Bow Tie TV Antenna Designs (mclapp's M4 featured)

[balm]

its because his TVFool is for the Montrealish area...

[stampeder]

Oh ya, he has a friend living near Concordia. See the City of Montreal thread.

[keithr386]

Sorry if I caused any confusion here. I posted in this thread because my question was more about the abilities of the M4. It is all well and good to have line of site at 76 miles, but you also need a suitable antenna to grab the signal. I wanted to know if 76 miles was too far for the M4 (especially for a VHF-HI channel, in this case, ABC), so I thought this thread would be more appropriate than the Montreal thread.

[balm]

keith,

I wanted to know if 76 miles was too far for the M4 (especially for a VHF-HI channel, in this case, ABC),

No (assuming no obstacles of course)

[mclapp]

I was getting a station on ch11 @ 80mi this weekend during my testing, only the 9 1/2 x 9 and 9 x 8 1/2" would lock it. The 10 x 9 1/2" wouldn't although it did have better signal strength on CH's 7 and 8. All used the same 36" wide reflector spaced @ 4 1/2".

I will be posting more when I get the data all organized. I was using an amp to get the CH 11 station @ 80 miles it showed a signal of 32 on my apex DT 250a signal meter, that is considered on the border of weak to good by the scale on the converter box. The CH11 yagi was getting a signal of 37 without the amp, judging how much difference the amp makes the yagi would have probably got a signal in the 50's with the amp.

I would say that is pushing the limit of that style antenna and I would not consider it typical but possible depending on transmitter power and terrain.

[keithr386]

Thanks for the great feedback, McLapp, and look forward to seeing more data. It looks like it is at least worth testing, and possibly adding some kind of pre-amp into the mix to get that channel 13 (VHF-HI). Do you think making the M8 variety (either stacked vertically or ganged horizontally) would increase the likelihood of a consistent lock?

[balm]

keith,

im in the west island, with lower NM, and over 80 miles distance, and I picked up ABC with my M4 since I started last fall (at 39 ft), some weather can cause slight dropping out, i think it happened 2 times!


The M4 is excellent (i think mine was 91/2 x 9, with 36" reflector), the key for me(for ABC) was putting the reflector at 15" back - I havent even added an amp yet...

the local reception threads (Montreal are) are not useful feedback for the M4 because Montrealers dont realize how good an antenna it is and noone uses it here, most go for CM, or GHs,

Mclapp REALLY knows his antennas too!

[keithr386]

Originally Posted by balm

The M4 is excellent (i think mine was 91/2 x 9, with 36" reflector), the key for me(for ABC) was putting the reflector at 15" back - I havent even added an amp yet...

Most interesting, balm. How did you come to try 15 inches depth for the reflector? Did you just play around with it until something worked, or did you do some research (and would you care to share)?

the local reception threads (Montreal area) are not useful feedback for the M4 because Montrealers dont realize how good an antenna it is, most go for CM, or GHs

That is why I posted here.

[balm]

from mclapp:

The ideal reflector spacing for uhf is about 4" the larger 15" reflector spacing will inhance some VHF-HI channels but at the expence of some band width on UHF.

mclapp can better answer your questions, but I think it lowers SWR on channel 13, thus making greater net gain (around 7 dbi),

and i wouldnt worry about the UHF ones, as they are quite strong enough to cover any decline in gain there

[mclapp]

The 15" reflector spacing helps the over all VHF-hi SWR but it will most likely not be better on the few VHF-hi channels that the 4" spacing is already works best on.

So here is the run down a 10 x 9 1/2" will work best on channels 7 - 9 a 9 1/2 x 9" will work best on 9 - 11 and a 9 x 8 1/2" will work best on ch's 11 -13. This is all using a 4 -5" reflector spacing and a 34" minimum width reflector.

The 15" spacing will generally not improve these channels much over the 4-5" spacing but will improve all the others.

A M8 vertical stack with 4-5" spacing will be better and the same size rules appear to apply according to computer modeling. I've only tested the 10 x 9 1/2" version and it is strong on 7 - 8 but will also pick up a ch11 station @ 80 mi. about as well as the M4 9 x 8 1/2" will.

So to sum this up if you need overall VHF-hi coverage then the wider spacing may be best but if you only need to concentrate on a certain range of channels then the proper sized elements with 4-5" spacings will do the job just as well.

I will be building a 9 1/2 x 9" vertical stack to test so I will see how it performs on the distant weak ch's 11 and 13.

[holl_ands]

Hi-VHF 2-Bay and 4-Bay Bowties (NO Reflectors) were analyzed to find quasi-optimum (33"x32")
dimensions (overall 49" H x 33" W and HUGE 113" H x 33" W respectively):
http://imageevent.com/holl_ands/multibay
I also analyzed response in the UHF Band...yes there is good Gain...but it's all over the place...

