I agree LC that the Marconi X6 that I built recently (2009) is maybe a bit more balanced than the original SD'r simply because the Marconi uses all 102" elements and the Starduster is fed a bit off center. Now with this information I can only guess as to the effects on pattern and that there are likely some differences. I
am not able to actually measure the results, but if I could that might suggest some technical differences. When operating purely as a radio operator, I could see no differences with the limited testing I have done recently. More must be done and I may try that this fall.
I consider both antennas to be vertical 1/2 wave dipole antennas, but I would not argue with someone calling them a 1/4 wave ground plane with slanted down GP radials either. Both of these antennas appear to be balanced or somewhat balanced, but I can't define this small physical difference as it might apply to performance. BTW, I did not do Field Strength testing and that may have been a good thing to include. My goals in building the Marconi was to make comparisons as I added GP radials to the antenna and see what affects that it also had on tune and resonance.
For years I figured the purpose of running the coax down the center of the support pipe to be a feed line shielding advantage with the Starduster and still do. The old Avanti Sigma IV also configured a mount that allowed for a sleeved mount as well---so there must be some importance in the idea.
Some years ago (late 80's) a
CB buddy came up with an idea he read in an ARRL article entitled “An Analysis of the Balun” and a discussion of a Bazooka Balun (sleeved). This article can be located on the Internet. His idea was to make the 10’ SD’r mast section a true 1/4 wave length and use a barrel connector and a tuned 1/4 wave jumper from the feed point to the base of the tuned mast where the shield was then directly attached using a hose clamp to a grounded supporting mast or tower. We did not isolate the top of this mast at the hub however, so I'm not sure how much, if any, good this idea really was. But, based simply on my buddies on-air results of reducing his TVI we really believed there were improvements to be made with the idea. I later mounted my own SD’r and discovered while using a mobile Field Strength meter directly below my Starduster antenna---that when
TX'ing the FS meter indicated full scale while my buddies SD'r did not make the meter even budge. Only difference was the modification he made to the mast and feed point connection. We were not aware of any other noticeable differences in performance as both antennas worked exceedingly well---even when compared to other buddies larger and more up-to-date antennas in the Houston area. Back then however we did not really do antenna testing or comparing as a rule. Soon after I modified my SD’r and I saw the same results using the FS meter---regarding the TVI as my buddy did.
Some time later I was made aware of a patent related directly to the ideas we used and maybe even the principles used by the creator of the Starduster antenna back in the early days of
CB radio. You can reference this patent at the US Patent Website see Patent # 2,184,729 which is dated in 1937. Click on:
http://patft.uspto.gov/. So the concerns for destructive radiation on the feed line with a vertical dipole or any vertical antenna with a counterpoise system was evident even back then.
Concerning the over 10’ mast issue in the manual you mention LC, I can’t recall ever seeing a real manual for the SD’r. I could be wrong though, so could you post a link or the text of the manual you referenced?
I’m also not sure how to really determine how or why we need a balun or choke on a verticle, but I hear
CB’rs say all the time that they know exactly what is going on and some are quite categorical about their claims. I’m still waiting for a definitive and convincing answer though.
Concerning isolation of an antenna from the supporting mast. There are many arguments on this issue and I’m still not convinced that I can discuss the issue with confidence. I did conduct a test on one of my A99’s and I did the same when I installed my I-10K. I think I could see some improvement in the performance of my A99, but it was not significant---nothing like my friend Bob95 noted when he insulated an A99 for a neighbor. However, I insulated the brackets from my mast and left the antenna mounted to the side of the mast and not above the mast like Bob85 and Multimode 200 did. So, to be fair that could have made the difference.
At the time I was testing and comparing here, the conditions were mixed with some DX at times and the local conditions varied considerably in my area out to at least 50 miles. I did not try and test with DX rolling, but I did make some observations under those conditions.
At first I tried comparison testing using only one antenna setup using the same mount, line, and radio. When testing I tuned all antennas as best I could to 27.205 mHz. That was just a control measure for me, but in doing so I could notice
RX changes due to changes in tune and for me that was somewhat remarkable and I have never observed that before. I may discuss this later after I have compiled all of my results in my mind and on paper, but in the mean time you can check out what Bob85 has posted regarding similar experiences with his modified Vector 4000 in the past. I refer to that process as a Super Tune, but I'm not sure about how it really applies to performance. You might check the forum for clarification of Bob's work and see what that is all about. Bob85 carried his work well beyond mine with regards to performance in his area of the radio world. I was disappointed of course, but in our discussions on the issue we concluded with the possibility that the very high conductive soil in my area make be mitigating the responses among the different antennas I tested. Had I tested over poor, very poor, or extremently poor soil, I likely would see very different results.
Since I only considered
RX signals as reliable for my work, I make no claims regarding the Super Tune having a positive affect on
TX, but I believe Bob when he tells me of his experiences. So LC, regarding insulation and this Super Tune idea---I still need more convincing and more work. When I do post some of my Signal Reports you can check for what I saw during the hours and hours of testing I did. I have to add Field Strength testing the next time I test.
You have to consider that my work recently was just what it is and nothing more. I use to think that my results had to be similar in all areas, but that is far from correct. Mother nature and Mother Earth exert a profound affect of RF and how and why antennas respond as they do. That might help explain all of the different results we hear all the time.
LC you post: “can we agree that this antenna is in essence a quarter wave vertical dipole and then base our theories off that? if its not, what is it?” Do you mean ½ wave vertical dipole? See above where I discuss this issue.
My thoughts on all ideas of others are---CAN I DUPLICATE THOSE RESULTS AND DO I HAVE ENOUGH INFORMATION TO TRY! In the past it has been almost universally impossible to try, because of a lack of good information regarding process. I attribute much of that to BS ideas unfortunately.
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. im sure at some point marconi will see this thread . i wonder if hed suggest two coax chokes on it , one at the feed point and one 9 feet below , or just one ? 
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