast, it is radiating and a coax balun will help. Adding one in these cases will restore the antennas desired radiation pattern and reduce RFI. My means of testing will not spot all cases of radiating coax however, it's a great first indicator.

 

[jazzsinger]

some of you guys still believe u have to use this method using wrapping the coax. in doing this you will create other problems if running power. u could possible resonate on other frequencies to. ive only made a rain loop on my antenna mast with just one turn about 8 to 10 inches wide to take the strain off the pl-259 connector going to the antenna . i have talked with some hams and was told , it does not make that much difference. if your antenna is grounded properly your interference should be very low.

ps. running power does not like resistance and small turns in coax, especially cheap coax.

hard line is the way to go baby !!!!!!!! :tongue:

It came from hams so it must be "TRUE"

below is the dictionary definition of the word AMATEUR,I'd pay particular note to number 3 with the emphasis on the words unskilled and inexperienced, and also to the synomyn "NOVICE".Despite the fact many will baffle you with bull to convince you their amateur licence is actually a phd in rf engineering.


–noun 1. a person who engages in a study, sport, or other activity for pleasure rather than for financial benefit or professional reasons. Compare professional. 2. an athlete who has never competed for payment or for a monetary prize. 3. a person inexperienced or unskilled in a particular activity: Hunting lions is not for amateurs. 4. a person who admires something; devotee; fan: an amateur of the cinema.
–adjective 5. characteristic of or engaged in by an amateur; nonprofessional: an amateur painter; amateur tennis.

Origin:
1775–85; < F, MF < L amātor lover, equiv. to amā- (s. of amāre to love) + -tor -tor, replaced by F -teur (< L -tōr-, obl. s. of -tor); see -eur

Synonyms:
2. nonprofessional. 3. dilettante, tyro, novice.

 

[W5LZ]

No matter what the subject, it eventually turns into a CB'er -vs- ham thing. I think it's such a great thing, don't you?
- 'Doc

 

[HiDef]

No matter what the subject, it eventually turns into a CB'er -vs- ham thing. I think it's such a great thing, don't you?
- 'Doc

Anytime somebody has to throw off the focus of a discussion to a name calling event you know they feel defeated.

While we are calling people names I can say the scariest source of disinformation I've ever seen comes from people masquerading as broadcast engineers. BTW that's not directed at anyone here.

There really isn't much difference between hams and cbers anymore so why bother to bring it up.

 

[Moleculo]

Jazzsinger -

The Ham vs. CB thing is not welcome on this site and I don't think you've commented on a thread recently without attempting to start up that tired diatribe. The unique thing that most people appreciate about this site is that we can all talk radio without letting that age old "battle" creep into the discussion. Read the FAQ again in case you forgot what is in there.

 

[dudmuck]

some of you guys still believe u have to use this method using wrapping the coax. in doing this you will create other problems if running power. u could possible resonate on other frequencies to. ive only made a rain loop on my antenna mast with just one turn about 8 to 10 inches wide to take the strain off the pl-259 connector going to the antenna . i have talked with some hams and was told , it does not make that much difference. if your antenna is grounded properly your interference should be very low.

ps. running power does not like resistance and small turns in coax, especially cheap coax.

hard line is the way to go baby !!!!!!!! :tongue:

grounding actually has nothing to do with interference to the neighbors.
grounding can make it worse in some instances due to bringing the RF closer to the house.

You actually only need a DC ground of your antenna to the earth. The purpose is to provide lightening protection, or reduce static on the receive.

As far as "ugly" baluns go, otherwise called wrapping coax..
It blocks RF on the outside of the coax, but the DC path (to ground) is still there.
You need to be concerned with the number of turns to prevent self-resonance.
Too few turns and its not effective. Too many and it becomes self-resonant.
Bob85 had it right: rg213 i would use 6 turns on a 4-4.5" none rf conductive former or no former for 11mtrs
Perhaps up to 10 turns would be ok. It probably optimum for the ugly balun to be self-resonant at 4x your operating frequency, or in otherwords resonant at 1/4 wavelength.

hard line is a waste on 11 meters. Its for high power on UHF or VHF.