variance in swr readings

[W5LZ]

Your results are showing that the antenna is very close to 'right', or resonant at 27.555 Mhz. That's where the lowest 'X' is. It also shows that while the SWR is the same for 27.555 and 26.965 Mhz, it won't work as well at that 26.965 Mhz frequency (efficiency) because of the 'X' being twice as much. It also shows that SWR alone isn't telling you much since it says that antenna is doing well in two places that are not harmonically related (just can't happen that way).
Was there some frequency between 26.965 and 27.555 where the 'X' was lower and the 'R' was close to 50 ohms, maybe around 27.260 Mhz?
- 'Doc

 

[Whiplash-265]

Was there some frequency between 26.965 and 27.555 where the 'X' was lower and the 'R' was close to 50 ohms, maybe around 27.260 Mhz?
- 'Doc

do you mean an incoming frequency? i never thought about that, that the antenna might still be "active" on the receive during such a test thus affecting results. Will run another set asap with multiple samples (1/20/40/55/etc) as well as find where i have a r=50 and x=0.

as always, greatly appreciate the help!!

 

[Whiplash-265]

latest

26.555 r=100 x=10 swr=2.2 z=109 %=84
26.655 r=102 x=06 swr=2.0 z=103 %=87
26.755 r=95 x=0 swr=1.8 z=94 %=90
26.855 r=85 x=5 swr=1.7 z=86 %=92
26.955 r=75 x=12 swr=1.5 z=77 %=95
27.005 r=67 x=13 swr=1.4 z=68 %=96
27.155 r=59 x=13 swr=1.3 z=60 %=97
27.255 r=52 x=11 swr=1.2 z=53 %=98
27.355 r=47 x=9 swr=1.2 z=47 %=99
27.455 r=42 x=7 swr=1.2 z=43 %=98
27.555 r=38 x=6 swr=1.3 z=39 %=97
27.655 r=35 x=7 swr=1.4 z=36 %=96
27.755 r=32 x=9 swr=1.6 z=34 %=94
27.855 r=30 x=8 swr=1.7 z=32 %=92
27.955 r=28 x=8 swr=1.9 z=30 %=90
28.005 r=27 x=6 swr=2.0 z=28 %=87

so my best x is at 26.765, best r is between .255 and .355
best efficiency reading is at .355, exact 50 ohm load is at .280 (with an x=10)

so if i'm after overall efficiency i still need to shave off another 1/4" or so from the whip to pull me into the ".555 premium" target area

puzzling but even at what appears to be my "prime zone" i get return loss readings that unless i'm reading things wrong or running a test that doesn't apply to coax + antenna (which IS quite probable) seem high?
at .255 i get an rl of 19db/.1, .355 20db/.09, .455 18db/.1
at my best efficiency (99%) am i experiencing a 20db loss? i fail to see the efficiency in that LOL

again, thanks for letting me pick your brains guys...you're saving me smoking equipment through the learning process

k, it's Monday, off to ham school...cheers!!

 

[boomer111]

Not only adjusting antenna whip length but location can change the readings. I once got a R=50 X=0 but it took many hours of fooling around with the mag mount and 10K. Going to the 22 in. bottom shaft is what finally did it in my case. In the big rig I ran the 17 in. bottom with dual coil and got very closer to the same numbers. Now for some reason best I can get is a R=57 and X=0. I think the loss is like -36db. With R=50 X=0 it was -48db which is the lowest the 259B reads...nirvana...

 

[Whiplash-265]

it's a never ending adventure boomer i had to move mine 3 " so the coax would stop rubbing on my roof but have yet to re-check it as yet. and with winter coming i don't see that happening for a few months

concentrating on trying to get a base set up as i don't see too much time spent in the mobile with all this cold weather coming....ah yes, more fun and excitement awaits lol

thanks for sharing your experiences!!

 

[boomer111]

Well that move changed things so you will have to re check it. I was dealing with 1/16 of an in. to get the R50 X0 numbers with both location and stinger length.

Another interesting thing is that it would change with regards to the Suns elevation and even direction of the car regarding the Suns position. I would always try and find a big open field to test in. No parking lots with light poles etc. This can be a difficult endeavor in a big city or even suburban environment. RF can be a finicky thing.

 

[W5LZ]

"27.255 r=52 x=11 swr=1.2 z=53 %=98"
"27.355 r=47 x=9 swr=1.2 z=47 %=99"
"27.455 r=42 x=7 swr=1.2 z=43 %=98"

Those are the three readings that are the 'best', so if you do any more adjusting, use them for reference. Personally, I don't think there would be much point to it, there won't be any perceptible or noticeable differences on your end or 'their' end.
When the 'X' get's into the single digit range, and the 'R' is 'close' to 50 ohms, it's about as good as it get's. (Nothing wrong with an SWR of 1.2:1 either.)
Expect electrical changes when there's any physical changes. Those reading are not going to stay constant especially for a mobile antenna system because it's always changing, in location if nothing else. (Sit on the side of the road somewhere and watch those meters as traffic goes past...)
- 'Doc

 

[Whiplash-265]

comments appreciated as always Gents

i think it's about the best i'll get on a single stinger..
i might chop another little bit off to pull my "gooder" readings into my more used freq. range (very rarely use the 1-40 zone and no 28k in my near future) and grab the 66" whip for the bottom end if i ever start venturing in the direction

cheers 'n beers