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Sirio Preformer 5000 Magnet Mount Antenna

Can't see photos man. It wants me to log into Gmail. Any other way you can post them??
 
rabbiporkchop said:
Like I predicted, it went from resonant @ 27.185 without the cap hat to 19.205 mhz with the cap hat. Removing 3 feet of copper from the coil brought it back to resonance @ 27.185 mhz.
Click to expand...

Very Nice!

You just increased the radiation efficiency of this antenna by significantly reducing the losses induced by the inductance in the loading coil by adding top loading capacitance. How much can truly be determined if you did an A/B test beforehand. You should also notice a significant increase in bandwidth.

Glad to see you took a hands on approach to improve on this antenna's original design.
 
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I have cut (nibbled) 1 1/16in. off so far...kind of scared to cut more.
At time I now am at:
26.965: R=41, X=11. SWR=1.3 (this is the brake point FROM 1.2 to 1.3)
27.555: R=64, X=7. SWR=1.3 ( this is the brake point From 1.2 to 1.3)
BEST "X"=0 : 26.834 with R=70
BEST: "R"=50: 27.272 with X=11
SET UP IS:
16in. rg8x (jumper) to mfj 915 (1:1)
to mfj 259c via 18ft.rg8x
I just got a now FT 450D (yaesu) with "auto tuner" and dont want to wreck it first time tx.
Got to have antenna right.
so cutting more will help you think?
 
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X is far more important than R when it comes to tuning, and if it were me I would trim it until X = 0, irregardless what R ended up being, as long as it was within a reasonable range. That being said, your antenna will work just fine as it is. No one will notice the difference between what you have and a so called perfect setup.


The DB
 
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Yep. Get the X down to 0. You might also try removing the 1:1 balun and try it that way. Just some food for thought. Also you can try tuning antenna with the 18ft coax jumper as well. Just to see what happens. Just some food for thought. And also is the box you have the ground strap going to bonded to the frame and is it made of steel or aluminum. Might also try removing it and see what happens. You should have a good connection on the underside of the mount. Bare metal to bare metal with some NO-OX added to all connection points as well. Doing some experimenting won't hurt anything and may help your actual match or may not. Won't know unless you try. But as said. I would get the X value to 0 then focus on the rest. JMHO's.
 
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The DB said:
X is far more important than R when it comes to tuning, and if it were me I would trim it until X = 0, irregardless what R ended up being, as long as it was within a reasonable range. That being said, your antenna will work just fine as it is. No one will notice the difference between what you have and a so called perfect setup.


The DB
Click to expand...
Going to work on it tomorrow. MY Best "X" right now is X=0 w/R=70 on 26.834 at swr of 1.3
 
222DBFL said:
Yep. Get the X down to 0. You might also try removing the 1:1 balun and try it that way. Just some food for thought. Also you can try tuning antenna with the 18ft coax jumper as well. Just to see what happens. Just some food for thought. And also is the box you have the ground strap going to bonded to the frame and is it made of steel or aluminum. Might also try removing it and see what happens. You should have a good connection on the underside of the mount. Bare metal to bare metal with some NO-OX added to all connection points as well. Doing some experimenting won't hurt anything and may help your actual match or may not. Won't know unless you try. But as said. I would get the X value to 0 then focus on the rest. JMHO's.
Click to expand...
Will work on it tomorrow. I will remove the mfj 915 ( 1:1), and test, then I will remove bonding straps from mount to tool box, and test. Tool box is aluminum, bonding straps copper, and the tool box lid is bonded to the side od the tool box, and then to the top rail of the pick up bed which is bonded to the cab of the truck, and frame and hood as well....all is bonded but the tial gate, and the side doors.
I did make a contact with a friend on 27.358 lsb after using the Ft450d built in auto tuner at 70w. He is 30miles away, and down in a canyon about 45ft., and I am sitting with a 2 story bulding 45ft. away from me. I had s3 noise, and was rx him at 4-5 X 9.
He is stock C.B. and no power base.
 
222DBFL said:
Yep. Get the X down to 0. You might also try removing the 1:1 balun and try it that way. Just some food for thought. Also you can try tuning antenna with the 18ft coax jumper as well. Just to see what happens. Just some food for thought. And also is the box you have the ground strap going to bonded to the frame and is it made of steel or aluminum. Might also try removing it and see what happens. You should have a good connection on the underside of the mount. Bare metal to bare metal with some NO-OX added to all connection points as well. Doing some experimenting won't hurt anything and may help your actual match or may not. Won't know unless you try. But as said. I would get the X value to 0 then focus on the rest. JMHO's.
Click to expand...
If I change my feed line lenght (coax) arnt I just moving the SWR NODE to another point?
 
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There is no such thing as an "SWR NODE", if the SWR on the feed line changes when changing length, then you have other problems that you need to deal with such as common mode currents or a ground loop. If your antenna system is working correctly, SWR should not change with feed line length, unless it is a long run of feed line, at which point SWR will get slightly better with length, but it generally takes a lot of length unless you are using a chinese brand RG-58 or something like that...


The DB
 
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The DB said:
There is no such thing as an "SWR NODE", if the SWR on the feed line changes when changing length, then you have other problems that you need to deal with such as common mode currents or a ground loop. If your antenna system is working correctly, SWR should not change with feed line length, unless it is a long run of feed line, at which point SWR will get slightly better with length, but it generally takes a lot of length unless you are using a chinese brand RG-58 or something like that...


The DB
Click to expand...
The "node" I got from reading K0BG.com
MY coax is good, I hope I got it from DX engineering (rg8X).
 

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