Tuning the MFJ SPT500 Super Penetrator

[Needle Bender]

That's odd, unless they've recently changed the design because the one I helped assemble was 22' 6.5" tip to tip plus the 9.5" top hat radials and it dialed in nicely at 27.295.

But I believe I understand now that you were referring to the bottom tube of the radiator which is 72" long.

 

[Ferrarimx5]

My P500 came with pre-bent 45° downward top hat rods.

.

Interesting.. I will have to try bending mine down.
When mine sit straight out we have an OWL that loves to perch on top. He broke the top section which I had to replace.

If I bend the top hat rods, the Owl will not have a place to perch.
All will be well with the world.

 

[Ranch55]

Don't you mean 23' 3" TOTAL radiator length? Are you still using the top hat radial rods?
My old school P500 required a 23' 3" tall radiator w/o top hat rods. That's right at .625 for 27.275MHz above the radial plate.

No, 23' 3"~4" will be the correct finishing spot .......
My dialed in at 268" .......

 

[M0GVZ]

Kinda getting off the topic. First S-meter readings are relative and not absolute. Maybe a little subjective depending on who's looking. A true 5/8 GP tuned properly should present about 3Dbd of gain.

Might do if you're in the marketing team of an antenna manufacturer but more importantly, at what angle? Modelling pretty much everything end fed from a quarter wave to a 3/4 wave shows very little difference in gain at low angles. At higher angles that are of little use though it gets more interesting as you get lobes appearing in the longer antennas.

 

[Ranch55]

NB, as reported to me by a couple of other NSP500 operators...my dimensions show overall length of 264" inches, 22' feet from the feed point base to the top hat that has 4 x 10" inch wires. The tip tunable wire #1 = 40.5" inches was reported for the CB band.

The radials are 105" inches, and base assembly wire #5 is 72" inches.

My experience with Internet reports trying to secure accurate antenna dimensions are sketchy at best and I'm not even sure about these dimensions, so these measurements may vary from your results.

My previous post above was incorrect.

My old school Penetrator 500 (late 1970's model, new out of the box in May 2016) ended up at 263 3/4" (21' 11 3/4") centered on 27.350 mhz with 1.01 SWR, R=51.6 ohms, X=.46 ohms.
This was measured with a MFJ 259C analyzer, and a Rig Expert 54 Zoom analyzer. Both instruments matched readings.
268" (22' 4") centered the antenna at 27.080 mhz.
265" (22' 1") centered the antenna at 27.205 mhz.
All measurements from bottom of bracket where connector is (excluding the connector), to the top of the screw that attaches the 4 top hat radials.
And the Top Hat radials are bent down at a 40 degree angle from horizontal.

I also did some upgrade modifications to the antenna.
I removed the very bottom insulator and replaced the small 20ga wire with a 12ga teflon coated silver plated wire. I replaced all the threaded hardware with stainless steel screws, nuts, washers.
I sealed the bottom insulator when I reinstalled it.
I upgraded the coax connector with Amphenol silver plated, teflon insulated connector and sealed the flange to the bracket with Jet Lube Pure Copper connector and joint sealant.
I wrapped the bottom vertical radial from the bottom of the upper insulator down 4 " using self sealing silicone coax wrap and wrapping that with Scotch Super 88 tape.
I did the same on the top of the insulator.
All vertical radial joints, and horizontal element joints are coated with the Jet Lube Pure Copper before assembly. Then they are clamped. At each overlap joint just below the clamp, I drilled a 1/8" hole and installed a #6 stainless steel metal hex head screw.
I then wrapped ALL overlap joints with silicone coax wrap to seal out the weather. then wrapped all the coax wrap with Super 88 tape.

 

[old goat 321]

All good info Ranch. I just picked up a used Penetrator. The operator said it was erected in 2012. Im in the process of cleaning the slip joints and checking for cracks and such. I read your post on making a new top insulator with ptfe pipe. Im kicking around the idea of using double walled sealing shrink tube rated to 600 volts instead. I would like to rid the antenna of the hose clamps and use screws instead. Then use a high quality adhesive shrink tube to weather proof the joints and possibly add some stability . Im a novice in these matters and defer to the more experienced. Are there any flaws in my approach ?

