Can't get SWR right

[Aviator]

Just recently I put the radio outta my truck in the house hooked to a powersupply......I bought some antenna mast from ratshack and threw my 102"SS whip on there temporarily and can't get my SWR right for nothin. I'm using RG8U coax across the board even with my jumper for my PDC600LP meter.I cannot for the life of me get my SWR down at all....I know the whip isn't the best for a base station but I need it to get my fix until I can order a base antenna. I'm also looking for a decent base NGP antenna for my setup....I know I know, A99 or Imax 2000 but I need something a little less pricey since money isn't all that great right now and a little inconspicuos...Thanks guys.

[Slim Pickins]

Did you add any ground radials to that 102? Could be the mast is not creating enough of a counterpoise. I would think if the mast was the same length as the 102 it would act like a dipole, but then you would want the coax at a 90 degree angle to the antenna instead of running down the mast. You can buy ground radial hubs that whips will thread into from Texxcomm. You could also just add a few wires to the mount and tie them down on an angle or out flat.

I am sure some of the antenna gurus will chime in here but this is just my observations of what works from experimenting.

73s
Paul

[231]

Why not simply make your whip work? Try running some 8-1/2' wire radials off of the masting/mount set up you have (at least a few of them). The antenna itself needs to be insulated from grounding just like a mobile. But you still need a counterpoise. Without it you'll never get the standing wave down. My guess is right now you don't have that. If that's true, the radials will act as counterpoise as well as help with the radiation pattern some. Shouldn't be hard to install, just tie them off at a 45º angle like guy wires.

Perhaps another option is to make a wire dipole. There are tons of threads on them here and not only is the cost near nothing, but it works quite well. Half the fun is actually building one and making it work. If you want plug and play and it work well, then cough up the cash for an A99/Imax. You'll be disappointed in the performance of a NGP. Even your whip (configured correctly) is likely to out perform it.

Good luck.

[Red Warrior]

There are always two halves to an antenna. The 102 is only one half. The mast or the coax will be acting as the other half replacing the body of your vehicle that usually plays this role. The mast/coax is called acounterpoise and it's length must be calculated into the overall antenna length or the SWR will never come down.

Best to buy an antenna designed for this application which the 102 isn't.

[Aviator]

Yea sorry, my feed point is 15 up in the air.....I have a piece of 10 gauge wire attached to the mount that is approximately 9 foot long hanging straight down with 2holes punched in the lid of a plastic bottle and the bottle full of water...not sure if that's covered under the ground radial section but it MIGHT help...still doing nothin for SWR unfortunately....is this a correct example of a piece of a radial?Or is myconfiguration allwrong?Thanks for the responses....

[Red Warrior]

First of all, 102" is not resonant on 11-meters. 108" is the resonant length. If you have an ohmmeter check the resistance between the center of the coax and the shield of the coax while connected to your antenna. If it is zero, you have shorted the mount and you need to rework it. Make the antenna 108" long by adding copper wire to the end. Make your counterpoise 108" long and you should be in the ballpark.

[Aviator]

So, the coax doesn't need to be hooked to the radio in order to check the resistance? Thanks Red Warrior.

[Red Warrior]

So, the coax doesn't need to be hooked to the radio in order to check the resistance? Thanks Red Warrior.

Just to the antenna. You disconnect from the radio and check at the coax. That checks both the coax and the connection at the antenna.

[Aviator]

Any range of numbers to expect?

[Red Warrior]

Any range of numbers to expect?

The SO259 which makes up the mount for your 102" has no resistive connectivity between the antenna and the ground. Therefore you should measure a high resistance (basically an open) when using an ohmmeter..

[Aviator]

Alrighty thank you.....Now, if I attach radials to this thing made of 10ga wire will that be ok? Also, will they need to be tethered off or can they just hang from the mount down the length of the shaft loosely? Tryin to google this and getting mixed thoughts looking at ground radial pics.

[Red Warrior]

You should use at least 4 radials (preferably 90 degrees from each other) and their length is not critical. The angle downward should not exceed 45 degrees. If you are trying for stealth and cannot put 4 at 45 degrees, then use only a single 108 inch piece of copper wire connected to the ground side of the feed and hanging straight down without touching any metal (this is a counterpoise). No children should be able to touch this wire because even at low wattages, significant voltages can be felt in this wire.

