mobile coax help

[Captain Kilowatt]

All that velocity factor is absolutly unimportant for ANYTHING we do. Period. Didnt exist til rather recently, and is a buzzword to try and look important and sell expensive coax. I challenge anyone to show me where, in real world use, it makes a damn bit of difference. That is like figuring the velocity factor of light before buying light bulbs. You can, but why?
Coax length makes not one whit of difference in most applications, except in really long runs, or very high frequency, and that is only because of losses.:bdh:
Forget all that crap, use good quality 8x or 8u and have a great day.

Remind me to never invite you over to help me phase a set of beam antennas for VHF or a pair of verticals for HF. While we are at it remind me to never invite you over when I have to make up a conjugate match http://en.wikipedia.org/wiki/Impedance
to match an antenna to the cable.

 

[BOOTY MONSTER]

"As for rg8x,you will very rarely find that in the same sentence as good quality coax."

hey jazz ,what kind of difference could i tell im my tx and rx on 10/11 or 12 meters between 56 feet of 8x and 60 feet of davis bury-flex ? i run a little under 200 watts pep .

 

[W5LZ]

"Certainly is that simple if you only transmit on one channel,seeing as most cb'ers tend to transmit anywhere between 26 and 28 mhz these days,sort of complicates matters slightly,as resonance is only found at one frequency,which means there will be standing waves on the cable,and there will be x amount of impedance transformation going on of growing amounts the further you move either side of that resonant frequency and depending on what fraction of a wavelength/multiple thereof you cut that random cable too."
Ah, but if you change frequency enough to require retuning the antenna for that new frequency, you've run into the same thing that people have for the last 100 years (almost). You are trying/expecting something to work that isn't reasonable, as in one non-adjustable antenna to be even close to resonant over a wide range of frequencies. Makes me wonder about how 'good' an antenna is that has an SWR of "1:1" over '40 below' to '40 above', straight out'a the box. (Never heard that before, right?)
Can an antenna be made to work over that range of frequencies (or greater) without it being adjustable in some way? No. That would require a miracle and those seem to be in short supply. If someone claims they have such a thing, the only 'miracle' involved is in they're believing it.
The 'qualifier' with those "daylight to dark" antennas is that they are, and have to be, adjustable in either length or loading. Without that 'adjustability', it just ain't gonna happen. The only "antenna" I can think of that has a super wide 'resonance' range is a carbon 50 ohm resistor. Uh... ~IF~ you determine how 'well' an antenna is working using ~only~ SWR as a reference.
- 'Doc

 

[jazzsinger]

"Certainly is that simple if you only transmit on one channel,seeing as most cb'ers tend to transmit anywhere between 26 and 28 mhz these days,sort of complicates matters slightly,as resonance is only found at one frequency,which means there will be standing waves on the cable,and there will be x amount of impedance transformation going on of growing amounts the further you move either side of that resonant frequency and depending on what fraction of a wavelength/multiple thereof you cut that random cable too."


Ah, but if you change frequency enough to require retuning the antenna for that new frequency, you've run into the same thing that people have for the last 100 years (almost). You are trying/expecting something to work that isn't reasonable, as in one non-adjustable antenna to be even close to resonant over a wide range of frequencies. Makes me wonder about how 'good' an antenna is that has an SWR of "1:1" over '40 below' to '40 above', straight out'a the box. (Never heard that before, right?)
Can an antenna be made to work over that range of frequencies (or greater) without it being adjustable in some way? No. That would require a miracle and those seem to be in short supply. If someone claims they have such a thing, the only 'miracle' involved is in they're believing it.
The 'qualifier' with those "daylight to dark" antennas is that they are, and have to be, adjustable in either length or loading. Without that 'adjustability', it just ain't gonna happen. The only "antenna" I can think of that has a super wide 'resonance' range is a carbon 50 ohm resistor. Uh... ~IF~ you determine how 'well' an antenna is working using ~only~ SWR as a reference.
- 'Doc

It's not expecting something to work thats not reasonable,it's about being realistic on the effects of resonance and how far off resonance an antenna will perform before performance is seriously compromised.

An antenna straight out the box with 1.0:1 swr is generally known as a dummy load.I've certainly heard people claim that before,but people who get 1.0:1 swr readings across a wide bandwidth is indicictive of lossy coax as i mentioned previously,and they generally know nothing about antennas or transmission lines either.Once you redo their coax with decent quality coax you are guaranteed to see the traditional stretched u shape swr curve,even across 40ch's.

