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Sirio Preformer 5000 Magnet Mount Antenna
- Thread starter NewYork714
- Start date
I hope I did not go to far...
In three cuttings, and testing I thought I would stop and ask question(s).
Testing with mfj 259c, and 16in. rg8x jumper(sitting in truck testing).
Range for "X"=0 is:27.335 - 27.785.
27.335
X=0, R=64. swr=1.1
27.385
X=0, R=65. swr=1.2
27.785
X=0, R=78. swr=1.5
Then the fun starts.
I removed the mfj259c, and installed my 18ft. rg8x coax.
I reattached the mfj 259c at what will my rigs attachment point, I retested.
Range for "X"=0 is:26.904 - 27.319.
26.904
X=0, R=60. swr=1.2
27.319
X=0, R=56. swr=1.0
27.385
X=2, R=54. swr=1.1
27.555
X=9, R=49. swr=1.2
what do you think?
Tomorrow I'll play with the stinger,I can move it up,it's all the way in now.
GN
Yep, not much. But remember that antenna does have a matching coil, so it might be just fine where it is. Remeber the radio wants to see a good match at this point and it appears that is the case with your actual 18ft of coax. Not saying this is correct. But it is what is being shown. I think if you raise the antenna a bit it will be good to go, but I could be incorrect. Let's see what The DB says about it if he posts again.
Also I don't see you doing much talking on 27.785, and your readings are actually not bad at all at 27.385-27.555. Not sure where you talk at mostly, but for SSB, you are very close to being about perfect, but like I said, I could be wrong. That is why I say I wouldn't mind seeing The DB post his thoughts again. Don't worry, I truly don't think you are far off at all if any depending on where you talk at mostly. But I would like to see some more posts by guys more experienced than I about it. I never had issues when tuning any of my Sirio antennas. But every install is different. Don't give up, as IMO, you are really close to being about as good as you can get. But like I said, I may be incorrect. GN, and talk tomorrow!! Be safe and hope it all works out.
Sean.
Also I don't see you doing much talking on 27.785, and your readings are actually not bad at all at 27.385-27.555. Not sure where you talk at mostly, but for SSB, you are very close to being about perfect, but like I said, I could be wrong. That is why I say I wouldn't mind seeing The DB post his thoughts again. Don't worry, I truly don't think you are far off at all if any depending on where you talk at mostly. But I would like to see some more posts by guys more experienced than I about it. I never had issues when tuning any of my Sirio antennas. But every install is different. Don't give up, as IMO, you are really close to being about as good as you can get. But like I said, I may be incorrect. GN, and talk tomorrow!! Be safe and hope it all works out.
Sean.
You should trust the numbers taken from closer to the antenna more as that is closer to the numbers of the actual antenna, and better represent what your antenna is actually doing. That being said, you need to make sure the other side of the coax has a low enough SWR to be safe to plug into your radio.
I am curious, was 18 foot coax length used because of the 18 foot rule myth, or simply what you had available? It is actually closer to 22 feet long electrically, and a bit off from half a wavelength.
Looks like you have some common mode currents on your feeline, which is more common in mobile installations than many people realize. K0BG talks about them on his Antenna Myth's page under the Coaxial Myths section, coaxial myth 2, its second aspect to be specific.
He then talked about using a coil based choke, however I would use a ferrite choke system if possible over a coil based choke if you choose to go that route as they have many advantages, including but not limited to not being affected as much (actually at all) by nearby metal should you decide to try and eliminate said common mode currents. You might try putting the balun back on for testing purposes, and see if SWR changes less between both coax that you are testing through with it on. Some baluns (but definitely not all) have the side effect of blocking common mode currents.
The DB
I am curious, was 18 foot coax length used because of the 18 foot rule myth, or simply what you had available? It is actually closer to 22 feet long electrically, and a bit off from half a wavelength.
Looks like you have some common mode currents on your feeline, which is more common in mobile installations than many people realize. K0BG talks about them on his Antenna Myth's page under the Coaxial Myths section, coaxial myth 2, its second aspect to be specific.
K0BG said:
He then talked about using a coil based choke, however I would use a ferrite choke system if possible over a coil based choke if you choose to go that route as they have many advantages, including but not limited to not being affected as much (actually at all) by nearby metal should you decide to try and eliminate said common mode currents. You might try putting the balun back on for testing purposes, and see if SWR changes less between both coax that you are testing through with it on. Some baluns (but definitely not all) have the side effect of blocking common mode currents.
The DB
Just stoped by for a mint. Raining here today so no antenna work today.
You know I dont do much lower then 27.385, and .555 is/was a good spot too, some times might come across an old friend on .775....
We got rain today, no antenna work.
The first thing I will do is put my mfj 915 back on at 16in. from the antenna, and retest. I my also try some of my snap on mix 31 beads, there the size for rg8x as I run.
I reason the coax is 18ft. is the first install thought was a longer run to mount..."It was in the mail".
So the plain is to retest with / out the mfj 915/ beads. then do it all over, after i move up the stinger 1/16in., and retest.
trying mfj 915/ beads next before I move up the stinger 1/16in. retest.
If i have to, I have one more new, unused DX Eng. jumper, and 18 ft. coax.
If the overall SWR alters by adding coax its usually a suggestion of an inadequate RF ground and the coax being part of the antenna.
A quarter wave vertical over a perfect ground plane has a feedpoint impedance of 36.8 Ohms. The further away from that you are when X=0 the more losses you have and again, for a mobile install its usually because of an inadequate RF ground. Closest I've got is 38 Ohms. Installing the whole antenna system took me over a day, most of that time spent doing bonding.
When I put a Sirio 4000 on the car recently I had to cut 3 inches off it due to the efficiency of the RF grounding on my vehicle. Prior to cutting and with the whip down as much as it would go it was resonant at 25.something MHz.
Have you done any bonding?
A quarter wave vertical over a perfect ground plane has a feedpoint impedance of 36.8 Ohms. The further away from that you are when X=0 the more losses you have and again, for a mobile install its usually because of an inadequate RF ground. Closest I've got is 38 Ohms. Installing the whole antenna system took me over a day, most of that time spent doing bonding.
When I put a Sirio 4000 on the car recently I had to cut 3 inches off it due to the efficiency of the RF grounding on my vehicle. Prior to cutting and with the whip down as much as it would go it was resonant at 25.something MHz.
Have you done any bonding?
Pretty much "SPOT ON"
I have seen so many installations where most of the emphasis was placed on adjusting the stinger length and very little on bonding, shielding, and/or uncoupling the feedline.
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