That whole coax length thing...

[Marconi]

eddie,
lou does not get everything correct in his books,
this was talked about on another forum, i have seen at least one error about coax electrical length,

when calculating phasing harnesses other than 1/Waves you must also have resonant antennas with the same characteristic impedance as the coax,
terminating coax with a pure resistance other than its own characteristic impedance causes reflections and those reflections cause an interference pattern of current and voltage between forward and reflected wave
( remember the double slit experiment )
current will lag or lead voltage as you move along the line dependant on the pure resistive termination been higher or lower than coax characteristic impedance and inverting at 1/4wave points, if the load also has reactance it causes further phase shift,


as far as i am aware ( always trying to learn ) the only time current or voltage delay is proportional to the calculated electrical length is when the line is terminated by a pure resistance of its own characteristic impedance or when the line is an electrical 1/2wave.

another instance i can think of where coax length has an effect is when the coaxial outer braid common mode impedance causes line radiation screwing up your radiation pattern,

is coaxial length important?, that depends on what you expect the coax to do.

Hey Bob, I tried the single split experiment before I consider the double spit idea, but on shining my flashlight thru the split, I didn't see them light particles stack up on the blackboard like they did in the video, so I figured trying two flashlights probably wouldn't work either. I do believe the other guys experimental results however.

When we were building co-phase harnesses back in the good ole' days we used 102" whips, sold them and the harness as a kit, and advertised on the package that the antennas were 50 ohm, so we met your high standards for performance. We just didn't know about all that other stuff you mentioned, but you are probably right. In the beginning, we used 98-100 ohm military surplus coax and after a while we found out that even though the harness worked very well, water got inside of the coax due to the coax construction. The center conductor was loose fitting in the dielectric and floated around inside. Based on this construction, I'm surprised the coax worked at all. There was a problem thought, cause when that coax was exposed to the outside elements, under a truck for example, water would get into the harness---even though we sealed the coax well at all points.

We tuned those harnesses by trimming the pigtail stubs until we saw a flat match, packaged them all up with a "distributed by Mike Craft CB Radio" label and off they went---back in the hay-day of CB radio.

 

[bob85]

lol, i have not tried it eddie but i read a fair bit about it,
its a well known unexplained by mainstream science experiment and well worth looking at for anybody under the illusion that science understands how things really work,

try two narrow slits

i like lou's books too, the understanding and repairing book is the best i have seen, what he said about coax was so cleary wrong i figured he can't have proof read it before it went to print,

i never knew you made phased antenna harnesses eddie, your a dark horse aint ya lol,
if the coax was sealed how do you figure water was finding its way in?.


jeff,
trying things out of the box lmao my saturns not been out of its box since i got it,

shut up mack.

 

[mackmobile43]

lol, i have not tried it eddie but i read a fair bit about it,
its a well known unexplained by mainstream science experiment and well worth looking at for anybody under the illusion that science understands how things really work,

try two narrow slits

i like lou's books too, the understanding and repairing book is the best i have seen, what he said about coax was so cleary wrong i figured he can't have proof read it before it went to print,

i never knew you made phased antenna harnesses eddie, your a dark horse aint ya lol,
if the coax was sealed how do you figure water was finding its way in?.


jeff,
trying things out of the box lmao my saturns not been out of its box since i got it,

shut up mack.

 

[Marconi]

lol, i have not tried it eddie but i read a fair bit about it, its a well known unexplained by mainstream science experiment and well worth looking at for anybody under the illusion that science understands how things really work, try two narrow slits

Bob, I think the reason I can't see the particles of light stack up on the blackboard is due to my old eyes.

i like lou's books too, the understanding and repairing book is the best i have seen, what he said about coax was so cleary wrong i figured he can't have proof read it before it went to print,

You would know about the repair stuff for sure. I didn't get his books for that very reason, I don't understand the circuit.

i never knew you made phased antenna harnesses eddie, your a dark horse aint ya lol, if the coax was sealed how do you figure water was finding its way in?.

Either there were holes in the seals, or condensation made the water inside. We used marine grade hot Bee's Wax to make the seals. The stuff I have is old and is double shielded with copper inside of silver solder copper outside. The dielectric is very thin PE and not foam. It is constructed like 9913 with a PE spline along the center conductor, but the spline is very small, it looks like it's straight and not curled around the center conductor. I think it must be curled though, to help keep the wire in the center.

The coax I have is RG71/u, and was made by Federal Cable for ITT. Belden makes this RF71u still, and it shows to be 93 ohms probably due to a thicker dielectric---which would really help with the water problem.

