Have a look here for mobile install tips www.k0bg.com Keep in mind its the metal under the antenna not alongside that counts.
-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
Need Coax advice for mobile antenna
- Thread starter jr26
- Start date
I have read through most of http://www.k0bg.com/ it doesn't sound like stake hole mount is Ideal. Tying to figure out if its worth the time and money to move to the stake hole or leave it on the box. I know roof is best but I really don't want to drill a hole in the roof or put a 102" that high. The 102" on the box is mounted on the driver side in about 6" from the bed rail and the feed pint is about 2' above the bed floor the box is aluminum.
Mine works fine on my tool box…
I would leave it on the box, remember its the metal UNDER the antenna that matters the most.
i have for 25 plus years have a gull wing tool box with a antenna mount in the center, a hustler c 32 ball converted to a so239 a amphenol 90 degree into rg213 9 feet long to my amp and from amp to radio a 6 foot rg8x works for me swr is 1.3 or better from 26.5 to 27.70 the antenna is a antenna specialist 102 inch whip i bought in the late 1970s and the 6 inch spring is a military heavy duty i bought at a government auction, the whip dont lay down at highway speeds and it takes the shock of hitting things,,
Last edited:
It is a good coax but remember, it is a foam dielectric type coax. Watch out for sharp bends. Center can migrate to the shield and that is not good. That is why a solid dielectric coax is more suitable for mobile. RG-400 would have been the best choice. It is freaking expensive, but worth the price.
oh lord, you had to open that can of worms. here we go
Oh boy... This is a topic that has been known to cause many... heated discussions... yea, I'll leave it at that.
The one and only correct length for coax in an antenna setup is the length it needs to get from the antenna to the radio. I will generally add an extra foot or two to make accessing it easier should I ever need to in the future.
There are people that will insist that an electrical 1/2 wavelength of coax is the correct length, and there are many that drop the electrical part, insisting that 18 feet is the only correct length. Both of these lengths have some advantages and uses, but those really have nothing to do with the typical mobile (or really any) installation, short of in some cases essentially only hiding the snake that is biting at your ankles.
An electrical half wavelength, namely, near a physical 18 feet (on CB band) multiplied by the velocity factor of the coax (typically between .66 and .85 depending on the type and brand of coax) is beneficial only when you are using something more advanced than an SWR meter to tune your antenna. This measurement is good for one and only one frequency, and does not apply to the entire CB band (like a lot in the hobby try and use it for). So if the electrical half wavelength of coax is tuned for CB channel 20, The measurements for every other channel will be a bit off. If you are using an SWR meter (or jsut the SWR of return loss reading on a more advanced piece of equipment), again, this coax length is pointless.
NOTE: In addition to what I wrote above, many newer devices that are more advanced than an SWR meter don't have this limitation, and can actually calibrate out the effects of the coax, so this length of coax is even less relevant now than it used to be.
A physical half wavelength of coax has the tendency to hide certain antenna problems. Your SWR may look good, but while transmitting you are still blowing transistors and getting RF shocks through the mike or other parts of the radio. This is amplified when running more power. The cause of this is, instead of fixing a problem you are only hiding it from being easily noticed. You might get lucky and not see any residual issues, but you might also have several reoccurring problems that are hard to explain and track down.
An older thing people used to do with coax is, some people noticed that changing the length of the coax would appear to change the antenna's SWR, and they would try and tune antennas based on this. When changing the length of coax changes an antenna's SWR, this is a sign that you have a problem, and like the physical half wavelength I talked about in the paragraph above, you tend to have hard to track down problems when doing this. As a matter of fact, I recommend getting a barrel connector and an extra three foot length of coax, and plug it when tuning the antenna, if this changes the SWR noticeably, or it goes up at all, then you have said problem and should ask about it.
The DB
No it doesn’t. But sometimes, the could be Common Mode Currents and cable length movies might affect readings.
The best way to tune an antenna ( mobile or base ) is to use an antenna analizer with a 1/2 wave jumper. This article explains itself
