4-BTV Flagpole

[KC9RAK]

After doing a lot of research on this site about the 4-BTV disguised as a flagpole, I'm getting ready to take it on and get it up.  Have a few questions though...

I'm planning to use the DX Engineering radial plate.  Any reason this can't be covered with mulch to hide it?  I'm thinking about a little landscaped area of river rock and mulch with the flagpole in the middle along with plants and flowers... gotta keep the wife happy  .  I don't think the radials being partly under river rock or mulch should affect it.

The other thing I'm contemplating is how to tune it.  Don't want anyone to see it's not really a flag pole.  Might have to do my tuning under the cover of darkness and then when it's done, the PVC flagpole goes over it.

Thanks!

Dave

[G7MRV]

I'd be interested to see how you get on with this. Ive just put up a 25ft flagpole on my sons wooden play fort, with the express intention of eventually having a vertical antenna within it. (hes been wanting a flag pole anyway). Im using the tactic of installing the pole first, then leaving it a few months for the neighbours to get used to it/complain, before making it an antenna.

Curiously though, this flag pole was an antenna! Or rather, was two!. Its made from the fibreglass tubes of two industrial low VHF collinear antennas, one slotted over the other by a few feet!

[W8JX]

I would use the 6BTV for this as it will give you two more bands and no spider to remove. On radials and radial plate you will get a LOT of feed back on this of different views. Some will tell you you need 40 or more radials and some far less to to well. I have been using a "backup" 5BTV for many years that has no radials at all. Only ground it has is a 7 foot fence pole driven 6 feet in ground that antenna is bolted too. It any case radial on on in ground do not need to be resonant so put out 6 or eight and hide them with landscape staples and simply attach them to a metal pole that antenna should be mounted on.

[N4UM]

Instead of using mulch to cover up the radial plate and radials in the vicinity of the "flag pole,"consider using a "tree ring" available from Lowe's or Home Depot.  I use one that is made from recycled rubber tires (I think).  It's 36" in diameter and about an inch thick.  You don't have to worry about weeds or grass growing through it.  I installed mine and use an inverted plastic flower pot with a hole drilled in it's center over the base of the pole to conceal the feedpoint.  I've place landscaping bricks in a circle on the outer edge of the tree ring. It make for a neat installation and I don't have to worry about mulch floating away in heavy rains etc.

[KC9RAK]

Thanks for the replies!  I'll check out the tree ring.  And now I'm considering the 6-BTV.  Will have to do a little more research on that but it looks to be 25 feet.  So perhaps a 26+ foot flag pole?  I checked our covenants and their is nothing in there against flag poles and many houses on my street have one.  Mostly made out of aluminum though. 

I've read the flagpole article in DX Engineering for the BTV antennas and wondered if 2 inch thin wall PVC would be stout enough up 25 feet.  Any thoughts on that? 

Dave

[WX7G]

PVC pipe will offer no mechanical support and due to it increasing the surface area of the antenna it will decrease the wind survival of the antenna. But if it does blow over will it harm anything other than itself?

The weak point on the BTV verticals is the first 6' tube. It's 1.25" O.D. and can be strengthened by slipping a 1.375" O.D. 6' tube over it. I use the 6' slotted tube from DX Engineering.

To avoid tuning it up - adjusting the lengths of the sections - you can set the dimensions per the BTV assembly manual and touch up the match at the shack using a tuner.

[KC9RAK]

WX7G, Thank you for the reply!!  I am planning to run it through my MFJ-993B tuner in the shack so perhaps I will just set it per spec.  Would like to tune it though but don't want to risk having it discovered as an antenna.  Will have to think about that. 

I'm trying to visualize a 2 inch wide flagpole up 25+ feet from an aesthetics perspective.  I was thinking that a wider pipe would look better but you're probably right... would just increase the wind load.

Interesting on the tube you're sliding over the first 6".  Would DX Engineering understand the part you're describing if I called them up?

Thanks again!!

Dave

[AC4RD]

Interesting on the tube you're sliding over the first 6".  Would DX Engineering understand the part you're describing if I called them up?

I've never asked them that particular question (my own vertical is homebrewed), but in general, you can call or email DX Engineering and get a great honest useful answer from someone who actually knows what he's talking about.   "Customer service" is disappearing fast from other areas of retail, but the guys at DXE are great.  (IMHO.)

[WX7G]

The part number for the 6' length of 1.375" tubing is: DXE-AT-1212

I just measured a BTV trap and the maximum diameter is a hair under 2.0 inches. Whatever plastic tubing you put over the BTV vertical will need to have an I.D. of 2.0 inches or larger.

[K5LXP]

I am planning to run it through my MFJ-993B tuner in the shack

Not a great idea in terms of efficiency, and not all that convenient to operate either.  You have an antenna that can operate multiple bands without a tuner and with decent efficiency.  Why compromise that?


Mark K5LXP
Albuquerque, NM

[KC9RAK]

Mark, I really don't want to run it through the tuner... Just trying to evaluate how I will be able to tune it in the open without neighbors discovering what it really is.  All they can be allowed to see is a fiberglass flagpole.  Might be midnight ops!

I've been going back and forth between the 4-BTV and the 6-BTV.  I'm concerned about the wind loading on the 6-BTV with the PVC because I won't be able to guy it.  I'm really not on 80 meters now but you never know about the future.  How will 40 meters be on the 4-BTV without the capacitance hat?

Thanks for the replies so far!!

Dave

[W8JX]

How about just getting a proper flag pole antenna from zero five or something?

[KU7I]

A Navy friend of mine put up a 24 foot flag pole antenna. I think it might be from Zero Five or maybe Force 12, I do not remember but he runs an Icom AH-4 remote tuner at the base. The thing is a flame thrower 10 to 40 meters. He does not have much interest in the low bands so I can not comment on those
He has a pretty small yard in Navy housing...I think his back yard is around 20 feet wide by 40 feet long so not that big at all but what he DOES have is a great ground plane. He has 100 ten foot radials and another 40 or so that are 20 feet long and bent here and there to fit. I might do something similar here in Japan when my JA license arrives.

Lane
Ku7i
Yokouska US Naval Hospital
no JA call yet

[KG4RUL]

When you encase the 4-BTV in a piece of PVC pipe, the factory recommended dimensions for tuning will change.  You will need the tuner unless, and it seems this will not be the case, you can erect and take-down the antenna multiple times to get the adjustments correct.

[WX7G]

RUL is correct. Midnight tuning is in order. Or perhaps you can set up the antenna in a field somewhere with a similar ground system and tune it there.

The 4BTV can be converted to a 5BTV by adding the RM-80 resonator. The RM-80S is too fat to fit in a 2" tube and the RM-80 works just fine. The 80 meter band 2:1 VSWR bandwidth is 40-50 kHz. The 4BTV will work on 30 meters using a tuner in the shack. There will of course be considerable loss in the coax but you will still make contacts.