SWR problems, mobile.

[Mudduckmobile]

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

LC:
I have been a dimwit... for some reason I forgot everything I have been schooled in Whip antenna(s).
I spaced on the whip NOT being 50 ohms...It's more 36-37 ish, and I have always tried to make it as close to 50 ohms as I could, with the lowest swr...I don't know why I have not fried something.
I also think I may have found the problem, it looks as I may have pinched the coax in the hood. I am thinking about removing the base I'm using now and putting on a base that will let me use eyelets on the end of the coax. to solve my "hood pinching" problem, I am thinking about soldering a 4in. hank of 12g stranded to the sheild, and also a hank to the center of my coax, dress the coax end with Liquid tape to close, and crimp/sloder my eyelets to the 12a and then tighten to the antenna as norm. I have made a coil as well to try out After I can get thins ironed out.
And yes I know the DX-stick is a bit long. I'm going to cut it to 12in. and make two out of the one, and have some scrap for other projects.
I always try to keep the swr down to protect my amp.

 

[Mudduckmobile]

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.

Done for the day...wife is ready to kill me...I have 75ft. of coax (new) and 6 new ends. I will get back on it in the AM.
I was hear'en good DX today here in the N.W.C. just could not make it out today. My mind when blank, I started to get frustrated, and all went to hell....You all have got my mind right, and going over K0bg site has helped too, to wake up my brain.

 

[fourstringburn]

View attachment 18060 View attachment 18061
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.........

Never seen a setup like that. I would say that is ideal in the fact you can lengthen the whip for the CB band since a 102 whip is a little short. You could also mark the whip with a sharpie for 10 meters so you can easily tune it there if needed. You should be able to cover 12 meters and possibly 15 meters since a 1/4 wave would be just over 10 1/2 ft. To do this you would definitely need some inductance matching.

Interesting why your analyzer originally gave pretty good readings before but your newer readings are what you should expect to see now. I checked 102 whips before and the impedance usually shown a value between 34 to 37 ohms.

Be sure if you try the shunt coil that you install at the antenna feed point to be most effective. The purpose of this coil is to add some feed point inductance rather than using a lossy coil in the antenna itself to match the feed point impedance to 50 ohms.

 

[loosecannon]

MDM, as long as you keep those "hanks" under about 3" or so, i think you will be fine with that.

i do think that is a very strange place to mount an antenna that large .
the looks you must get going down the road!

FSB- my guess is that it was one of those "the closer you get to a dummy load, the more broadbanded and less reactive antenna you have" type of situations where the losses in the system compounded to produce a lowered radiation resistance which led to him being able to futz together a ~50 ohm "load".

now he has raised his radiation resistance to the point where the peaks get sharper and the dips get lower, and he can't attain the same readings.

This is a good thing MDM!!!
i bet you will notice an improvement in your RX and TX.

also, i understand about keeping the reflect low if you are running big power. (most people who use a fighting stick or similar antenna probably are)

use the shunt coil trick FSB showed you, and you should be all good.

if it were me, i would make up a 6 turn, a 7 turn, and an 8 turn coil each with a 1:1 ratio of length to diameter. (this means that each coil should be about .5" in diameter, and about .5" long)
put lugs on each of your coils (soldered AND crimped), then try them each out before you start spreading or compressing the turns for fine tuning.

find the one that gets you as close to 50 ohms as possible, and then tweak it a bit to get things where you like them.

i think it's important to get your antenna tuned to the "1.5:1 SWR dip" i described earlier before you start messing with the shunt coil, but really that's just my opinion.


personally, i LOVE! using shunt coils in mobile installs (almost as much as i love using CM chokes at the feedpoint in mobile installs) because of the DC grounding.

this is a HUGE deal IMO, and can really make a difference in the static you hear in your receive.

best of luck, and please post your results.
LC

 

[Mudduckmobile]

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

LC: There is an old school s.s.spring on the mount I had from around 1975 when I was a youngster, next is the DX-fighting stick, into that is a 102 s.s.whip with the bottom end cut off. From the bottom of the spring to the top of the whip, with the whip all the way down is 105in., With the whip all the way up it is 135in.
I have to have the spring as at hwy speeds it was torquing the mount to much, now with the spring at 50mhp it starts to flex, and at 65mph lays back about 5*- 8* .
We live up in the "high desert" of Cent. Or. and there's nothing to bang into...for the most part. When we go the" big city" over the hill, Portland, I put on my Monkey made mm-9 long /w s.s.spring. Oh, the Fighting stick is 7/8in.dia. I use to run a spring,102 whip and it all worked good, but.....always looking for better, most of the time I have it and just don't "see it". It's like when I can talk to Sao Paulo, and can hear someone from Santos a few miles away and can't work them....I know it's "conditions" but I still want it, I want my moblie to work like a base....it's not to be but I try. It's fun.

 

[loosecannon]

i hear ya MDM. i too have spent many hours in my truck DXing.

