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BBT Delivered Hy-Gain Penetrator 500 Today
- Thread starter Eastside
- Start date
It is after my amp (Cobra xl350) then the isolator and out to the antenna. I am thinking of making the antenna a hair shorter because at 27.605 with the amp at med. power or with out the amp the swr's are 1.0 to 1.1. I mainly work 28.3 to 28.5 and with the amp at med or high I see 1.7 to 1.8, without the amp about 1.3 to 1.4. Wish I had a tuner but can't afford one at this time. What puzzles me is with my big stick amp or not I never saw a swr reading above 1.5 from 11 to 10 meters. Maybe because the big stick had a matching coil and the sp500 does not. I do not understand antenna theory.
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BOOTY MONSTER
Guest
do you know that more power does not change the tuning of a antenna , unless it damages the antenna ?
Yes more power should not change the swr reading, I do not understand what is going on but it does seem to be doing it with this antenna. The only thing that has changed is the antenna and it was pretty easy and straight forward to install. It is not very high and the radials are just a few feet above the roof and my carport and garage. I did raise it up about 5 more feet but did not make any difference so I lowered it back to be shorter than the tree close by. Maybe lightning would hit the tree first before my antenna. I did ground the mast at the base with a ground rod. I am not sure what to try now, the ham guys say end fed verticals are prone to issues and must be a installation problem or poor antenna design. I should add my power supplies are not grounded as my home only has 2 wire ac outlets but this should only be a safety issue with shock hazards.
The Hy-gain Penetrator is not an "end-fed" antenna, it is an inductively matched antenna. An end-fed is the common half-wave antenna. End-fed's don't need radials, but a 5/8ths does.
I somehow suspect that line isolator is somehow affecting the VSWR as it heats up. How many watts is it rated for? That Cobra XL350 shouldn't put out more than about 250W, if I'm not mistaken?
most half waves are inductively matched too, with the bottom end of the coil being dc grounded and the coil being tapped at the 50 ohm point, same as 5/8 wave's
End fed's without radials will have all sorts of cmc problems. Which is exactly why antennas like the A99 SUCK.
if you were to truly end feed a half wave you would have a vswr in the region of 20.0 :1 when using coax as the feedline.
The isolator is rated for 1500 watts pep but not recomended for am or continous duty. Of course when checking swr you have to use am or fm, I don't leave it keyed up for long. The swr's only increase about .5 with power so I am not sure if that is a problem. The isolator does help with making the antenna more broad banded. I am not sure what to try next or if I need to try something other than maybe shortening the antenna to get the sweet spot closer to 28.3 mghz. I almost wish now I would have went with the Cushcraft ar10 ringo. I figured the 5/8 wave would out perform the 1/2 wave but did not expect issues.
Absolutely true. I failed to mention that. You need that "transformer" to match the relatively hi-Z (about 200 - 400 ohms) to the 50 ohm coax.
I couldn't agree more. Apart from relatively poor RX sensitivity (same gain as a 1/2 wave dipole, which essentially it is). That extra 1.2 dB gain that a 5/8ths exhibits makes all the difference, not to mention the lower TOA.
Hmmm...that implies a Z of around 1000 ohms... that high you think?... Hmmmm.... maybe....
Hmmmm... I don't understand your problems. When I took my original Penetrator and simply shortened it, it worked perfectly on 28.800. No issues, no VSWR, nothing! Of course it was up on a 25' pole above the roof. Maybe it's proximity to other structures?
I guess I thought it would be more broad banded than it is. It does work better with the isolator and that makes me think of coax issues maybe. The coax is 10 years old and last couple of winters have been harsh not to mention the heat this year. I will probably shorten it a bit to get it resonat at 28.3 and not the 27.6 it is now. I still do not understand the slight swr increase with power but it could be the proximity of the house, trees etc. I really don't have a clear path to put it any were else. Power lines and phone cables etc limit my locations and it is real close to the radio room maybe 8 feet away. It is no higher up than the big stick I was using but like I said before the radials are not very far above the house, carport garage etc. Most of the rf should be above the radials but like I said I do not understand antenna theroy.
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BOOTY MONSTER
Guest
TVRC18, here is an overlay of patterns for an End Fed .50wave, versus a simulation model of the I-10K, and another model I have for a .625wave vertical, all at 40' feet elevation. You will note that there is hardly any difference in angle or gain among these Eznec5 models. I believe you would likely do just about as good and maybe even a little better using your Big Stick...under the height and location conditions you site.
Those big radials, in the case of the SP500, may be attenuating your antennas performance being so close to the building.
View attachment .50 wave vs, .625 wave.pdf
My big stick is getting old but it still does pretty good. I was looking at the ringo 10 by cushcraft. I started to buy one before the sp500 but they back ordered it. I remember now about 10 years ago I tried the Maco v58 and had similar problems. My memory is getting bad I guess and had forgotten about that.
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