These NO Reflector versions would be suitable for hanging on the wall behind a picture or curtain....

Hi-VHF 2-Bay NO Refl: 7.5-10.0 dBi Raw Gain, SWR 2.2-3.5 with AWG10 (Fatter would be better).
Hi-VHF 4-Bay NO Refl: 10.8-12.3 dBi Raw Gain, SWR 1.1-2.8 with AWG10.

Compare to:
Hi-VHF Folded Dipole: 2.1-2.2 dBi Raw Gain, SWR 1.1-2.5 with AWG12.
Hi-VHF Circular Loop: 3.5-4.5 dBi Raw Gain, SWR 1.7-2.6 with AWG12.

[300ohm]

That 33"x32" VHF-Hi 2bay is very close in size to the common old all VHF 2 bay bowtie. I dont think it was over 40 X 32. Here a piece from an old one I had :



The feedpoint (the closest the metal comes together) is 1 3/8". The distance between the upward posts is 2.2" on center. The angle is 30 degrees off Y on each side, making a 120 degree forward sweep angle. It had a shorter straight middle element in the middle between the Vees, probably about 12". to 18". The spread angle of the Vees is 38 degrees.

============================================================ =========================

By simply closing the ends of the 33"x32" VHF-Hi 2bay above, (no more space is required) you get a bit better FM gain at the expense of a bit less channel 12 and 13 gain.

[holl_ands]

Hi-VHF Four-Whisker, Six-Whisker, Enclosed and Indented Bowties (NO Reflectors)
analyzed using 4nec2. Performance on Ch2-6 + FMBand was included. They continue to
operate as Bi-directional Dipoles with low Gain and much higher SWR on the lower channels:
http://imageevent.com/holl_ands/dipoles/hivhfbowtie

Six-Whisker Bowtie had better Raw Gain than Four-Whisker and much better SWR than either
Four-Whisker, Enclosed or Indented Bowties. [Still need to try an Eight-Whisker.]

Yup, these simple Bowties have a bit of Gain on Ch2-FM, with an SWR of about 4 in FM Band,
increasing to about 11-14 on CH2....but the Enclosed Bowtie wasn't all that different.
And just like the 2-Bays and 4-Bays, no one would like the Azimuthal Pattern in the UHF Band.

300ohm: Coincidently I just finished the Bowtie comparison and will do some comparison
charts "soon"....meanwhile I continue to plug away in the background on the 8-Bays....

[holl_ands]

Multi-Bay Bowtie 4nec2 Analysis Additions and Revisions:
http://imageevent.com/holl_ands/multibay

1. Hi-VHF 2-Bay & 4-Bay Bowties (NO Reflector): Added Ch2-FM Band performance.
SWR and Raw Gain over the FM Band is very usable, but SWR is much higher on Ch6 and
excessive on Ch2-5....however, YMMV.....

2. Hi-VHF 2-Bay with 56"x72" Flat Reflector (2"Hx4"W) Hi-VHF & Ch2-FM Band - All New.
SWR for Ch2-FM was excessive, except for perhaps the top end of the FM Band,
but if the signal strength is strong enough and the VSWR nulls occur somewhere other
than the end of the coax (and the phase of the moon....)....as usual, YMMV....

3. UHF M4 (9.5x9.0) Flat vs Swept Bowties (under UHF 4-Bay Bowties w Refl.):
Added Ch2-FM Band performance and reran UHF & Hi-VHF results (due to a file
editing error, one whisker was missing). Impact on results was very minor, notable
change was 0.5 dB better above Ch51. Analyzed ALL AWG10 M4, in addition to
AWG8 (elements) & AWG12 (feedline) in mclapp's drawings.

4. UHF mclapp's M4 (9.5x9.0) 4-Bay - NO Refl (under UHF 4-Bay Bowties - if NO Refl.):
Added analysis of Forward Swept Bowties. No improvement in Gain, except above Ch51.

5. UHF Old CM-4228 with RF Combiner Mod (under UHF 8-Bay Bowties w Refl):
Added analysis of using an RF Combiner in a standard Horizontal Stack
configuration, rather than the crossover feedline between the left & right 4-Bays.
Significant Raw Gain improvement for low UHF channels and especially above Ch51....
but Net Gain only improved above Ch51 due to the RF Combiner Mod degrading
SWR on the low UHF channels.

6. Updated Multi-Bay Comparison Charts:
http://imageevent.com/holl_ands/multibay/compare

[300ohm]

56" X 72" is still a very reasonable size for the amount of gain it gets on vhf-hi, about 3 dBi avg over the vhf-hi loop with reflector. And puts it up there on the charts better than the YA-1713 http://www.hdtvprimer.com/ANTENNAS/comparing.html

A strong cheap frame for the mesh could be built from 1/2" galv EMT, and then ubolted in the center to a mast.