Stacking 4' mast and S/D ant. PROBLEMS!!

[hammer0630]

I purchased new military surplus antenna masts or just the same stuff sold to the military and the public. It comes in 4' sections and is aluminum and stacks as high as you wish to go and mine was advertised as 1.75 OD for my newly purchased Starduster antenna. Not knowing for the S/D that the mast is much more than a pole that holds up a antenna rather that is a integral part of the antenna. The mast is made very well and each section weighs exactly 2 pounds but these are the two problems I have encountered first the mast sections are multi ribbed on the outside giving a larger diameter than stated since they are stackable the upper ends are tapered about 4 to 5 inches in length "smaller diameter" allowing the next section to slide over each other and inter lock. This tapered section which is perfect for the S/D's top section hard ware which sits directly on top of the mast and held in place with 2 set screws "this is where the coax screws to the antenna" with three threaded fittings for the three downward radials and also threaded for the top section of around ten feet of the upper most part of the antenna fits perfect but then several feet from the top mount is another section of the S/D hardware that mounts another bracket that insulates and supports the three two piece downward radials "about ten feet in length" this section of the antenna's hardware which is a bored out of solid aluminum round machined circle with three plastic arms that was designed to slide down the mast to the desired manufacturers length and secure the three downward elements at the proper angle from the mast itself but will not fit my mast which is just slightly to large in diameter. Now I am trying to figure out how do I get this radial support to fit which is about three feet from the S/D top section which is also the top section of the 4' mast. Well finally I came up with cutting off the top mast bottom section about 16" to conform to the manufacturers measurements and distance between the two installation brackets and by using another 4' mast tapered top section and fitting the round radial support bracket in between the two stackable masts this then will allow the non conductive round radial mount to slide on perfectly and tightening the radial brackets set screws in between the two mast sections together and drilling two holes and riveting the two masts together. Also these stacking mast poles do not wedge together and spin easily and even slightly wobble so I have drilled and riveted all six stacking poles for a total length of 24'. Because of absolutely no other way of installing the antenna on my roof I have had to use an eave mount and since the coax runs through the antenna mast the bottom section of the eave mount will not allow the coax to exit the mast "sits on heavy galvanized angle iron steel type bracket with U bolt or muffler clamp for securing mast" so several inches from the bottom mast in between the top and bottom antenna eave brackets I have had to cut a rectangular hole to allow the coax to be able to exit the mast and allowing a gradual 45 degree angle to slowly curve as to not create a reflection or bottle necking "SWR PROBLEMS" and continue on to my radio. Having to cut an exit hole in the mast for the coax I am hoping this hole has not greatly affected the strength of the mast. Since this cut out section is between the upper and lower sections of the eave brackets this is probably the least stressed area of the mast in windy conditions. These stacking masts are very well made but not very well engineered I don't think it will pose a great problem. I wrote this article in case anyone is interested in the aluminum stacking masts as they just merely sit on top of each other and can spin etc gravity is the only thing keeping them together and especially if you are installing a Star Duster antenna to this type of mast and have to use a eave mount I would give great thought of trying a different way. Even with a solid mast pipe you would still have a problem with the coax exiting the lower eave mount. I have to admit though this is now one very impressive looking antenna set up the Star Duster looks like a rocket ship sitting on a launch pad ready for take off and no visible antenna wire does give it a clean look and my AntennaCraft ST-2 scanner antenna if you are familiar with this mounts off the antenna mast at a 45 degree angle and then sits upright with 6' above and below it's mounting mast has the regular people thinking I am N.A.S.A. or something over here. I would love to have sent pictures of this but the site keeps telling me I have to many pixels and need to reduce the count. I have tried and tried to do this but no luck.

 

[Marconi]

0630, if you read the mounting section in the Avanti manual for their Sigma IV, you will see that Avanti claimed the antenna was designed to be side mounted...using hardware that use to be provided in the kits. The same information is also in the Sigma IV design made by Antenna Specialists later on.

http://www.cbtricks.com/ant_manuals/avanti/av174/graphics/sigma4_av174_om.pdf

You'll note that this idea is similar to the Starduster idea of running the coax down through a section of mast, which in the case with the SD'r is due to the SD'r design. With the SD'r design one has to run the coax down inside of the mast.