If I had a setup like we used back in the day, an all metal flatbed trailer to test on, I would build and tune one and see how it matched up with my analyzer. Since we tuned each harness after cutting close, the process took care of the VF, which I don't recall we knew what it was. We built only one kind and it was short, less than a E1/2 wavelength and was intended for the big rear bumpers on p/u trucks of the day.

I attach a picture, but I don't think you can see the details.

jeff, trying things out of the box lmao my saturns not been out of its box since i got it,

shut up mack.

 

[BOOTY MONSTER]

thanks old grandpa . ill be using 492 when im nerding out on trivial coax details .

and good to see you more active on the forum .

 

[bob85]

the only place i see 93ohm coax is cable tv eddie,
we had lots of it floating around when the cable guys were laying cable, this stuff was the size of rg213 but built like you describe,

booty,
492 is correct, don't be worrying about 468 x vf unless you are having a lou franklin moment, the clue is in the title of his well known book,
im sure eddie won't be losing sleep over it .





.

 

[loosecannon]

well, im glad we got that whole 492 vs 468 conundrum taken care of.

now its time to shake booty monster's world up again. LOL

what is the velocity factor of RG8x coax???

here is a quote from the venerable W8JI:


AK wrote:

Is 78% the correct velocity factor for RG8X coax?


NO.

RG-8X is really not an RG cable, and has no manufacturing standard.

Foamed cables can vary from near .7 vF all the way to near .9 vF

The manufacturer normally adjusts the ratio of air to dielectric to get
the correct impedance. Since RG8X has no standard dimensions or
conductor diameters, and it has no standard impedance range, the vF
will vary all over the place.

RG8X is normally a much denser foam (less air) than other foam cables.
The RG8X cable I have is in the low .7 range as measured on a network
analyzer. I've never found any with higher than the upper .7 range.

Since there is no manufacturing standard (meaning it is NOT really
suitable for an RG number) you should measure the cable.

73 Tom


so much for figuring things out to the "nth" degree. LOL
(sorry booty, just couldnt help myself! LOL)
LC

 

[Marconi]

loosecannon, when I test a segment off my spool of Belden's RG8x mini 8 with my Autek VA1, I consistently get .77 VF. When I test some SIW RG8x it varies like you note, but I don't see it going above .80 VF. The variation I see here, between the test value for VF and the spec, may well be an error in my meter.

I think this variations I see among different segments of the SIW is probably more common with this cheaper coax. I often see the cross sections in the SIW that are off center, where the position of the center conductor relative to the dielectric is skewed a bit and I have never seen the same with the Belden.

 

[BOOTY MONSTER]

well, im glad we got that whole 492 vs 468 conundrum taken care of.

now its time to shake booty monster's world up again. LOL

what is the velocity factor of RG8x coax???

here is a quote from the venerable W8JI:


AK wrote:

Is 78% the correct velocity factor for RG8X coax?


NO.


so much for figuring things out to the "nth" degree. LOL
(sorry booty, just couldnt help myself! LOL)
LC

LOL , i just try to do the best that i can given my budget and ability . many things are out of my control , but i try to do what i can as best as i can

 

[W5LZ]

The only time velocity factor is important is when you are dealing with timing/phasing, for whatever reason. 'Co-phasing' harnesses for dual antennas are far from the only reason for that timing/phasing. But, that's probably the most used application for most hams/CB 'ers.
Do some of that naughty word, 'math', and you'll see where that 93 ohm coax can come in very handy at times. It's been a very long time since I saw any, can't remember where I got it, seriously doubt if I'll ever have need for any more, but it is handy stuff at times.
- 'Doc

 

[loosecannon]

marconi,

looks like your results were right inline with what W8JI found.

booty, you know i was just trying to mess with you right? LOL

sometimes i just aint right!
LC

 

[BOOTY MONSTER]

dude i said LOL and even threw in a smiley
its all good , you get to live ...... this time

 

[loosecannon]

I'll get you banned from this board yet!
LC

 

[BOOTY MONSTER]

I'll get you banned from this board yet!
LC

ive been pretty good about doing that all by myself without any help from anyone else
maybe you could help speed up the process . i usually make too much sense so it takes me a while to get it done . i usually just get bored with the forum and give them no choice . but sometimes i get banned for calling the owner (cough 10 cough) and tell him hes too familar with a members ...... well ..... member (cough coolio cough) , or i try to start a thread that might cause a interesting discussion .

im such a horrible person !!!

 

[Carl]

bwahahahahha! i love it