SWR problems, mobile.

[Mudduckmobile]

SWR probs.
Everything's working good...Then swr goes nuts. connector is bad, cox is over one year old so replace cox, and connector's...put antenna back in to mount 1.5swr, 34 ohms, X=8, 9 10.....27.2850, 1.5, 34 ohms. 27.750
33 ohms , X= 10.
useing 259c (that works). cox tests good. Antenna is DX-Fighting stck/ 102 whip as stinger. this has never been bad to me. spent almost 5 hours outside today replaced EVERYTHING 2, 3 times. used 108 whip still not working. used "antenna expert" as well...nothing. I'm at the point when I'm ready to drive 324 miles round trip to the other side of the mountain to the radio shop and have an antenna and new cox put on for the first time in my life.....I'm pulling my hair out, and i,m bald!!!!!!
What am I missing?

 

[midnight special]

if swr is 1.5 ,,, if i read that right what is the problem? what you have there sounds normal for most antennas i have ever done,,,, i need to look up a dx fighting stick,, dont know what one does or looks like,,,,

 

[midnight special]

ok after seeing a few what i think was a fighting stick,,, need more info where is this mounted at and on,,,, and at 12 feet long like to know more info about the aluminum extension,,,

 

[loosecannon]

is it a 50 ohm antenna?

a properly working 102" whip will show an SWR of 1.5 and has an impedance of about 36 ohms.

not sure the specifics of a "fighting stick", but if you can post them, we might be able to help.
LC

 

[midnight special]

from what i googled and dont really understand how it works ,,never seen one before,,,,looks like a 36 inch extension with a 102 inch whip on top,,,,,youtube had a vid of one mounted on a truck bed and at 12 foot plus tall it was way up in the air,,,,

 

[222DBFL]

Might want to stick a dummy load at the end of your coax, like where the antenna mounts at. Check for any issues starting from there back.
Or vise versa. Stick the dummy load at the back of the radio ad well to make sure all is good out of the radio. You will need to have an swr meter obviously when doing this, so connect dummy load directly to ant port of swr meter. And make sure to use same jumpers as if you had a meter in line and using. Hope this makes sense. But starting at the end of the coax, using a radio and swr meter, and a cheap radio, just check VSWR first. Then go from there, replacing radio and such with your mfj meter from radio to where antenna mounts at. If possible, place dummy load onto the mount itself. That is the end point and if possible should be the start point for s dummy load.
At any rate, hope you get it resolved. Good day.

 

[fourstringburn]

You just learned that the 102 whip is not the perfect antenna (SWR wise) as many people claim.

Yes the impedance should measure around 37 ohms since it is 1/2 of 1/4 wave dipole antenna. While this isn't too critical, it does represent a feed point current loss but that's the trade off as opposed to using a mobile antenna with a loading coil.

You probably are aware shortened mobile antennas have loading coils. This coil is needed to match the antenna feed-point if properly designed to 50 ohms or close to it since the antenna is shorter than a 1/4 wave length and the impedance is increased.

However, even though loaded antennas may have a 50 ohm feed-point, the trade off here is losses within the coil itself so the effective radiated power (efficiency) is decreased by as much as 20% or more on 11 meters and reduce even at higher percentage losses at lower frequency amateur bands. This is the price you pay for running mobile antennas especially at lower frequencies, but it does let you work the bands at least. With the 102 whip, you don't have any coil losses so the efficiency is much improved over loaded coil antennas.

If you insists on perfection for your 102 whip, get some 12 gauge enameled wire like the type used for electrical motor winding's and wind 7 turns around a spark-plug's thread with an inch or so left over on each end and scrape the enamel off both ends to solder on 2 terminal rings, then attach 1 ring to your antenna feed point on the "Hot" side and the other to the ground side of the antenna, usually the mounting bracket bolt. This creates a shunt matching coil.

