102" install

[KI4MSJ]

OK, Here's the situation. I have a ball hitch that I took the ball off of and wanted to mount a 102" whip on. I went to RatShack and bought a spring and Ball mount and put it on the hitch. Starting from the whip....

1. whip
2. spring
3. ball mount
4. rubber gasket
5. hitch
6. gasket
7. washer
8. nut
9. center connector is connected to the center stud via ring connector.
About 2" from Ball mount, I drilled a hole through the hitch for a screw which I connected the ground side of the coax. From there I connected another ground to the body but, my SWR is way out of whack. Here are my readings with a MFJ Analyzer....

144.50 Mhz-5.5@50Ohms
27.250 Mhz- 12.0@50Ohms
28.400 Mhz-14.0@100Ohms

I am trying to install this for my road trip this weekend. Any suggestions or observations would be appreciated. I do have a couple pics that I can send to your e-mail if needed.

 

[skipper1]

In my 48+ years experience with antennas I have found that when a 102" whip has a high swr 1.6.1 or higher it is usually due to the radiator being grounded or to much of the antenna below a metal object such as a tailgate or mounted to low on the fender. Most likely the whip is grounded through the the mount to ground. good luck on the install.

skipper1

 

[Marconi]

Well, just do an OHM's check on the radiator and that should tell you if the ground is a problem. What is the gasket after the hitch. If the gasket insulates the hitch from the bumper or frame and the ground connection to the antenna is connected to the hitch as noted then how does that establish a connection to ground?

I have never seen a bad SWR with a well installed 1/4 wave whip attached to a well grounded rear bumper even with the tailgate only inches away from the radiator. Now antennas with coils or that were short did react in such installs.

I do not like ball mounts. They are typically designed to change directions and they don't do that too well.

 

[SR385]

Most likely the whip is grounded through the the mount to ground. good luck on the install.
skipper1

Yup, me too me too.

 

[mackmobile43]

disconnect your coax and ground lead to the ball mount and run a continuity test from the mounting bolts to the spring to see if your mount is shorted to ground and if not check for continuity through the spring.

 

[KI4MSJ]

The gasket is between the nut on the stud from the base of the ball mount and the underneath of the hitch. Also, thanks for the suggestions. I will check the continuity

 

[Captain Kilowatt]

First off if the antenna/mount was shorted the SWR should be sky high and reading a LOT less than what you are seeing. Speaking of your readings, what is the first number after the frequency supposed to represent? Is it the SWR value that your analyzer shows or is it the reactance values? I have an MFJ-269 but the way you have written it confuses me. On 27.250 if that is R=50 ohms and X=12.0 ohms then the SWR should be quite good.You do not show anything in the CB band. I suggest removing the spring and taking another reading. I suspect the antenna is too long. I never ran a spring on my 102 whips when running above ch40 and up into 10m. SWR was always great without it.

Here are my readings with a MFJ Analyzer....

144.50 Mhz-5.5@50Ohms
27.250 Mhz- 12.0@50Ohms
28.400 Mhz-14.0@100Ohms

quote]

 

[Marconi]

I was thinking maybe there is no connection to ground in the setup due to the gasket under the hitch, rather than the radiator being shorted to ground which would likely make the SWR show infinety.

 

[freecell]

"what is the first number after the frequency supposed to represent? Is it the SWR value that your analyzer shows or is it the reactance values? I have an MFJ-269 but the way you have written it confuses me. On 27.250 if that is R=50 ohms and X=12.0 ohms then the SWR should be quite good."

this question needs to be answered first.

 

[mackmobile43]

this thread needs pictures

 

[freecell]

not really, just an answer to QRN's question.

 

[W5LZ]

I'm confused. Considering the frequencies the antenna was checked at, what band(s) were/are you planning to use this antenna on?
- 'Doc

 

[mackmobile43]

not really, just an answer to QRN's question.

humor me

 

[freecell]

looks like you'll have to wait until he returns from that weekend trip.

using the trailer receiver hitch for an antenna mounting location always guarantees increased power losses resulting from stray capacitance between the antenna and the back side of the vehicle in parallel and increased coupling to earth ground bypassing the required coupling to the vehicle body mass, one of the many reasons why the antenna is more efficient when the vehicle body is directly underneath it instead of next to it. the mounting location in this instance actually adds more signal loss.

 

[mackmobile43]

looks like you'll have to wait until he returns from that weekend trip.

using the trailer receiver hitch for an antenna mounting location always guarantees increased power losses resulting from stray capacitance between the antenna and the back side of the vehicle in parallel and increased coupling to earth ground bypassing the required coupling to the vehicle body mass, one of the many reasons why the antenna is more efficient when the vehicle body is directly underneath it instead of next to it. the mounting location in this instance actually adds more signal loss.

so true