Sirio Preformer 5000 Magnet Mount Antenna

[Mudduckmobile]

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?

I have so much bonding...motor to frame, frame to cab, bed, and bed to tool box, to box to cab, and bed to cab, under the head liner the 4in breadlove mount has a bonding strap going to a cab crash bar, and the hood is bonded to thr fender, and to the frame. The exhaust pipes are bonded every 2ft. to the frame too The only thing not bonded is the tail gate to bed. I bond.

 

[Mudduckmobile]

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.

I bond.

 

[Mudduckmobile]

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?

Lots of bonding. I will put in new, once more coax, and see how that goes, and mybe try a coil in the coax too.

 

[Mudduckmobile]

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.

Just moved my X=0 to anew point.....

 

[222DBFL]

Where is it resonant at now? I really hope you get it all squared away man. You really have spent a lot of time on it!!

 

[Mudduckmobile]

Where is it resonant at now? I really hope you get it all squared away man. You really have spent a lot of time on it!!

27.385
X=0, R=52. swr=1.1

 

[222DBFL]

Damn good!!! That is a good reading man!! I would leave it be. JMHO. Won't get much better than that!! What all did you change? Or add? Good job man!!

 

[222DBFL]

Like my local pal says. Glue it there and leave it!!!

 

[Mudduckmobile]

Like my local pal says. Glue it there and leave it!!!

Yes, at last. 6 snap-on mix 31 beads first bead 4in. from antenna, butted to each other, and moved the stinger UP 1/32 of an inch. I all so put alittle dab of no-ox under the breadlove mount to the cab. I also put one more bonding strap on the under side of the mount (in cab) to the roll frame in the cab roof.

 

[222DBFL]

Good work man! Was worth the effort looking at the results IMO. Glad you got it right!! Hope you enjoy the heck out of it!! Nothing like doing some thing good then being able to get out like you want!!! Enjoy my friend.
73 and God Bless.
222 Daytona Bch., FL
Sean.

 

[Mudduckmobile]

Good work man! Was worth the effort looking at the results IMO. Glad you got it right!! Hope you enjoy the heck out of it!! Nothing like doing some thing good then being able to get out like you want!!! Enjoy my friend.
73 and God Bless.
222 Daytona Bch., FL
Sean.

Thank you very much. You gave me lots of help. Thank you to everyone that helped!

 

[222DBFL]

No worries man. The DB helped the most. All I did was to provide some of the experience that I've had with the Sirio performer 5000's, turbo 5000, and the hi power 4000. All did a good job for me and made me many contacts while being on the road. Helps when the conditions are good too.
Just glad you got it all resolved and right. I truly hope you enjoy it man! Have a great time.

 

[Marconi]

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

DB, attached below is an Antenna Work Sheet I use to check the bandwidth and tuning of several antennas I have. This one is the Starduster like antenna I make called the Marconi. It is made from 5 x 102" whips. I use a mobile mirror mount and the hub from an A99 for the 4 slanted down radials. The antenna has always served me well and produces a very good match at the feed point and at the end of a working feed line. Sorry the print is old and in pencil so it may be hard to read.

(edit) You may need to zoom-in lager to read better.

I did these readings with my Autek VA1 analyzer. The VA1 is not perfect with (X) impedance showing to be off by about +6 ohms when tested against the resistor test kit that comes with the meter.

I would predict that if you used your VA1 on a similar antenna you would likely see similar results. The resonance for this design, being a bit short at 102" inches...should show to be a bit higher in frequency than the center of CB...and in my view this is what is noted here.

I also note that the value of Z for this setup is very consistent near 50 ohms across a very broad bandwidth of near 4 MHz <2.00:1 SWR which I also see with the feed line attached and when real world testing.

 

[Marconi]

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?

Mudduck, all the numbers above look very impressive...being so near perfect and all. Can you explain how a mobile antenna can show an impedance range over nearly the entire CB band with a value of X = 0?

This is not what I see on the output of my old Autek VA1 I posted above. As noted...there the value of X (reactance) varied from channel to channel across the CB band and more, from 25.520 - 29.470 MHz, and this is what I would expect.

I do see the value of Z, the complex value of the match in my report being very close to 50 ohms however. Is your meter also showing us this complex match. Do you think that when adding your 18' feet of coax the antenna system indicated CMC as a result of some reactance present at the feed point, rather than the X=0 reported?

My Marconi antenna is not a mobile install however and IMO has a more traditional ground plane attached which might provide for better matching. That said however, my meter still does not show a perfect match, but it gets close at 27.605 mhz.

Just curious, do you have any pictures of your mobile antenna hooked to the 259c at the feed point and/or the transmitter end of a working feed line...showing the values above with X=0 across nearly all of the CB band?

This is a good thread, thanks.

 

[Mudduckmobile]

Mudduck, all the numbers above look very impressive...being so near perfect and all. Can you explain how a mobile antenna can show an impedance range over nearly the entire CB band with a value of X = 0?

This is not what I see on the output of my old Autek VA1 I posted above. As noted...there the value of X (reactance) varied from channel to channel across the CB band and more, from 25.520 - 29.470 MHz, and this is what I would expect.

I do see the value of Z, the complex value of the match in my report being very close to 50 ohms however. Is your meter also showing us this complex match. Do you think that when adding your 18' feet of coax the antenna system indicated CMC as a result of some reactance present at the feed point, rather than the X=0 reported?

My Marconi antenna is not a mobile install however and IMO has a more traditional ground plane attached which might provide for better matching. That said however, my meter still does not show a perfect match, but it gets close at 27.505 mhz.

Just curious, do you have any pictures of your mobile antenna hooked to the 259c at the feed point and/or the transmitter end of a working feed line...showing the values above with X=0 across nearly all of the CB band?

This is a good thread, thanks.

No prob. I'll post some pix. prob. sunday. we just got my wife out of the hospital and need to do family right now. just got home a bit ago and looking at my thinks before bed. GN