An antenna certainly will work across a range of frequencies,but again you have to be reasonable in your expectations and expect performance to drop off the further you move from resonance,all antennas should be tuneable,if they aren't they are useless,there is too many things can upset an antennas tuning for them not to be.

swr or to give it its full name,Voltage Standing Wave Ratio,is a poor indicator of antenna performance,you can have a very low VSWR yet still be miles away from resonance,as a VSWR meter can't distinguish reactance.The reality is though for some people its the only test equipment they can afford,and its better than nothing.The best way to tune any antenna is for maximum signal.There is many ways to match antenna impedance to transmission line/transmitter after maximum signal/resonance is found.Very few antennas are resonant at their lowest VSWR point,with the exception of the starduster / 1/4 wave ground plane with drooping radials,which is designed to be so.Most other antennas need matching circuits of one description or another.

Radio output circuits are designed to withstand a certain amount of mismatch indefinately,so perfect VSWR isn't all it's cracked up to be anyway.It's just another cb myth touted by people who are ignorant of facts,many commercial radio stations run KW's into 3.0:1 and greater VSWR's month after month with no problems,because there equipment is designed to handle it.

 

[jazzsinger]

"As for rg8x,you will very rarely find that in the same sentence as good quality coax."

hey jazz ,what kind of difference could i tell im my tx and rx on 10/11 or 12 meters between 56 feet of 8x and 60 feet of davis bury-flex ? i run a little under 200 watts pep .

I'm assuming by tx/rx difference your reffering to the S meter readings involved,if so you probably won't see any difference at all,but that is far from the whole story,

Quality coax isn't just about the difference in signal,far too many people are hung up on coax attenuation and overlook its other qualities/shortcomings,

Far more important is the rfi noise picked up by poorly shielded coax that masks very low signals,not to mention plays a huge part in leaking rfi to other electrical equipment around you,then there is the issue of the stability of better quality coax when used in adverse weather conditions,generally speaking foam dielectric cables like rg8x are only good for indoor use,for reasons i've already mentioned,the cables generally break down pretty quickly when exposed to moisture or ulta violet light.Davis buryflex advantage is in its jacket,which is designed to be buried under the ground,which can help with rfi suppression,but going by the price of it I doubt very much if its built from high quality materials.

With your 60 feet or so run there will be precious little difference between any rf cables in s meter readings,its too short for losses to play a noticeable part,1 s point is around 6db gain or loss,very few coax cables will have that amount of loss in 60ft apart from the really cheap bargain bucket cables,but there could be a huge difference in noise pickup/rfi radiated which is nothing to do with the length of the cable.S meter accuracy is another issue which can give over emphasised losses or gains,as most are nowhere near the 1 s unit= 6db mark they should be,that includes most hf sets too.So going by s meter is about as accurate as tuning an antena with a swr meter,much better to use the two best test instruments nature provided,your eyes and your ears.Both are very sensitive,the ears will hear increased/decreased noise levels and your eyes will see that neighbour who's telly your ripping apart coming with a shotgun long before the f@cker gets a chance to pop you,

If you really want to see increased performance (not just s meter readings),buy a quality coax,like M17/75 RG214/u with the dual silver plated braid,which is excellent hard wearing coax,with superb shielding.The biggest problem you'll run into with this cable is soldering the plugs,the conductors are of such quality that they will pull the tip temperature down on any iron under 60w,i use an antex tcs 230 (temperature compensated) when doing rg214/u,tinning the braid can be difficult,but its well worth the effort over rg8x type cables,and at the prices you guys get it at it ain't a ballbuster.

Always solder the braid to the plug,not only does it give a better electrical connection,but it gives a better mechanical connection too,and stops the wind twisting the cable and the inevitable broken inner conductor that results.seal up with liquid electrical tape and/or self amalgamating tape and you have a connection that will last as long as the cable itself,which in the case of proper M17/75 RG214/u is 20 years,if a job's worth doing,its worth doing properly the first time.

If your feeling really flush booty,consider the andrew heliax range of ldf cables,or not as good/expensive times microwave lmr range.Both may be considered slightly overkill for 11m though.

 

[W5LZ]

jazzsinger - !! Exactly !!
- 'Doc

 

[BOOTY MONSTER]

I'm assuming by tx/rx difference your reffering to the S meter readings involved,if so you probably won't see any difference at all,but that is far from the whole story,

Quality coax isn't just about the difference in signal,far too many people are hung up on coax attenuation and overlook its other qualities/shortcomings,

Far more important is the rfi noise picked up by poorly shielded coax that masks very low signals,not to mention plays a huge part in leaking rfi to other electrical equipment around you,then there is the issue of the stability of better quality coax when used in adverse weather conditions,generally speaking foam dielectric cables like rg8x are only good for indoor use,for reasons i've already mentioned,the cables generally break down pretty quickly when exposed to moisture or ulta violet light.Davis buryflex advantage is in its jacket,which is designed to be buried under the ground,which can help with rfi suppression,but going by the price of it I doubt very much if its built from high quality materials.

