4-bay Using Metal Tubes Instead Of Bowties

[ota_canuck]

Being that this tubing is quite large with open ends, I'd be interesting to hear this antenna singing during a wind storm. Eight whistles ,.. so maybe some thoughts on closing the ends of the tubes should be considered. Would simply squishing the ends closed effect the performance?

[BOUVAL]

Eight whistles

That I know, it's not intended to be a permanent install.

I can glue some quarters on the open ends with the queen's face facing in.
.

[300ohm]

Because of the use of 1 inch tubing with 14 ga phasing lines, the NEC program engine is kicking out a lot of Errors and Warnings about that large disparity in sizes. Also, in order to adjust AGT, I had to use a segment size of 5, which decreases accuracy. So I would say the gain figures are probably overstated. However, the relative trend shown is useful.



As is, the antenna is peaking at 812 mhz. Channel 51 goes up to only 698 mhz and channel 69 only went up to 806 mhz. Without a reflector, the peak is at 830 mhz. So it does show that the tubes need to be longer. 9 inches would have the antenna peak at 698 mhz, and the bay spacing would also have to be increased. Also the short reflector to driven element distance is increasing the SWR significantly.

NEC file:

CM Bovals 1inch Fat Dipole 4 bay
CM AGT = 1.0 (0db) at 585mhz, Autoseg = 5
CM Lots of NEC Errors and Warnings due to 1 inch dipole and 14 ga phasing lines
CE
GW	24	1	2.875	-0.875	10.5	2.875	-0.875	9	0.0321
GW	25	1	2.875	0.875	10.5	2.875	0.875	9	0.0321
GW	26	3	2.875	-0.875	7	2.875	-0.875	3.5	0.0321
GW	27	3	2.875	0.875	7	2.875	0.875	3.5	0.0321
GW	28	1	2.875	0.875	7	3.275	1.0927e-15	8	0.0321
GW	29	1	2.875	-0.875	9	3.275	1.0927e-15	8	0.0321
GW	30	1	2.875	-0.875	7	2.475	1.0927e-15	8	0.0321
GW	31	1	2.875	0.875	9	2.475	1.0927e-15	8	0.0321
GW	32	1	2.875	-0.875	-10.5	2.875	-0.875	-9	0.0321
GW	33	1	2.875	0.875	-10.5	2.875	0.875	-9	0.0321
GW	34	3	2.875	-0.875	-7	2.875	-0.875	-3.5	0.0321
GW	35	3	2.875	0.875	-7	2.875	0.875	-3.5	0.0321
GW	36	1	2.875	0.875	-7	3.275	1.0927e-15	-8	0.0321
GW	37	1	2.875	-0.875	-9	3.275	1.0927e-15	-8	0.0321
GW	38	1	2.875	-0.875	-7	2.475	1.0927e-15	-8	0.0321
GW	39	1	2.875	0.875	-9	2.475	1.0927e-15	-8	0.0321
GW	40	3	2.875	-0.875	3.5	2.875	-0.875	0	0.0321
GW	41	3	2.875	0.875	3.5	2.875	0.875	0	0.0321
GW	42	3	2.875	-0.875	-3.5	2.875	-0.875	0	0.0321
GW	43	3	2.875	0.875	-3.5	2.875	0.875	0	0.0321
GW	813	1	2.875	-0.875	0	2.875	0.875	0	0.475
GW	814	3	2.875	0.875	10.5	2.875	7.875	10.5	0.5
GW	815	3	2.875	-0.875	-3.5	2.875	-7.875	-3.5	0.5
GW	816	3	2.875	0.875	3.5	2.875	7.875	3.5	0.5
GW	817	3	2.875	-0.875	3.5	2.875	-7.875	3.5	0.5
GW	818	3	2.875	0.875	-3.5	2.875	7.875	-3.5	0.5
GW	819	3	2.875	-0.875	10.5	2.875	-7.875	10.5	0.5
GW	820	3	2.875	-0.875	-10.5	2.875	-7.875	-10.5	0.5
GW	821	3	2.875	0.875	-10.5	2.875	7.875	-10.5	0.5
GW	822	11	0	-10	0	0	10	0	0.1875
GW	823	11	0	-10	1.875	0	10	1.875	0.125
GW	824	11	0	-10	3.75	0	10	3.75	0.125
GW	825	11	0	-10	5.625	0	10	5.625	0.125
GW	826	11	0	-10	7.5	0	10	7.5	0.125
GW	827	11	0	-10	9.375	0	10	9.375	0.125
GW	828	11	0	-10	11.25	0	10	11.25	0.125
GW	829	11	0	-10	13.125	0	10	13.125	0.125
GW	830	11	0	-10	15	0	10	15	0.125
GW	831	11	0	-10	16.875	0	10	16.875	0.1875
GW	832	11	0	-9.975	-16.875	0	10.025	-16.875	0.1875
GW	833	11	0	-9.975	-15	0	10.025	-15	0.125
GW	834	11	0	-9.975	-13.125	0	10.025	-13.125	0.125
GW	835	11	0	-9.975	-11.25	0	10.025	-11.25	0.125
GW	836	11	0	-9.975	-9.375	0	10.025	-9.375	0.125
GW	837	11	0	-9.975	-7.5	0	10.025	-7.5	0.125
GW	838	11	0	-9.975	-5.625	0	10.025	-5.625	0.125
GW	839	11	0	-9.975	-3.75	0	10.025	-3.75	0.125
GW	840	11	0	-9.975	-1.875	0	10.025	-1.875	0.125
GS	0	0	0.0254		' All in in.
GE	0
EK
LD	5	0	0	0	1.66667e7	0
EX	0	813	1	0	1	0
GN	-1
FR	0	1	0	0	585	0