I made an adjustable 1/4 wave antenna out of two pieces of thin walled aluminum, and brazed on a 3/8X24 stud.

it was only for sitting still but worked great.

if it were me, i would get rid of that old spring and replace it with a new one from Hustler.
if there is one weak point in your system that you have not addressed, it is that spring.

remember that inside that spring is a copper braid which has been exposed to the elements for more than 30 years.
it may be fine, but i would not trust any copper that had been outside for that long.
just my opinion here.
LC

 

[Mudduckmobile]

i hear ya MDM. i too have spent many hours in my truck DXing.

I made an adjustable 1/4 wave antenna out of two pieces of thin walled aluminum, and brazed on a 3/8X24 stud.

it was only for sitting still but worked great.

if it were me, i would get rid of that old spring and replace it with a new one from Hustler.
if there is one weak point in your system that you have not addressed, it is that spring.

remember that inside that spring is a copper braid which has been exposed to the elements for more than 30 years.
it may be fine, but i would not trust any copper that had been outside for that long.
just my opinion here.
LC

Very good point, I'll order one up.
For Dx in the field, and after just using a wire dipole that I put up with a 25ft.painters pole, and 8ft. pvc pipe, giving me, as a rule 30ft off the ground. The boss (wife) gave me a moxon wire antenna that I put up on the pole, and rig down. It is quite a mess to put up, and we will do so some time this summer when Dx gets better....I hope. we have a camp spot at about 8000ft we go to, and I do my best Dx from there

 

[M0GVZ]

Is the mount a lip mount on the hood or fender? I'm sensing a grounding issue going on.

 

[Mudduckmobile]

I have been in and out just looking at the site.....Had some things to do and radio got put on the back of the shelf...
I am still up in the air on this antenna thing.The truck is bonded EVERY where top to bottom, inside and out...I have tried two new mounts, in 3 locations. New coax 3 times. Used a friends mfj, used my mfj, used the antenna pro.
Back story Everything worked great. Then got odd swr readings, found out coax connector, (male) at the out bound swr/power meter was lose at the center, so I just replaced the coax too (it was one year old in the mobile).....from this point crap swr's, R= junk, and X= junk, so it's come to the point I'm going to take it in to the radio shop and have them put in a new antenna system, all coax's radio to meter, to antenna....it's the craziest thing. I was up running the 108in. whip at swr 1.3 (with power 1.5) and an R=38, X=7. got some so.cal skip on lsb38, and a little action on .555 (usb) out of n. mexico but it was Short action, maybe 4 hours here in cent. oregon. Everyone had me at "59' 59++" you know how that can be....I had them at 37, 46, ...and so on.
Any way, the wife's transplant is acting up, and we have been tied up a the doc's, so when were up at the hospital the truck will be at the radio shop. 73

 

[Mudduckmobile]

I at last got everything working.....Thank you to all who helped!!! 73

 

[Mudduckmobile]

 

[M0GVZ]

Excellent install there. The MFJ-259 in the first picture showing 26.800MHz was showing an almost perfect feedpoint impedance for a quarter wave over perfect ground of 36.9 Ohms at resonance (X=0) so you're only 1 Ohm out. Takes a lot of work to get to that point and I think we can pretty much say that the antenna install is going to be as good as it gets from a grounding point of view.

 

[Mudduckmobile]

Thank you M0GVZ.
I Just sat down and tried everything that folks suggested. I first had a coax pig tial I made 1in. long to put at the antenna and started tuning. I wrote everything down, found what was best and then moved my analyzer to the radio end of my coax, I added 9 in total mix 31 split beads on my coax and everything came back to me as it was at the antenna base.
The set up seams to be working well. One of my daily contact group members about 62 miles out from me had me 49 he told me and that was up 2-s from what I was in the past running at 25w, usb 27.405. At full power I was 59++ at 250w he is a base. I mobile.

 

[fourstringburn]

I added 9 in total mix 31 split beads on my coax

That's a lot of ferrite beads... Have you tried coiling the coax close to the feed point with 7 turns and using just one or two 3/4 in. ferrites?

This should alleviate a lot of the CMC and create some inductance as well but not as much on higher frequencies above the 30 meter band like the lower bands.

Glad to see you are getting in there and trying to see what works best since every mobile install is somewhat unique to itself.

Keep on posting your findings here for all of us to see!

.

 

[Mudduckmobile]

That's a lot of ferrite beads... Have you tried coiling the coax close to the feed point with 7 turns and using just one or two 3/4 in. ferrites?

This should alleviate a lot of the CMC and create some inductance as well but not as much on higher frequencies above the 30 meter band like the lower bands.

Glad to see you are getting in there and trying to see what works best since every mobile install is somewhat unique to itself.

Keep on posting your findings here for all of us to see!

.

I was going to but I tried the beads and they worked so I stopped at that. Monday I have some time and I am going to put in a longer coax between my amp and radio, 9ft. lone at this time it is 2 ft. long, then I will check everything....but I will remove the beads and try the coil at some point in the re workings....Right now its rocken...If I can get it better I will.