Wire Lengths

In your post, the comments about short grounding cables have much

merit.

However, the use of TUNED lengths of cables between equipment appears to

be VERY IMPORTANT. Dr Bare specifies 1/2 wave or 18ft cables in his

construction plans.

It appears that frequency tuned lengths of cables are required to avoid

suppresion of harmonics of the fundemental frequencies which essential

to plasma effect . This process is not well understood at this time.

In my pesonal experience, my equipment operated "electronicaly" fine

using short cables, but I found that I did not "feel" the ray beam

effect, EXCEPT WHEN USING TUNED CABLES. I have used full wave, 3/4

wave and half wave connecting cables with success.

It is my opinion that it also may be effective to use smaller fractions,

(such as 1/4, 1/8, 1/16, 1/32, 1/64 th wave) if properly tuned, however

I have not tried this yet. (and tuning becomes much more critical as

you approach a smaller fraction of full wave). Please refer to my

previous posts on cable lengths and math involved. Also errors in

calculating the velocity factor in the wire become significant.

In summary I strongly recomend that until further data is obtained, that

1/2 wave or 18ft cables be used to connect cb to linear and linear to

the antenna tuning device. These are commonly availible from cb radio

sources.

---------------------------

I had it backwards when I stated the length to be increased vs

decreased. I have been using way-off lengths to match wavelength since

I have been using 95%, which is incorrect since looking in catalogs

informs that the propagation velocity is usually around 70%, not

90-95%

For a 70% cable, then, the following chart would be relevant

(rounded to the nearest half inch.)

27.125 MHz

Ft (0.70)xWL (ft) ft, in

1/1 36.276 22.59 22, 7

1/2 18.13 12.69 12, 8

1/4 9.07 6.35 6, 4

1/8 4.53 3.17 3, 2

1/16 2.27 1.59 1, 7

1/32 1.134 0.79 0, 9.5

---------------------------

From: Domenic Spinale

Subject: Re: Propagation Velocity

A while back there was some talk on the List about the use of exact

sub-multiples of 1/4 wavelength transmission lines; and back then I did not

have time to get in my two cents worth.

When a lossless transmission line is terminated in its characteristic

impedance, the voltage measured at all points along the line will be the

same and the line is said to be flat which means the SWR is 1:1. The

opposite extreme is when the transmission line is either open or short

circuited which results in 100% of the signal that went down the line to be

reflected back up the line. The 27 MHz signal from the B/R system is

essentially a sine wave and the reflected signal is also a sine wave. With

two signals going in opposite directions on the same transmission line at

the same time, they algebraically add. The summation of the two waves is

called a standing wave. The highest voltage that can occur is at the point

where the peaks of the two waves are both at maximum with the same polarity

which results in twice the signal voltage. The other extreme is the point

where the two waves are exactly opposite in both polarity and amplitude and

they add to zero. The SWR is the maximum voltage point divided by the

minimum voltage point. When the two waves are of equal amplitude, the SWR

is 2 divided by zero which is infinity. These points of maximum voltage and

minimum voltage repeat every half wave length. A wave length can also be

expressed in degrees. A full wave length would be 360 degrees, similarly a

half wave length would be 180 degrees, and 1/4 wave length would be 90

degrees. Now recalling the sine function from trigonometry, it is zero at

zero degrees and increases in value to its maximum positive value of one at

90 degrees where it reverses direction then passes through zero at 180

degrees, continues in a negative direction to its maximum negative value of

-1 at 270 degrees where it changes in a posit ave direction, and passes

through zero at 360 degrees which is the same as zero degrees. The purpose

of this explanation is to show that the sine wave has a value of zero every

180 degrees (at 0 and 180 degrees) which is every half wave length. Maximum

amplitude points occur at 90 and 270 degrees, 180 degrees apart, also a

half wave length, but displaced from the zero points by 90 degrees or 1/4

wave length.

In conclusion it can be shown that a unique point (a zero or a maximum)

occurs every 90 degrees or 1/4 wave length.

If anyone would like to explain what is critical about 1/8, 1/16, or 1/32

of a wave length, I am all ears.

Domenic

===

===

>> In conclusion it can be shown that a unique point (a zero or a maximum)

>> occurs every 90 degrees or 1/4 wave length.

>>

>> If anyone would like to explain what is critical about 1/8, 1/16, or 1/32

>> of a wave length, I am all ears.

---------------------------------------------------------------------------

>Please explain the implications of this. Does it mean that the best

>size RF cables in this system are (ignoring prop velocity) are 9 ft and

>27 ft (approx 1/4 and 1/4+1/2 wavelengths)?