I use to wonder why Avanti made the claim that their S4 was designed to use this type of mount too. I talked to a friend with a handle of Nemrod, a radio buddy, back in the early 90's. He was a serious type, and I am curious and liked talking about antennas with him. So, this subject all got started with me when I asked him what he though might have been the reason Avanti used this common idea on their S4, and also said the antenna was designed to be mounted that same way. We had a lot of discussions as a result of that question I posed that day.

It so happened Nemrod had a neighbor that worked for a big electronics company, and he told us that Avanti presented them with a demo of the S4, and gave a technical talk about the design as part of a technical conference tour Avanti was doing about that time.

The short of this story is...that this S4 mounting design was related to an idea of a third conductor on the feed line when using unbalanced coax. The idea was a choking idea that was referred to as a "bazooka" balun in many articles of the time.

Here is an article on that subject that Nemrod found: http://www.arrl.org/files/file/Technology/tis/info/pdf/8004019.pdf

IMO the side mounted idea can have a unique function, and is a bit more specific than I think you're suggesting here, but I'm not trashing your idea.

Good post hammer0630.

If this makes any sense...how say you?

 

[hotrod]

I purchased new military surplus antenna masts or just the same stuff sold to the military and the public. It comes in 4' sections and is aluminum and stacks as high as you wish to go and mine was advertised as 1.75 OD for my newly purchased Starduster antenna. Not knowing for the S/D that the mast is much more than a pole that holds up a antenna rather that is a integral part of the antenna. The mast is made very well and each section weighs exactly 2 pounds but these are the two problems I have encountered first the mast sections are multi ribbed on the outside giving a larger diameter than stated since they are stackable the upper ends are tapered about 4 to 5 inches in length "smaller diameter" allowing the next section to slide over each other and inter lock. This tapered section which is perfect for the S/D's top section hard ware which sits directly on top of the mast and held in place with 2 set screws "this is where the coax screws to the antenna" with three threaded fittings for the three downward radials and also threaded for the top section of around ten feet of the upper most part of the antenna fits perfect but then several feet from the top mount is another section of the S/D hardware that mounts another bracket that insulates and supports the three two piece downward radials "about ten feet in length" this section of the antenna's hardware which is a bored out of solid aluminum round machined circle with three plastic arms that was designed to slide down the mast to the desired manufacturers length and secure the three downward elements at the proper angle from the mast itself but will not fit my mast which is just slightly to large in diameter. Now I am trying to figure out how do I get this radial support to fit which is about three feet from the S/D top section which is the top section of the 4' mast. Well finally I came up with cutting off the top mast bottom section about 16" to conform to the manufacturers measurements and distance between the two installation brackets and by using another 4' mast tapered top section and fitting the round radial support bracket in between the two stackable masts this then will allow the non conductive round radial mount to slide on perfectly and tightening the radial brackets set screws in between the two mast sections together and drilling two holes and riveting the two masts together. Also these stacking mast poles do not wedge together and spin easily and even slightly wobble so I have drilled and riveted all six stacking poles for a total length of 24'. Because of absolutely no other way of installing the antenna on my roof I have had to use an eave mount and since the coax runs through the antenna mast the bottom section of the eave mount will not allow the coax to exit the mast " sits on HD L angle steel type bracket" so several inches from the bottom mast in between the top and bottom antenna eave brackets I have had to cut a rectangular hole to allow the coax to be able to exit the mast and allowing a gradual 45 degree angle to slowly curve as to not create a reflection or bottle necking "SWR PROBLEMS" and continue on to my radio. Having to cut an exit hole in the mast for the coax I am hoping this hole has not greatly affected the strength of the mast. These stacking masts are very well made and I don't think it will pose a great problem. I wrote this article in case anyone is interested in the aluminum stacking masts as they just merely sit on top of each other and can spin etc gravity is the only thing keeping them together and especially if you are installing a Star Duster antenna to this type of mast and have to use a eave mount I would give great thought of trying a different way. Even with a solid mast pipe you would still have a problem with the coax exiting the lower eave mount. I have to admit though this is now one very impressive looking antenna set up the Star Duster looks like a rocket ship and no visible antenna wire does give it a clean look and my AntennaCraft ST-2 scanner antenna the way it mounts off ant mast or tower at a 45 degree angle has the regular people thinking I am N.A.S.A. or something over here. I would love to have sent pictures of this but the site keeps telling me I have to many pixels and need to reduce the count. I have tried and tried to do this but no luck.