[Aviator]

Alright, I am going for stealth and do have one hanging straight down..not touching anymetal.......I'll doublecheck the length of it if it stop raining before dark and adjust as necessary...any suggestions on attaching copper wire to the end of my whip to lengthen it? I just wanna say ya'll have been a big help and extremely patient with me and it's very much appreciated.

['Doc]

If a 'radial' hangs straight down you then have a 1/2 wave vertical dipole. They work too.
The angle of that/those radials with the vertical part of the antenna, determines the input impedance. The less the angle between radial and vertical part, the lower the input impedance, which with a vertical dipole is around 70 ohms give or take a few. Something around 45 degrees of angle, give or take a few degrees or so, ought to get you close to 50 ohms. That angle thingy is variable according to where the antenna is, what it's near, it's height, and so on. Don't worry if it's not 45 degrees, whatever works best is the best angle to have them on your antenna.
Antenna length and resonance.
A 102" whip is too short by just a little bit. A 108" whip is going to be too long by just a little bit. If you want a good ball-park length to work from, try dividing 234 by the frequency in Mhz. That'll give you an answer in feet. It's typically just a tad too long, but that's better than being a tad too short. That 108" will put you at the bottom end of the band. The 102" will put you at the top of the band. That method of finding a resonant length has been around for a very long time and is pretty accurate.
- 'Doc

[Red Warrior]

I took a stiff piece of copper wire and soldered it to an alligator clip and clipped it on the end of the whip. That worked on my mobile for several years.

[Red Warrior]

The reason the 102 is too short is they are designed to be mounted on a 6" spring.

[Aviator]

Last night...around 3am, I got a lil wild hair and check my coax(antenna hooked) with an ohm meter. Antenna connected, it read .4; Ithen disconnected the coax from the antenna and checked it once again (just to verify the coax was good) and it came up with an open circuit. it was suggested I pull the coax off the antenna once again today and read the resistance in the antenna. I'lldo that when I become more conscious this morning. Would a powdercoating on the mast cause lack of grounding for the mount? I wouldn't think so since it's electrically applied, but who knows.

[Red Warrior]

Last night...around 3am, I got a lil wild hair and check my coax(antenna hooked) with an ohm meter. Antenna connected, it read .4; Ithen disconnected the coax from the antenna and checked it once again (just to verify the coax was good) and it came up with an open circuit. it was suggested I pull the coax off the antenna once again today and read the resistance in the antenna. I'lldo that when I become more conscious this morning. Would a powdercoating on the mast cause lack of grounding for the mount? I wouldn't think so since it's electrically applied, but who knows.

Sounds like your mount is shorted. Make sure the plastic insulating washer is installed correctly.

[Aviator]

I believe it's installed correctly...I have had issues with these plastic washers in the past though too. Just check the resistance at the antenna between the hot side and ground side for the SO connector and got .3 right there.........between the SS spring and the mount on the mast I got a high of 177.2 and between the hotside of the SO259 and the mast Igot an opencircuit there....My back's killin me so I don't have the ability to think straight...can someone elaborate (IE dumb down) my findings for me? Thanks....

['Doc]

Center pin of the SO-239 to the whip or spring should show a short, or VERY low resistance. Center pin to the mast should be infinite resistance, an open circuit (same for the whip to the mast, open circuit).

Stick a 102" whip on top of a typical ball mount. The antenna starts where the coax stops, at the bottom of that ball-mount, so add the ball-mount's length to that 102" to get total length of the antenna. Typically, that's about 106". Add a 6" spring to that and you got 112" of antenna. (Do the math with that '234' figure, it really does work, believe it or not.)
- 'Doc

[Aviator]

My antenna was shorted out on the mount....Tryin to drop my swr some more but right now it's about 2.2....

[Aviator]

Got it down to about 1.2-1.3......now the powerlines are killin me.....anyone know a way to get the S3 noise killed or is it a just deal with it kinda thing?