Now use your analyzer and check impedance. You probably will have to gently stretch the coil some or compress it until you get a 50 ohm reading. Take note on the impedance change with every adjustment so you know which way to go. You may have to add or subtract a coil turn to get that elusive 50 ohm match. Most likely you will get a near perfect match on a 102 whip around 27.700 MHz. Add a spring if you want it closer to the CB bands but the bandwidth is very wide on 102 whips so that it isn't really necessary unless you are hung up on SWR.

Below is a pic of an HF mobile antenna from underneath the trunk with a loading coil. Note this one appears to have a coil tap to use for different bands since impedance vary especially on lower bands. Notice one coil leg on the hot side coax and the other is grounded.

 

[Mudduckmobile]

This is the DX-Fighting Stick / with a 102in whip as the stinger.
The bottom of the whip is cut off, and then incerted ion to the DX-stick, this gives 30in of tunning.
before my problems I had: 44 ohms X= 3,4,5. and an SWR of 1.1- 1.2 from 27.2800-27.7025.
I am going to try the coil today as you have shown me Fourstringburn. I will also be doing the full retesting with dummy load at all points.
Thank you for input back to you soon with.........

 

[w9cll]

Also look at this site - http://www.k0bg.com/

 

[Mudduckmobile]

Also look at this site - http://www.k0bg.com/

Been there today, more reading to do

is it a 50 ohm antenna?

a properly working 102" whip will show an SWR of 1.5 and has an impedance of about 36 ohms.

not sure the specifics of a "fighting stick", but if you can post them, we might be able to help.
LC

yes

 

[Mudduckmobile]

if swr is 1.5 ,,, if i read that right what is the problem? what you have there sounds normal for most antennas i have ever done,,,, i need to look up a dx fighting stick,, dont know what one does or looks like,,,,

http://www.ebay.com/sch/i.html?_fro...ng+stick.TRS0&_nkw=DX+fighting+stick&_sacat=0
Info. on the fighting stick.

 

[Mudduckmobile]

if swr is 1.5 ,,, if i read that right what is the problem? what you have there sounds normal for most antennas i have ever done,,,, i need to look up a dx fighting stick,, dont know what one does or looks like,,,,

R, and X factors are not close to past readings, and swr is way out too...I would think things would be same or better when replacing bad connector....and new cox.

 

[222DBFL]

Is the coax that you replaced of the same type and length? This may be why you are showing different readings as well. You might try adding a barrel connector and extending the current coax by different lengths if you can, just to see if it makes any difference. Just some food for thought. Also just to make sure, re check the new connector you put on as well as the new coax. Look for any pinching or flat spots in the coax as well as checking the connector. If you can, take it back apart and redo it. Never hurts. Hope you get it resolved.

 

[midnight special]

hmmm a lot of money just for a adjustable whip antenna,,,, i think i will stay with my 102 inch whip i have had for 30 plus years,,,,,,

 

[loosecannon]

i don't see any sort of tuning going on with that antenna.

it seems like the base is just a way to mitigate the sway of the antenna when driving at highway speeds, while providing a way to adjust the length of the antenna.

this could be useful if you choose to run without a spring or something like that, but you should never need more than about 8" of adjustment.

at the end of the day this is a quarter wave antenna, and should be adjusted as such.

if you are running it without a spring, adjust the total height of the antenna to 108".
if you are using a spring (i think i see one in your picture) then subtract the length of the spring from the 108" length.

then, adjust the length of the antenna in 1 inch increments so that the dip is where you want it with regards to your frequency range. most do it for channel 20, but you may operate in a different portion of the band predominantly.

the SWR should dip down to about 1.5 in the center of the range, and your 2.0 SWR points should be at least 500khz in either direction if not more.

i do not own one of those antenna analyzers, but my guess is that you have an antenna that should have an R of 36, and are trying to tune it for an R of 50.

my educated guess is that your old reading of 44 was only possible because of the losses in your system, and were actually indicating that you had an antenna problem.

now your system is working properly and won't allow you to achieve that false 1.2 SWR reading.

a quarter wave antenna is NOT a 50 ohm antenna, and should not be treated like one.
LC