CB Fire Stik Dipole Question

[Handy Andy]

Look at Mower Junkie's YouTube channel at the 102 SS whip dipole he recently made and put up on his house He
says it does very well and the DX gates doesn't lie

Found This too It's got some good stuff - makes it a little more complex - but, that is due to the structure he wants to mount it with

Thanks!

 

[Highway Man]

@Andy, I see you scrolled down. He has made a few antennas that has done some good Tube videos

 

[Highway Man]

My question is how would you tune this type of antenna. The firestik one

 

[M0GVZ]

Can you educate us on this?

I’ve noticed that for 1/4 cb antennas performance seems to drop sharply below 5’. 4’ is still plenty tolerable, but 5’ and up I’ve hardly been able to tell the difference with a full 1/4 wave (comparing RX signals on an S meter).

My question would be about the 25%. What does that mean and where does it come from??

OK so basically it's down to Radiation Resistance (Rr) which is the sum of the total power radiated by the antenna, divided by the square of net current causing the radiation.

Rr is a function of the electrical length (not the physical length), and how the current flows over that length. The longer the antenna's electrical length, the higher the Rr will be.

The rate of change is a square law function. So because of that a doubling of length gives an increase in Rr of 2 squared or 4 times where you started from. Reciprically halving the length results in a Rr of 1/2^2 which is 1/4 of the value or 25% of where you started from originally.

So...moving on to the S meter. They use dB which is logarithmic. An increase of 3dB is double, 6dB is four times, 9dB is eight times increase and 10dB a tenfold. A decrease of 3dB is a halving or 50% from the original value, a decrease of 6dB is a quarter or 25% of the original value.

So doubling the length of the antenna increases Rr by four times.Likewise halving the length of the antenna reduces it to 1/4 of the efficiency or 25%. As CBs and many ham radios up to S9 use 3 dB per S point then it means doubling the length sees you get 2 S point increase and halving the length sees you with a 2 S point decrease.

So back to the OP's dipole. If you were running 10W into a 9ft whip you'd have to put 40W into a 4ft Firestik to give the same received signal strength to the other end. But the same works for receive as well so unfortunately with the 4ft Firestik you'd be receiving them much weaker and are likely to not even hear a station that would be S3 or S4 on the 9ft antenna.

 

[Riverman]

OK so basically it's down to Radiation Resistance (Rr) which is the sum of the total power radiated by the antenna, divided by the square of net current causing the radiation.

Rr is a function of the electrical length (not the physical length), and how the current flows over that length. The longer the antenna's electrical length, the higher the Rr will be.

The rate of change is a square law function. So because of that a doubling of length gives an increase in Rr of 2 squared or 4 times where you started from. Reciprically halving the length results in a Rr of 1/2^2 which is 1/4 of the value or 25% of where you started from originally.

So...moving on to the S meter. They use dB which is logarithmic. An increase of 3dB is double, 6dB is four times, 9dB is eight times increase and 10dB a tenfold. A decrease of 3dB is a halving or 50% from the original value, a decrease of 6dB is a quarter or 25% of the original value.

So doubling the length of the antenna increases Rr by four times. Four times is 6dB. Likewise halving the length of the antenna reduces it to 1/4. As CBs and many ham radios up to S9 use 3 dB per S point then it means doubling the length sees you get 2 S point increase and halving the length sees you with a 2 S point decrease.

I recall much of that from studying for my license.
Two locals, unless they're close to one another, will definitely see that scenario played out on their meters. The good news is, as far as skip is concerned, when Mother Nature is smiling at you, a 4' Firestik dipole can/will work beautifully and the person on the other end will think you are pulling their leg when you tell them what you're using. Been there, done that.

 

[2NC995]

So doubling the length of the antenna increases Rr by four times. Four times is 6dB. Likewise halving the length of the antenna reduces it to 1/4. As CBs and many ham radios up to S9 use 3 dB per S point then it means doubling the length sees you get 2 S point increase and halving the length sees you with a 2 S point decrease.

I can’t refute the theory, certainly well over my head and why I asked you for a follow up.

I also realize the nature of the s unit, was just looking to quantify the 25% in a way that makes sense to the end user....and point out that 25% couldn’t mean 1/4 the s units.

Still, I haven’t ever been able to replicate any condition showing a loaded antenna 2 full s-units away from a whip. I imagine it would with a tiny antenna, but up around 4’ and more I can’t see it.

I haven’t played with the specific antennas mentioned...but my weakest performer, which is a Wilson 5000, shows only a fraction of a s-unit difference on the receiving end. Literally just a sliver of a needle’s difference, and you’ll go cross-eyed trying to see it.