[BOUVAL]

I'd like to give it a try, so I have 2 lengths of 29.5" AL tube 7/8" O.D. I can cut them to 29"

Those tubes being that big, should I put them farther than half an inch from the top and bottom elements ?

Thank you 300ohm for the modeling, but I don't believe in going longer with the elements. One thing that I'll try though is increasing the ref/ele spacing by an extra 2 inches.
.

[300ohm]

Those tubes being that big, should I put them farther than half an inch from the top and bottom elements ?

Probably yes, Ill have to model it later. I wouldn't cut the tubes, at least not yet, that .5 inch difference wont shift the vhf-hi frequency much.

[ota_canuck]

300ohm,

The nec errors?

In stampeder's analogy,... his picture essentially shows that using tubing produces the same effect as if squeezing a 4221 'V' element closed to having only a 1" spacing instead of an open 'V' shape: http://www.digitalhome.ca/forum/pict...pictureid=5403. The open 'V' element has 14" of total element length whereas the tubing would only assimilate a 7" total length since the outer surfaces are so close and physically joined.

I expected that the frequency range would be out of wack. likely 9" or even 10" tubes may be needed,.. and possibly such lengthened tube lengths would then begin creeping the bandwidths down into the VHF upper frequencies.

Maybe taking the reflector out of the equation for now would help with driven element tube performance evaluation. Would a truer [error-less] nec picture of this tubular element design performance be better demontrated if the model was evaluated reflectorless? The reflector size and spacing could then be added later to optimize f/b ratio.

[holl_ands]

NEC2 is a THIN WIRE modeling program...to do it "right" each fat tube would
need to be modeled as a cylinder...at which point you'll probably want NEC4.

I think the very fat tubes should be providing a better SWR...thicker feedlines
are probably needed...try upgrading to AWG10....and if the feedline separation
is increased by moving the tubes further OUTWARDS, the Gain nosedive on the
lower channels can also be fixed....

[holl_ands]

W-G HD-4400 (aka PR-4400) 4-Bay Dipoles w 9 Refl. Rods:

4nec2 results have been uploaded here for comparison. It provides wideband,
VERY LOW SWR (under 2.3) performance by using very WIDE bars rather
than FAT tubes:
http://imageevent.com/holl_ands/mult...winegardhd4400

BTW: Mods to Ken Nist's w4400.ez.nec file were discussed earlier:
http://www.digitalhome.ca/forum/showthread.php?t=148569
NO Errors, but lots of Warnings re Sharp Angle/FAT wires....which I ignore...