is your s/d made by sirio??? not sure exactly whats going on. ive read it all and probaly
forgot most of it .lol. but i thought you said you cut the antenna?????bad. try getting
a random lenth of METAL pipe we,ll say 10 feet. mount your s/d to the top of it
run your coax thru that pipe onlly . then mount that to the allumin pipes using c-clamps
like a a99 uses. radio shack has them .think ive seen them at walmart tioo

 

[hammer0630]

is your s/d made by sirio??? not sure exactly whats going on. ive read it all and probaly
forgot most of it .lol. but i thought you said you cut the antenna?????bad. try getting
a random lenth of METAL pipe we,ll say 10 feet. mount your s/d to the top of it
run your coax thru that pipe onlly . then mount that to the allumin pipes using c-clamps
like a a99 uses. radio shack has them .think ive seen them at walmart tioo

No, I figured a way to get the mast sections to work with the antenna. I cut one of the 4 'mast section to accommodate the Star Duster. I really need pictures to make sense of this long winded article I wrote. The just of my story is there can be a lot more that could go wrong with an antenna that relies on a mast to be a antenna and most antenna mounting and accessories are not intended for the coax running through the mast and the military stacking mast do not fit tight with each other and that could be a problem for many antenna's and I had to use rivets to secure each section of stackable mast sections and since the coax runs through the mast you have to keep the inside of the mast unobstructed "don't use screws etc" And mostly because of my hard headedness thinking this is what I bought it for and I'm gonna make it work rather than this won't work just buy what you now know you need! Maybe I have to many tools egging me on lol.

 

[Marconi]

0630, I've used this 4' military tubing too and I bolted the sections together, but I attached the antenna to the side if I planned to run the coax through a section of tubing to help create a balun effect for the feed line. I installed an A99 in a 70' foot pine tree using about 20' feed of this tubing and I mounted the antenna to the side of a 1" pipe I also screwed into this heavy wall tubing.

One of the keys to this bazooka balun idea working is that the feed line connector needs to be inside of the top of the tubing. This is where the rf starts to radiate. And, to be sure, at the bottom end of this 1/4 wave tube the coax shield needs to be directly grounded to the mast below. So if the length to diameter ratio for the tubing correctly makes a resonant 1/4 wavelength at the bottom the voltage should be very high and thus stop the common mode currents from flowing down the rest of the feed line.

On the Starduster I use a tuned 1/4 wave jumper from the feed point down, and add a barrel connector at the bottom to connect the working feed line. I cut the bottom of the 1" pipe just short enough so the barell connector sticks out so I can use a hose clamp to ground the shield to the mast...as it exits the bottom of the bazooka. This works for me.

Just make sure to seal the barrell connector well from water getting into the feed line. The SDr's design can and will allow water to drain right into the connector, straight into the feed line.

I also drill a very small hole near the bottom of the radiator to let water drain out, and this works well too. I also use a teflon type paste like product inside of all of my connectors that are installed outside, which is labeled "Stuf." It is available from www.aesham.com

I also like to set my SD at 42' feet high. Be sure to secure you feed line from suffering from the hanging weight of your feed line...or else the coax connector and line will suffer from the constant wind and weather.

I'm still using one of my original SDr's that I bought in the 80's and it has never failed me.

Good luck.