I recall 25 or some years ago with one of my first setups I had a Hustler magnet mount. Probably 48” or so. I talked DX all over on that $20 antenna, and did quite a bit of local talk also. CB shop talked me into a Wilson and I hurried home and had a buddy some 15 miles away give me signal reports...zero difference. None. Of course, now I realize I just traded one base loaded antenna for another, but back then I was wondering where my dollars went on this supposedly magical antenna.

It’s mighty difficult, from what I can see, to show a single S unit increase with an antenna swap on a mobile.

Not to say I won’t take all I can get...I run the Texas riding around and use a full 1/4 when working DX.

 

[HomerBB]

I made one of these proposed dipoles once.
That was enough for me. The bandwidth was very narrow compared to a full length dipole.
The full length proved more fun to make for me.
Life is too difficult to to waste any increased measure of fun.
My preferred dipole for a band as easy to work with as 11m is two fiberglass fishing poles with wire on them joined in the center by PVC nipples and tee. Can be used horizontal or vertical easily.

 

[HomerBB]

Or, as mentioned, vertical sleeved dipole. Needed it above the Yagi.

 

[Handy Andy]

There is such a beauty in this thread. The consistent looks into the issue of making an antenna work - radiate - so others can hear you.

@M0GVZ - nice segue into a topic that not too many have touched on. Radiation Resistance, or "how to make your antenna Emit more radiation". Shorter antennas don't do this as well as the larger, longer or to read this as Elements with larger Surface areas to radiate signals from.

How can you tell?

Well it's simple physics as well as just common sense

Consider the ISOTROPIC - talk about quantum theory - look at the period at the end of sentence.

Even then, that "dot" is only representative of the theoretical

You can cover the dot. But the properties remain.

Think about the Dipole - 1/4 over 1/4 - a line into two segments - fed in the middle. One works the other.

Now you have a working element in space - you're occupying a volume - you have surface area in which to radiate a signal.

Compare it to a streetlight.

From a simple distance, you can cover the bright glare of the lamp with you hand. Maybe, just maybe - see the halo or reflection - glow of objects reflecting the light from that same source.

• When you're really close to it- you cannot truly remove the light from your view, even by closing your eyes, the eyelid is thin so the light can shine into and thru it as you see it still - only without shape or focus, just the light thru the layer casting a filtered light into your eye.

Just understand the concept of blocking the light and seeing it's ability to shine out to other objects - brightly enough to let your eyes see the objects being illuminated by the source your blocking. Again, a light is a form of electromagnetic radiation - you have a source which then radiates outward, only to be reflected-to illuminate the objects that block or cast a shadow behind themselves - eventually the light can no longer "illuminate" and provide enough reflection -energy to reach your eyes - it simply fades into a spot of light, if you walk away from it.

You can still see it, but as you gain distance away, the objects that come into the way of you from the light source, casting the shadow, are now placing you into that shadow of the cast light as well.

• If you make the light "bigger" by increasing the size but not its wattage or energy - you lose the brilliance but you use that energy to radiate from a larger surface.
• You can then take it's energy to spread across the surface area of the "diffuser" to even though you lose the "glare" you can still see light emission from that surface - which didn't exist if you only used point sources of light. The Shadows are not longer so contrasted against the night.

Same can be applied to the Radio - the Electromagnetic radiation spectrum still uses those same properties but now the waves or radiation can reflect or otherwise diffuse into the ambient level of radiation - you can then filter it out like you do with sunglasses - even polarized, to reduce the softening effects of the various angles in which the light arrives to you. IN fact - polarization of sunglasses are pretty much what you are doing with the antennas you use to both radiate and the reception of the same.

So - keep the conversation going - just wanted to make an observation (SIC)

 

[HomerBB]

@Handy Andy
My Grandpa used to stare at a candle through a glass of water in search of "Divine Simplicity"
Is that kinda the same thing?

 

[Riverman]

@Handy Andy
My Grandpa used to stare at a candle through a glass of water in search of "Divine Simplicity"
Is that kinda the same thing?

Just tried that and think I caught a glimpse of it! Albeit momentarily.

My Grandad, at ninety, used to stand in his old, dilapidated blacksmith shop behind his house staring around. I’m not sure he actually missed the work, but I know he missed being able to do it. He would have slapped old age around some had he gotten his hands on it.

 

[Handy Andy]

@Handy Andy
My Grandpa used to stare at a candle through a glass of water in search of "Divine Simplicity"
Is that kinda the same thing?