[300ohm]

.thicker feedlines
are probably needed...try upgrading to AWG10....

Yes, even 1/4" aluminum rod for phase lines, which would make the structure basically self supporting.

Tomato steaks (green plastic coating).

Mmmmmmm, tomato steaks. The tomato stakes with the green plastic coating sold at Lowes, Home Depot, Walmart etc are plastic covered thin steel tube, not aluminum. Which is still fine for reflector usage.

Old, used aluminum lawn chairs are a good cheap source of 1" aluminum tube pieces. A lot of models even have rounded closed ends.

[BOUVAL]

When modeling, other than the dimensions, do you have to input the kind of metal used ?

I was thinking that next time my business slows down again I could build another 4 bay with Mclapp's classic M4 dimensions 9.5" x 9".

So I ask myself should I use the 1" or the .875" tubes ?

With the 1" tubes I can still use the PVC conduit, but with the .875" o.d. tubes which have .77" inside diameter don't know what to use.
.

[300ohm]

When modeling, other than the dimensions, do you have to input the kind of metal used ?

Yes, by using a LD card, type 5 and specifying the material conductivity.
If not specified, I believe it defaults to either copper or aluminum.

With the 1" tubes I can still use the PVC conduit, but with the .875" o.d. tubes which have .77" inside diameter don't know what to use.

3/4" CPVC may fit. I believe CPVC is more UV resistant than the white PVC, but much less UV resistant than the grey PVC. CPVC is also the priciest of the three.

[BOUVAL]

___ When modeling, what metal gives the most gain? Assuming the same specific design.
Personally I think that steel would be the best for the elements. The problem with steel is that it's heavier.

___ Why go with thicker phase lines? If we consider that a 4 bay like a CM4221HD has an impedance of around 225 omms, so going bigger would decrease the impedance more. And we know there's only a few milliamps going thru those phase lines.

___ I think I'll stick with the 1 inch tubes for my next 4 bay build and keep the .875" to build a Yagi for Balm's RF13
.

[old sparks]

Bouval;

Innovative construction idea!

Generally, steel is not the best choice for antennas, especially ferromagnetic steel. I have seen stainless steel used in some commercial yagi designs, but SS has greater losses than AL. On the other hand, the I^2R losses in each yagi element can really add up, but not so much in a collinear antenna like a 4-bay.

The phasing lines in a collinear antenna do provide for some impedance transformation, but this impedance transformation varies as the receive frequency changes.

I suspect that these fat elements have lower impedance than the Winegard HD4400 modelled by holl_ands. With NEC2-based software, I suspect they would be best modelled as 4 (or more)parallel wires, separated by the diameter of the tubing, joined at the ends.

[300ohm]

When modeling, what metal gives the most gain? Assuming the same specific design.

Silver has the best conductivity, but its a bit heavy and pricey, heh.
Wire conductivity
Below a wire conductivity table to be used for LD card type 5, wire loading
Material
Conductivity S/m
Perfect
9.90E+99
(lossless)
Silver
6.29E+07
Copper
5.80E+07
Pure Alumin.
3.77E+07
Al. 6063-T832
3.08E+07
Al. 6061-T6
2.49E+07
Brass
1.56E+07
Phospor bronze
9.09E+06
Stainless Steel 302
1.39E+06

Why go with thicker phase lines?

Structural. Then you could mount it to the mast with only points instead of 4.

so going bigger would decrease the impedance more.

Easy enough to go with wider spacing to compensate.
http://www.qsl.net/co8tw/openline.htm

[stampeder]

BOUVAL and all, be sure to check out the following thread. The info and ingenuity in there is amazing!

Best Metals for Antennas: Performance, Soldering, Welding, Bending, Working

We'll keep this present thread focused on modelling and testing your design.