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SPT-500 VS Imax with GP kit

IDIeselman

IDIeselman

Active Member
Oct 20, 2010
260
38
38
53
Lake Michigan
Well gentlemen, lets have it. I have been reading for two days on the merits of each antenna and have read countless "tests" of each, of all the antennas tested against the Imax not one included the GP kit on the Imax. I understand they are both 5/8 wave antennas but has anyone actually tested the SPT-500 against the Imax with enough results to sway the purchase to one over the other? As you may have guesssed, I installed the 2000/GP kit a couple weeks ago and while I am happy with it I just can not leave well enough alone. I have a city dwelling friend that wants my Imax and is willing to buy me the SPT-500 in trade for the Imax and me helping him set it up. Would you make the deal??
 

i think if i had $150 to put into a antenna , id like to try the gain master for $30 more . i hear that kool-aid is really good . you will need a physically strong antenna for the lake michigan area .
 
Booty, are you being facetious or would you honestly rather have the Gain master over the PT-500? I actually do not think the difference between the three mentioned would be worth taking one down and putting two up, sadly I do not yet know enough about antennas to know if my thoughts are near correct. I have the opportunity to try another antenna at no more cost than taking them down, if there was an honest ugrade to be gained I would do it.
 
IDIeselman said:
Booty, are you being facetious or would you honestly rather have the Gain master over the PT-500? I actually do not think the difference between the three mentioned would be worth taking one down and putting two up, sadly I do not yet know enough about antennas to know if my thoughts are near correct. I have the opportunity to try another antenna at no more cost than taking them down, if there was an honest ugrade to be gained I would do it.
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ive never had , used or actually seen a gain master , i had a P500 as a teen and it kicked butt . according to the kool-aid/reports of many actual users it seems to be as effective as any other 5/8 , but , it has a very wide usable bandwidth , very easy assembly and and no horizontal or sloped ground elements to contend with . besides , i can build a p500 , but i don't know how to build a gainmaster .
 
I don't think there is any real contest between the Imax and the SP. Both have vertical radiators that are 5/8 of a wavelength long. The REAL difference between those two antennas is in the matching section. Advantage goes to the SP because it used a 'trombone' or 'beta match' which has less db loss than the Imax does with its dual matching coils and broad banding capacitor. But while the SP may have a slight advantage over the Imax does for 11m; the Imax can be used on a few Ham bands AND 11m to boot. You can't say that about the SP.

But if you are just going to do 11m/CB band only and want the best for that; then any 5/8 wave ground plane antenna that has a low loss matching device and should be fairly equal. Like the Maco V-58 and the SP. Not much loss or gain advantage when comparing those two antennas - as an example. Because the Imax is broad banded it loses some with that making it compromise 11m/CB performance. Keep in mind that we are only talking about the difference of a few db's or so. Maybe more. Takes 6 db's of loss to equal one S-unit - BTW . . .

The Sirio Gain Master is a unique design if you compare it to all of the other commercial offerings. Has less db loss than an Imax does and probably the same loss as the SP. Then again; the SGM doesn't have the same usable bandwidth as the Imax does either. Apples and oranges. But what is a few db's of loss between friends? With the small loss of the Imax loses to the other two antennas - it makes up for it with its broad band ability - if you use it for Ham bands as well . . .
 
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p-500 anyday .
imax for me was just a long flimpsy rfi nightmare. and the the gpk well
the radials are too short to really help the antenna.although 102 whips
mounted on the gpk that would be more helpful imho.nex is the lousy
matching setup as already mentioned.as for the gainmaster cant say never had
one .some like it others dont.
 
p-500 anyday .
imax for me was just a long flimpsy rfi nightmare. and the the gpk well
the radials are too short to really help the antenna.although 102 whips
mounted on the gpk that would be more helpful imho.nex is the lousy
matching setup as already mentioned.as for the gainmaster cant say never had
one .some like it others dont.
 
I've had all 3 and the Sirio Gainmaster is the best overall performer and is about as wide banded as the Imax was after I added 25' wire radials to the Imax. The SP500 beat the Imax by about a full s unit and the Gainmaster beat the SP500 by about what they say, 1.5-2db.
They were all tested with the same height mast coax radio and stations. I especially like the lack of radials on the Gainmaster. It just makes for a neater appearance and less wind loading.
Another thing about the SP500 vs the Imax, the Imax is 1-2 s units noisier than the SP500. When I usually got s3-s4 of noise on the Imax the SP500 was s1-s2 and I could hear the weak stations much more clearly on the SP500. Some were even lost in the noise on the Imax who I could hear well on the SP500.
I think the Gainmaster needs to be installed well above and away from any metal, even uninsulated guy wire or it won't perform as well, which makes the SP500 more installation-friendly and versatile.
If you get the SP500 I think you will need to make it 22' 8" from the bottom connector to the top screw holding the top hat to tune it for center of band, 27.2mhz. That is what mine measured for lowest reactance and SWR with 8' 9" radials.
For ch38 I shortened it to 22' 6" with 8' 8" radials.

:)
 
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Needle Bender said:
I've had all 3 and the Sirio Gainmaster is the best overall performer and is about as wide banded as the Imax was after I added 25' wire radials to the Imax. The SP500 beat the Imax by about a full s unit and the Gainmaster beat the SP500 by about what they say, 1.5-2db.
They were all tested with the same height mast coax radio and stations. I especially like the lack of radials on the Gainmaster. It just makes for a neater appearance and less wind loading.
Another thing about the SP500 vs the Imax, the Imax is 1-2 s units noisier than the SP500. When I usually got s3-s4 of noise on the Imax the SP500 was s1-s2 and I could hear the weak stations much more clearly on the SP500. Some were even lost in the noise on the Imax who I could hear well on the SP500.
I think the Gainmaster needs to be installed well above and away from any metal, even uninsulated guy wire or it won't perform as well, which makes the SP500 more installation-friendly and versatile.
If you get the SP500 I think you will need to make it 22' 8" from the bottom connector to the top screw holding the top hat to tune it for center of band, 27.2mhz. That is what mine measured for lowest reactance and SWR with 8' 9" radials.
For ch38 I shortened it to 22' 6" with 8' 8" radials.

:)
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excellent report needlebender.and results is what id think they would be. my only question
is how is the floor noise level compare on the GM vs the imax? being both fiberglass
and two how does floor noise level compare against the GM vs the p-500
 

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