 

[Shadetree Mechanic]

Stainless hose clamps are better than screws. Use an antiseize compound with copper in it to help conductivity.

 

[Ranch55]

After I have the antenna tuned, using an antenna analyzer, I do secure each joint with a small stainless steel metal screw. And I do also use the stainless steel hose clamps.
I then wrap each joint, including the hose clamp, with self-bonding silicone coax wrap. I then wrap it with 3M Super88 tape.And yes, I also use copper lubricant made for antennas and electrical connections, on each joint.

 

[W4KVW]

MFJ can screw up a water sandwich.They use cheap labor & cheaper materials.They made Cushcraft far worse than even when Cushcraft built them.

SIX-SHOOTER

 

[JAF0]

Lose the top hat.

Place a tight fitting rubber cap over the top.

Make it 268" from the ground radial bracket to the tip.

Install.

Enjoy.

 

[old goat 321]

Thats just the kind of info im looking for. I have a used Galaxy 2547 thats .0005 off freq. A used A99 thats splintered, a used good looking Penetrator, thats going on top of my used 34' tv tower. The only new stuff will be 100' of TM LMR 400 and a MFJ-872 swr meter that i bought a while back. I just want to set it, erect it, and use it. Mostly base to mobil on ssb. Maybe send the base out for a freq alignment and clarifer mod.

 

[JAF0]

Thats just the kind of info im looking for. I have a used Galaxy 2547 thats .0005 off freq. A used A99 thats splintered, a used good looking Penetrator, thats going on top of my used 34' tv tower. The only new stuff will be 100' of TM LMR 400 and a MFJ-872 swr meter that i bought a while back. I just want to set it, erect it, and use it. Mostly base to mobil on ssb. Maybe send the base out for a freq alignment and clarifer mod.

Ok!
Please post your results when it's up & running.

100' of LMR400 will be perfect.

3.25 wavelengths should provide the radio a very broad-banded antenna
- for a metal 5/8 wave

It might not hurt to coat the upper ground radial plates insulator and that same area of the radiator with liquid electrical tape to help keep the SWR down when it rains, and possibly help prevent arcing, if you're not going to replace the insulator

 

[old goat 321]

I am going to address the upper insulator. But instead of using the "Ranch55" approach im going to use a heat shrink tube that insulates up to 600 v. Instead of removing the insulator, im going to overlap it and the radiator with the tubing. Im not sure how long. I could go past the upper standoff but may be over kill. And a copper lube on the joints as others have stated. Thanks for the help and info from you and all of the posts from past and present.

 

[Ranch55]

I am going to address the upper insulator. But instead of using the "Ranch55" approach im going to use a heat shrink tube that insulates up to 600 v. Instead of removing the insulator, im going to overlap it and the radiator with the tubing. Im not sure how long. I could go past the upper standoff but may be over kill. And a copper lube on the joints as others have stated. Thanks for the help and info from you and all of the posts from past and present.

Yes, I originally did exactly as you describe above. It helped a lot, and the SWR's were not affected by the rain anymore......
Until ...... the upper insulator had a hole arced all the way through it right at the horizontal bracket.
That is when I went looking for a better material to make the complete upper insulator all in one piece.
That is why I did what I did. I was chasing and correcting an issue that had already occurred .....
Good luck ......

 

[old goat 321]

Yes, I originally did exactly as you describe above. It helped a lot, and the SWR's were not affected by the rain anymore......
Until ...... the upper insulator had a hole arced all the way through it right at the horizontal bracket.
That is when I went looking for a better material to make the complete upper insulator all in one piece.
That is why I did what I did. I was chasing and correcting an issue that had already occurred .....
Good luck ......

Wow. Were you running a lot of power? Im running a stock radio. If not then i will use your method. Nothing written in stone yet and im in no hurry. Im trying to "get it right the first time ".