>

>If so, is there no ideal size if the cables are significantly less than

>these values? If there is no ideal size, then would cables in the,

>say, 1-6 ft range be "shorter the better" (least antenna action)

>or "longer the better (since they would be closer to 9')"?

---------------------------------------------------------------------------

I've been pondering the answer to the above question for a very long time

because sometimes things are not what they appear to be. I currently

believe that the coax cable length is not critical and shorter is better.

When I initially read that the recommended cable length between the CB and

the linear amplifier, as well as between the linear amplifier and the

antenna tuner was 18 feet, I thought: That's a half wave length - except

someone forgot to correct for the velocity factor of the cable. The 18 foot

length of coax is not a half wave length in the signal path, so scratch

that idea.

Another time I thought: Due to the load, the tube and its coupling back to

the tuner, being unbalanced resulted in a ground current flowing through

all of the ground connections; and since there is a voltage null every half

wave length and the velocity factor being closer to one for current along

the braid of the coax, that explains the recommended 18 foot lengths. This

scheme would hold the case of CB, linear amplifier, and antenna tuner close

to the same RF voltage potential. Then the recommendation is to coil the

coaxial cables. This adds series inductance in the ground current path and

defeats the 1/2 wave length grounding scheme. To correct this poor

grounding system, the recommendation is to connect all the equipment

together with short braided wire.

Thus far, I cannot find a good reason to support the idea of using 18 foot

coaxial cables. Provided that the SWR's are reasonably low there is no

magic length of coaxial cable. If the coaxial cables are short, the braided

wire ground connections should not be needed.

With respect to any imbalance in load current resulting in ground current,

it would make sense to null out the ground current at the balun with some

type of gimmick capacitor between the ground connection on the balun and

one of the balanced output wires. Nulling out ground current can solve

three problems. First, minimize RF interference. Second, minimize any

instability in the function generator caused by RF ground current. And

third, minimize any effect on the SWR when touching any of the equipment.

Other opinions are welcome.

Domenic

===

Subject: Re: Propagation Velocity

> I currently

> believe that the coax cable length is not critical and shorter is better.

That is what I have found, empirically, as far as the cable length

itself is concerned. However, using different sized cables can

seemingly affect SWR and power since one size may remove or cause

interference due to proximity with other equipment in the setup. In

the system I am building now shorter is always better so far (this is

where the tuner and balun sit on a shelf above the amp and CB.) In my

other system, where the balun, amp, CB, and tuner are all on the same

shelf, and the amp is 2" from the balun, using a long enough amp to tuner

coax to go around the balun rather than under or over it results in

better SWR and power.

> Thus far, I cannot find a good reason to support the idea of using 18 foot

> coaxial cables.

Bare states in the manual that it helps the tube light easier. It does

not seem to help in my system.

> If the coaxial cables are short, the braided

> wire ground connections should not be needed.

I have also found this as a result of experimentation. I do have one

ground (7") between the CB and freq generator since it

helps keep 120Hz focused for some reason, but grounding all the

equipment together makes it slightly worse.

=====================

I'm using a cheb type tube (He + phanatron type electrodes) and found that

12 gauge rope laid monster speaker wire in thick vinyl jacket of 26" + spade

type connectors works best for me....

The spade connectors are 10-12 ga. crimped on the ends of the wires, and

then silver soldered.... The identical setup w/ flat 1/4" tinned grounding

strap has SWR's of at least .25 to .5 higher (at differant frequencies...

With the spade connectors, the whole cable(s) tip to tip is about 27"

long....

On the cheb tube, there are screw connectors on the ends of the tube that go

to the internal electrodes...

I have not tried an argon tube yet but am saving my pennies for a quartz

bubble tube w/ Argon ir a mix as the Helium seems to work too good...

By that I mean I seem to have created a major kill off of whatever is in me

and was quite toxic for several days including a SVT reaction... and a

blowup (swelling and opening) of a lymph node in my groin.... I wasn't even

supposed to be the patient.... <grin>

It has spooked me however, and the person I was going to use it for, I won't

because of side effects for the moment.... anyways.... I don't want to

cause more pain where there is plenty to begin with.... Need to figure a way

to reduce the tumor in situ w/o more pain....

Hope this helps

Peter

GFoye wrote:

> I am not electronics oriented so this may not be good advice but:

>

> There are two thoughts on tube wire length.

>

> * One is: short as possible.

>

> * Other: wire length to fractional wave lengths.