With your 60 feet or so run there will be precious little difference between any rf cables in s meter readings,its too short for losses to play a noticeable part,1 s point is around 6db gain or loss,very few coax cables will have that amount of loss in 60ft apart from the really cheap bargain bucket cables,but there could be a huge difference in noise pickup/rfi radiated which is nothing to do with the length of the cable.S meter accuracy is another issue which can give over emphasised losses or gains,as most are nowhere near the 1 s unit= 6db mark they should be,that includes most hf sets too.So going by s meter is about as accurate as tuning an antena with a swr meter,much better to use the two best test instruments nature provided,your eyes and your ears.Both are very sensitive,the ears will hear increased/decreased noise levels and your eyes will see that neighbour who's telly your ripping apart coming with a shotgun long before the f@cker gets a chance to pop you,

If you really want to see increased performance (not just s meter readings),buy a quality coax,like M17/75 RG214/u with the dual silver plated braid,which is excellent hard wearing coax,with superb shielding.The biggest problem you'll run into with this cable is soldering the plugs,the conductors are of such quality that they will pull the tip temperature down on any iron under 60w,i use an antex tcs 230 (temperature compensated) when doing rg214/u,tinning the braid can be difficult,but its well worth the effort over rg8x type cables,and at the prices you guys get it at it ain't a ballbuster.

Always solder the braid to the plug,not only does it give a better electrical connection,but it gives a better mechanical connection too,and stops the wind twisting the cable and the inevitable broken inner conductor that results.seal up with liquid electrical tape and/or self amalgamating tape and you have a connection that will last as long as the cable itself,which in the case of proper M17/75 RG214/u is 20 years,if a job's worth doing,its worth doing properly the first time.

If your feeling really flush booty,consider the andrew heliax range of ldf cables,or not as good/expensive times microwave lmr range.Both may be considered slightly overkill for 11m though.

thanks for the elaborate reply jazz . im not a needle watcher , except for when im comparing/changing something . like you said i go by what im hearing on my end and how successful i am at making the far off local or skip contact . its always nice to get replies that youre breaking their needle what ever , but being herd and also hearing them it the goal . ive also learned that meters arnt accurate so that another reason i dont watch them . they are only useful when compared to itself IMO and what my ears and my contact success tells me is much much more important .

i knew the gain loss and power handling for my short run would be negligable , but the ability to keep noise out of my coax and keep my coax from affecting nearby electronics is a difference i could hear every day . the only problem ive had with the 5/8 befor when using the 8x coax was my laser mouse on my computer flashing with my modulation when using extra power . when i had the wire starduster id have to unplug and reconnect the mouse half the time , so the 5/8 had muck less interference coming off of it . i used the same coax on each so it was the antennas making the difference , le were mounted in the same location with the 1/4w feedpoint being about 3 foot higher than the 5/8 was .

whats your opinion on the browning coax that sparkys has ?

Browning BR-400 Super Premium Low Loss Coax 50'

im not believing its better than the LMR-400 but im really on a budget . the buryflex will cost me $51 plus $5 processing and about $11 shipping ....WITHOUT THE 259's . they want $10 for each one if they put them on .

i can get a similar length of the browning from sparkys for less than $60 with ends already attached and about $10 shipping . i was planning tp just get a new 56 foot section or 8x from sparky since i hadnt had an problems (that i noticed or was aware of) with the 50 foot section i got from him befor . his 8x is made by belden .

what i dont like about the browning is the solid center conductor . id prefer a stranded center because its more flexable and easier to work with . and the heliax is definately out of the question $$$.

 

[jazzsinger]

To be honest Booty its a cable I've never come across here in the uk,the claims made on it sound a bit iffy at the price it sells for though,I doubt very much if its on a par with times microwave lmr 400.I personally would avoid the solid centre conductor type cables,i prefer multistrand centre conductors,buryflex may well be a better buy for the money your willing to spend.

As for claims browning manufactures the best low loss coax in the world,i'm sure Andrew the company that manufactures heliax and many others might beg to differ on that one,I smell cb bullshit.


As for $10 dollars to put a plug on,hmmm,something you should really be doing yourself,as A) its the only way to be sure its done right,B) its the only way to be sure quality plugs are used.

Sounds like your starduster was giving common mode curent on the shield,as its pretty much a balanced antenna it should be choked.

 

[mackmobile43]

I will install all the pl-259's you want for $10 a pop.