Opinions on narrowband FM Radio antenna?

[Choclab]

I know this is really an OTA TV forum, but you guys know your stuff better and have more experience building than anyone...

My great old Winegard 6065 FM antenna got torn up in a freak storm a couple of weeks ago and I'd like to take a shot at building something to replace it. Part of my motivation is that the only stations I really care about happen to be from 103.3 to 107.7... Obviously a small part of the band, which helps tremendously. I don't think I'll need multiple driven elements, and it's also nice that the antenna can and will be smaller (or at least not as wide) when designed for the higher frequencies.

What would you guys recommend for a medium-sized yagi for my situation? The 107.7 is the more distant station... The 103.3 is 95 or so miles away but actually comes in very well with just an old Radioshack/Antennacraft FM-6, so I'm thinking I'd rather tilt things toward the higher end of the band. I've read Brian Beezley's site and seen his narrowband yagi designed for the low end of the band, and I could simply scale it for the higher end of the band, but it's larger than I want to build.

I was thinking of simply running a model for a 107.7 yagi but with a 103.3-sized reflector -- sort of the design of the Winegard YA1713. Or do you think a yagi designed for 107.7 or even right in between be better? I just know in looking at TV yagis, the gain drops off precipitously once past the peak frequency.

Thanks, would be interested in any thoughts you guys would have.

[holl_ands]

Antennacraft FM-6 is 70-in long with medium Gain (5-6 dBd = 7-8 dBi): [dBd + 2.15 dB = dBi]
http://www.antennacraft.net/pdfs/FM6.pdf
http://www.ham-radio.com/k6sti/curves.htm
So pretty much anything you chose from Beasley's chart would be an improvement.
Unfortunately, some of the best performers are either no longer in production (APS) or are
likely to be available only ($$$$) from overseas sources (Korner).

You didn't say what would be an "acceptable" boom length.....
K7MEM's On-Line (Narrowband, 50 or 200-ohm) Yagi Calculator results for 103 MHz.
Gain & dimensions are completely determined by the frequency....there are no in-betweens:
103 MHz, 5 Elements, 7.8 dBd = 10.0 dBi, 77.8-in long
103 MHz, 6 Elements, 8.9 dBd = 11.1 dBi, 105.5-in long
103 MHz, 7 Elements, 9.8 dBd = 12.0 dBi, 137.5-in long
103 MHz, 8 Elements, 10.6 dBd = 12.8 dBi, 172-in long
http://www.k7mem.150m.com/Electronic.../yagi_vhf.html

There are very few High Gain FM Antennas on the market (A-D, AntennaCraft & C-M are all low-gain).
Fortunately there are several choices that are only slightly longer than the obsolete A-C FM-6:
Winegard HD6055P, up to 9 dBi Gain, 82-in: http://www.winegard.com/kbase/upload/HD6055P.pdf
Wade C-55-FM, 9.5 dBi Gain, 79-in: http://www.wade-antenna.com/Wade/CSeries.pdf
Wade J-55-FM, 10 dBi Gain, 79-in: http://www.wade-antenna.com/Wade/jseriesyagi.pdf
I'm not sure what the length is for this one (148-in???)...their spec chart is very confusing:
Wade C-101-FM, 10.5 dBi Gain, ???-in: http://www.wade-antenna.com/Wade/CSeries.pdf

You might want to select one of the DIY projects on Beasley's website, perhaps
using the dimensions of one of the (too big???) high performance commercial antennas:
http://www.ham-radio.com/k6sti

Or rescale ALL of the dimensions of one of the Hi-VHF Yagi's I analyzed here:
http://imageevent.com/holl_ands/yagis [Dimensions found in the 4nec2 Files.]
Note Gain curves for most Yagi's slope upwards, reaching max on the highest freq.
Hi-VHF 10-Element Folded Dipole Yagi - Lorkoe's Antique: 11.5 dBi Gain, ~2*78-in long
Hi-VHF 8-El Ch11-13 Yagi (K7MEM On-Line Calculator): up to 13 dBi Gain, ~2*87-in long.
After 2:1 Rescale, these are probably too long for you....

To Rescale from say a Hi-VHF antenna with max Gain on Ch13 (216 MHz) to max Gain
on say 108 MHz), enlarge ALL dimensions by the ratio 216/108 = 2.0.
When I say ALL, I also mean the element diameters...although smaller, "standard" size
elements (e.g. 3/8-in) should work just fine in the FM Band....with a slightly higher SWR.
You can Rescale a 4nec2 File to make sure by multiplying all of the X,Y,Z parameters
by the above Rescale Factor (I define a Rescale Factor "F" via a SYmbol statement).

====================================================
If there is an FM Antenna thread on this forum, I couldn't find it. Here is
"EV's Best Top Rated FM and HD Radio Antenna Guide & Reviews":
http://www.dtvusaforum.com/dtv-hdtv-...e-reviews.html
Worldwide TV-FM DX Association (WTFDA) Forum also has a lot of useful info re FM Antennas, et. al.:
http://www.wtfda.info/forumdisplay.php?22-DX-Equipment

[Choclab]

Thanks, Holl_ands... I can't tell you how many hours I've spent looking over all the models on your site...

