From what I have read from the early 1975 spt-500 manual that was advertized for 11 meter. Radiator should be 22' 9.5" long and the ground plane radials should be the normal 105" or 8' 9" long. That is where im setting mine at and i bet that will be right on for 11 meters.
1970, if you have an old 500, according to the manuals, they were set at 273" and that was probably the length when 23 channels was the thing. I think later they reset the length to about 270" for the new 40 channel radios. It looks like that were several versions over the years with a different base length ranging from 71" to 77" inches too. The exposed tips for all the old manuals I have show to be 50" inches, while the lengths of elements M2 to the tip range from 193.125" to 196" to 199.125" inches, and these differences tend to make the base element vary also as noted above.
I think the base for the New SP 500's is 72" inches, and the exposed length for the top element is shorter than in the past too. The total length is the shortest length that I have in the manuals I have...at about 264" for 27.205 mhz.
There are probably a lot of combinations for different element lengths that can be used and give similar results. If the antenna is tuned right, my Eznec models with the matcher added...suggest this antenna will make a very good match at both 10 and 11 meters. This matching device looks to be very broad banded, and that surprised me. However, if the bandwidth changes much, when tuned to the outer limits...this might suggest the matcher can produce more losses.
The New SP 500 might also tune to 12 meters, but it looks to me to be short of having enough material to reach. At 24.950 mhz, I figure the physical antenna is about 6" short of having enough material to reach resonance, but that is just an estimate.
VA3ES, my comments are directed to my attempts to model the SP 500 using Eznec, and including a matching device that will result in this antenna showing a good match, and responding to changes in frequency if I wanted to re tune the antenna. I do not have the specifics for the dimensions of the beta matching device and therefore the model might be showing less than stellar performance. I didn't expect to see that, base in part on such good reports, like your's, over the years.
I posted models and said they did not look good or as I would expect, but I was trying to drum up some interest so that maybe someone would take the time to accurately measure their New SP 500. I've asked repeatedly for this information, but few have ever come forward. I just figured nobody cared what Eznec might show and I could not make anyone have some interest in order to possibly see what modeling might show for this antenna. Is it different like many claim or is it just like any other 5/8 wave radiator.
VA3ES, you note that HyGain made some change to the beta matcher for their New SP 500, right? I don't doubt it, but I did not notice that in what I've see posted here on WWDX. Can you clue me in on what you see as being different? If you have all the dimenions I need to try and get my model to working better, could you share that with me. Maybe these differences will do what I expect and the model will start to produce the results I was looking for.
I realize most guys on these forums don't know "sick em' from com-e'er" about anything regarding modeling...and I sometimes wonder why I even bother too.
If you can help me, then thank's much.