In light of, that I may burn in Hades; for even attempting to respond...

Er, Yes and No...

Yes, due to the obvious simplicity - many feel the "larger is better" tends to be the odds on favorite...

No, because the Glass in neither Half empty or Half full. Staring longlingly into the "ether" to seek Divine - is our innate nature of asking ourselves - "Why Did I even Bother To Respond To This Thread?" - but then to decide whether one is thirsty enough to Drink - only to remember that man cannot live on Bread alone. The Carbohydrates contained within can kill - but it would be a slow - if not tasty - death if you meet the right Baker.

No, this one is spelled with 2 "K"'s - OK?​

Ok, enough of the Metaphors...and all kidding aside...

When we look at antennas being what they are - radiators - you can see where "point sources" - although can be very bright - lack the ability to work around objects in either refraction or overall diameter of the light - it can easily be blocked by small innocuous objects you don't think of ever exerting any sort of influence.

I guess the idea (bulb in the head - now out on the lamppost) when you use a simple small bulb you only have so much surface area in which to work with. In the larger bulbs - those "envelopes" that contain the filament are larger as well - so they too can affect the radiative ability to refract and diffuse light from their internal sources.

But again - taking the perspective - this is with point lighting - even with a "frosted glass" or clear - the starkness of contrast in shadow is evident.

• The point I am making, is thru the observation of the more lengths of radiator you use, the ability of signal it can radiate efficiency becomes greater - as a form of working resistance to the "ether" of atmosphere or the region of space around it can be worked to provide an unrestricted or at least unmodified field of radiation "sphere of influence".

It's why we have gain values that seem to make some operators take off the gloves and start playing hockey - skipping the boxing match...

It is fortunate in the Radio spectrum, that is different - for by wavelengths we have the ability to pass thru barriers that would otherwise block light. So in properties alone, we have an ability to travel or move along and propagate thru, around and along objects, that other forms of radiation emission (READ higher energies) would not or have been so restricted, their losses would degrade it's ability to be discerned thru the background radiation it now seems to become a part of.

• Back to the Polarization, we have an ability to radiate as well as "capture" signals using similar polarization - which makes the enigma a paradigm shift of thinking on how to answer such questions without simply admiring the simplicity of the event - why explain it - or - even try to?

So as the physical antennas - as their lengths get shorter - their appearance to generate a "sphere of influence" is greatly altered or diminished when you look at the working ability of free air space comparing to the shorter less surface length elements. Losing the physical length - alters the ability to form a wave in the natural form or propagation - once the wave is formed or created - it moves away but the effort the antenna does to generate it, much of it is lost in the transmutation of the energy from electrical to radiative - losses are in heat - not necessarily in ohmic - or reactive - in fact we have less reactive even though the electrical properties are highly inductive of the loading, to offset the capacitive effects of the loss lengths in which to use the physical "length properties" but were forced to use smaller shorter elements using less surface area.

The propagation is not the problem - the physical versus the electrical conversion of the shorter - highly inductive elements - hinders the effectiveness. So the odds tend to favor the longer antennas even with the less Watt/M^2 per unit of length per physical lengths to natural electrical conversion properties - you have better odds of not having the signal blocked or losses incurred by the elements' inability to use the physical attributes of length to it's advantage.

 

[HomerBB]

I think you said that the bigger the antenna the better it is likely to radiate because it's bigger than the little antennas and bigger than the little things in the way and bigger than that schmuck 4 blocks away who has a teeny tiny little antenna and uses a lot of echo....
Right?

 

[Handy Andy]

Well, yes, theoretically...

Possibly even in the physical realm as well.

Of course!


Skip-zones aside, smaller (Read this as shorter radiators relative to ISOTROPIC) don't fare as well against 1/4 wave (dipoles) or above in length...

Resonance takes precedent over Impedance - Physical length in which to radiate (Resonance) fares better than the typical "loaded coil" lengths being shorter - even though their "Electrical properties" appear as longer wave antennas.

The physical aspect of the shorter radiators hinder or compromise their natural ability to form a field around them using the physical space for the field - hence the "Radiation Resistance" is much lower - there simply is less (area) to work with.

 

[2NC995]

Rr is a function of the electrical length (not the physical length), and how the current flows over that length. The longer the antenna's electrical length, the higher the Rr will be.

I'm still reading and trying to learn...now wondering if this is the nuance that causes the differing results I've seen.

Assessing a 4' firestick to be 25% of a 1/4 wave antenna would be based on it's physical length, not electrical...or am I missing something yet?