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HY-GAIN SPT 500 PENETRATOR TUNING
- Thread starter barefootindian
- Start date
http://www.worldwidedx.com/cb-antennas/151314-hy-gain-spt-500-penetrator-tuning-2.htm
Hi Booty monster, Thanks for putting the link to CBRADIOMAGAZINE'S review of the Maco v5/8 antenna. Its another way to go for sure, but I will have to see how much it will cost to get one across the pond to me over here. Thanks again Booty.
Hi Booty monster, Thanks for putting the link to CBRADIOMAGAZINE'S review of the Maco v5/8 antenna. Its another way to go for sure, but I will have to see how much it will cost to get one across the pond to me over here. Thanks again Booty.
A small wire running from the center of the SO-239 to the connection hole for the tuning snub. There is no coil in there.
I know this is a old thread but thinking about purchasing a spt 500 if i use the old assembly instructions from the 80s it should be fine to tune to 11 meter i think any info would help guys
JAFO, the PDF file below is an Eznec model I did a while back for the SP500...including my idea for the physical matching device to tune this 5/8 wave antenna.
As you suggest, this model looks to verify that adjusting the top hat angle down for the SP500 using a 271" radiator and 4x1/8"x10" inch Top Hat...does have a modest effect on the tune @ 27.205 mHZ, noted in the Source Data reports.
The model in Free Space indicates a perfect Average Gain value of 0.999=0.00db. The model, over Real Earth, shows a very nice far field gain. This is in spite of having a somewhat skewed radiation pattern...likely due to the mounting bracket used.
As you suggest, this model looks to verify that adjusting the top hat angle down for the SP500 using a 271" radiator and 4x1/8"x10" inch Top Hat...does have a modest effect on the tune @ 27.205 mHZ, noted in the Source Data reports.
The model in Free Space indicates a perfect Average Gain value of 0.999=0.00db. The model, over Real Earth, shows a very nice far field gain. This is in spite of having a somewhat skewed radiation pattern...likely due to the mounting bracket used.
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I've come to prefer a radiator length of 266.7" on all my 5/8
This provides a maximum of .64 at the ceiling frequency of 27.995 and an exact .625 at 27.400
I doubt there's much loss at all at the center of the band 27.185 even though it works out to a .6215 there, and .6165 at Ch.1, shrinking to .594 at the bottom of 11m, 26.000
I'd rather lose a tiny amount of gain at the bottom but keep the radiating angle from elevating above optimum at the top.
Since I spend 98% of my 11m radio time on L38 it works out perfectly.
I'm calculating presuming typical 5/8 construction of:
1.25" bottom, .375" top, radiator diameter as in:
Hy-gain Super Penetrator 500
MFJ SPT-500
Avanti Sigma II
Interceptor 10K, etc.
- and including correction for VF.
This provides a maximum of .64 at the ceiling frequency of 27.995 and an exact .625 at 27.400
I doubt there's much loss at all at the center of the band 27.185 even though it works out to a .6215 there, and .6165 at Ch.1, shrinking to .594 at the bottom of 11m, 26.000
I'd rather lose a tiny amount of gain at the bottom but keep the radiating angle from elevating above optimum at the top.
Since I spend 98% of my 11m radio time on L38 it works out perfectly.
I'm calculating presuming typical 5/8 construction of:
1.25" bottom, .375" top, radiator diameter as in:
Hy-gain Super Penetrator 500
MFJ SPT-500
Avanti Sigma II
Interceptor 10K, etc.
- and including correction for VF.
Thanks for all the info guys i received my antenna monday i used the old penetrator instructions leaving the tophat straight and not at a 45 degree angle and 26 7 dont know if im just lucky or what swr just a tad over 1.1 across the band so far good reports from everyone thanks again
Old thread, but the target Antenna is still available - still valuable info!!
I also frequently use ch 38 (LSB) (27.385 MHz).
Question: Why not tune the antenna for a peak 0.64 wavelength based on Ch 40 (27.405), rather than 27.995 (unless you plan to use the upper freeband)? It seems that way the lower CB channels wouldn't suffer as much, and Ch 38 would have nearly optimum performance. Of course, using any frequency over the tuned 0.64 wavelength would suffer sharply... My goal is simply to maximize ch 38 without having a negative impact on the top two channels, ch 39, 40.
Looking at your calculation, I'm curious where the 266.7" radial length comes from.
Calculating a 5/8 wave for 27.995 MHz, I get a total wavelength of 20.9 feet (250.8").
I truly don't want to challenge your calculations - I'm considering using them, but I want to understand, so I could adjust for the target 27.405 MHz, if you could assist?
I'm currently considering a Hygain SPT-500 Antenna.
Any input would be appreciated.
I don't know what you did with this, but I will tell you that I had an original in 70's & it worked great.