> Therefore, for 1/4 wave, wire should be about 26" to 30" inches.

> Mine seems to work best about 26 to 28 inches - both equal length.

>

> Any technical input here?

>

> GF

====================

>[snip] I am using 14.5 feet of 9913F coax ( this is the

correct length, not 18 Feet as described by Jim.). The equation

for calculating ½ wave length must take into account the

velocity factor of the coax which can range for 0.66 to 0.84 (

0.80 in my case).

Rick and List:

It would appear that the above comments are based upon the

assumption that the signal path of interest is the RF power out

of the CB and going through the coax to the linear amplifier,

and/or the RF power coming out of the linear and going through

the coax to the tuner. Suppose the signal current of interest

was the result of the unbalanced current on the lines out of

the balun, and that current flows along the ground path. If

the objective was to hold the CB, the linear, and the tuner at

the same RF potential then 1/2 wave length connections between

them would make sense. When the current path is along the

outer conductor of the coax rather than the center conductor

with the outer conductor being the return path, the velocity

factor as expressed above does not apply.

Domenic

======================

I ran a quick, basic test on length of wire from balun to

tube. I believe a quarter wave would be about 28 1/2 "

length. (Don't know formula - got the figure from someone

else.) Just wanted to see what would take place with

varying wire length.

For this test I used the following: #10 solid wire,

attached to balun terminal with copper post connector

CP-4-2B Adamax Inc 495-875 purchased at Home depot. This

terminal made it very easy to remove wire, snip off a piece

and reinsert wire- tighten with a set screw.

Equipment:

Uniden 510XL modified per manual

palomar 225

MFJ 949E tuner with external balun connected with 24" coax

Lodestar AG2603AD

argon bubble tube

#10 wire: (two pieces)- made a coil by forming over broom

handle, slip fit for my tube at large diameter. Just insert

tube into the coils -must be sure coils are aligned properly

so there is no stress on tube. Started with 30" overall.

(Before coil, etc.). Snipped off 1/2" at a time.

(Will have to do this one more time to pin point exact

length for my set up. Think I passed it around 29 ". Also,

my tube started acting up, may have damaged it.) What I

found was: the optimum is going to be close to the

calculated figure of 28 1/2"

As length was shortened the SWR's climbed but not

significantly although at a couple points the SWR's did make

a huge jumps. (This is one reason the test would have to be

done about three times to see if this condition would

repeat.)

The significant change was in wattage reduction as length

was decreased.

At optimum (palomar on med) the wattage output was 200 with

reflected close to one.

As wire length was reduced wattage output dropped, lowest

about 150 and reflected about four. (Except at two

intervals where there were significant jumps: SWR 3:1,

watts 110.)

At a couple points I had to change from inductor L to K.

But, not sure what was happening there- would have to do

this again for repeatablity.

I went down to 26" and saw the wattage dropping steadily.

At that point I snipped off a 6" segment down to 20".

Wattage still low but not much different than at 26".

Results: in order to obtain maximum wattage output with

lowest reflected SWR, wire length is important. (So, for

those that build the compact units, how do you get around

this? Somehow you have to fool the system or do you use

long wire?)

I'm not a person with patience so I went through this

rather crudely. But, am going to do it again, starting with

30" and snip off 1/4" at a time and record results then

utilize the optimum figure.

Note: I believe the coils work nicely and could be used

similarly as the copper sleeves. Make a coil and solder

something else to it if you prefer.

GF

=================

Below is a link to a web site that has some interesting information on
coax cables.

http://members.tripod.com/~cb_antennas/coax_basics.html

Regards, Jason

=================

A note to the group about velocity factors. The output of an R/B is quite

wide band and is not merely fixed at 27.125 MHz. 27.125 Mhz is merely the

center frequency. The primary Lower Side Band (LSB) has harmonics that

extend about 3 MHz below the center frequency.The primary Upper side band

(USB) has harmonics that extend about 3 Mhz above the center frequency .

Most of these harmonics are 40 to 50 Db down, but they still do exist.

Calculation, and then fabrication of cable length based upon velocity

factor and a fixed 27.125 Mhz will result in poor SWR's. There are other

harmonic signals that are generated that extend out to a good 300 to 500

MHz. Again these are very weak. Some harmonics can be picked up below 10

MHz. An optimum coax cable should be able to contain all these harmonics.

The recommended 18' length of coax between the transmitter and the tuner

works just fine. Someone might try and have a 21' length made up to see

what happens to SWR. Might better contain the LSB frequencies.

Jim Bare

==============