I thought of making Beezley's little 5-element with the funky angled driven element, but even that seems like a waste of boom space considering I really don't care about anything below 103.3.

I was going to use k7mem's yagi calculator to just design a yagi for 107.7 for as long as I thought I wanted to make it, which is probably around 10 feet max -- my 6065 is 127 inches IIRC and that's too big. Unless I'm missing something, that still should give plenty of gain at 103.3... We're only talking about barely over 4 mhz.

You guys let me know if I'm missing something on that.

[holl_ands]

There is about a 1 (excl) to 3 (good) channel bandwidth for the 8-element Yagi (a bit more if smaller).
The design frequency you punch into K7MEM's calculator would be several MHz less than the highest
frequency you want to receive....which is why 4nec2 modeling is so important...

nikiml, myself & others are currently working on a 7-Element Yagi for the Hi-VHF Band that you
might want to also consider. nikiml includes an extra parameter to try to find a good, SHORT solution.
So far, I have not tried to constrain the length. Currently we're investigating alternative optimization
methods using nikiml's python scripts:
http://www.digitalhome.ca/forum/show....php?p=1306095
Up to 12.5 dBi Gain, excellent SWR, Hi-VHF Length=63-in (so about 126-in Rescaled to FM Band).

I would expect to see someone try to optimize a higher Gain design for single channel use....soon....
I have an alternative idea for constraining the length I want to try....

==========================================================
SHAZAMM!!! My revised Hi-VHF 7-El Yagi 4nec2 model is beginning to find SHORT solutions.
Standby....it usually takes all night to complete the run...which will then tell me what I might
need to revise to get a better solution....ad nauseum.....so many antennas, so little time....

[nikiml]

Yes, it looks like 9+dbi are possible with yagi within 55x70in size

[Choclab]

What number would you recommend putting into the K7MEM calculator?

And just out of curiosity, why does that one need to be lower than my target frequency?

Cool VHF-Hi short-yagi project, BTW...

[nikiml]

One could try to minimize the total wire length needed for the build as well...

[stampeder]

Also you might want to look into building one of these, Choclab (see the discussion I had with 300ohm about scaling them for the FM Radio band):

Delhi 5y & 10y Channel Cut VHF Yagis - Saved From Oblivion For DIYers

[nikiml]

Choclab, do you have any F/R ratio requirements?

[300ohm]

Also you might want to look into building one of these, Choclab (see the discussion I had with 300ohm about scaling them for the FM Radio band):

Yeah, Choclab take a look at this rescaled 5Y6S for 108 mhz. 5 element, 9.4 dbi in a 58" X 58" package. You should have a good bit of usable material from your old Winegard 6065.

CM Dehli 5Y6S  rescaled to 108mhz
CM modeled by 300ohm
CM AGT 1.0 (0.02 db) at 108 mhz
CE
GW	1	11	0	0.93442934	1.12775954	0	26.9856745	1.12775954	0.1611085
GW	2	11	0	-0.9344294	1.12775954	0	-26.985674	1.12775954	0.1611085
GW	3	1	0	-0.9344294	1.12775954	0	0.93442934	1.12775954	0.14080883
GW	4	11	0	-26.985674	-1.1277595	0	0	-1.1277595	0.1611085
GW	24	11	0	0	-1.1277595	0	26.9856745	-1.1277595	0.1611085
GW	5	11	0	-26.985674	0	0	0	0	0.1611085
GW	6	11	0	0	0	0	26.9856745	0	0.1611085
GW	7	1	0	26.9856745	0	0	26.9856745	1.12775954	0.1611085
GW	8	1	0	26.9856745	0	0	26.9856745	-1.1277595	0.1611085
GW	9	1	0	-26.985674	0	0	-26.985674	1.12775954	0.1611085
GW	10	1	0	-26.985674	0	0	-26.985674	-1.1277595	0.1611085
GW	12	5	0	0	0	11.4387039	0	0	0.40277127
GW	13	5	11.4387039	0	0	22.8774077	0	0	0.40277127
GW	14	7	22.8774077	0	0	39.6326923	0	0	0.40277127
GW	15	11	-17.560827	0	0	-17.560827	29.0800852	0	0.1611085
GW	16	11	-17.560827	0	0	-17.560827	-29.080085	0	0.1611085
GW	17	11	11.4387039	0	0	11.4387039	25.3745895	0	0.1611085
GW	18	11	11.4387039	-3.576e-15	0	11.4387039	-25.374589	0	0.1611085
GW	19	11	22.8774077	0	0	22.8774077	24.569047	0	0.1611085
GW	20	11	22.8774077	0	0	22.8774077	-24.569047	0	0.1611085
GW	21	11	39.6326923	0	0	39.6326923	24.569047	0	0.1611085
GW	22	11	39.6326923	0	0	39.6326923	-24.569047	0	0.1611085
GW	23	7	-17.560827	0	0	0	0	0	0.40277127
GW	25	1	0	0	0	0	0	-1.1277595	0.40277127
GS	0	0	0.0254		' All in in.
GE	0
EK
LD	5	0	0	0	3.77e7	0
EX	0	3	1	0	1	0
GN	-1
FR	0	1	0	0	108	0

Charts in 1 mhz increments

[300ohm]

The above NEC file rescaled everything, including element and boom size. Heres the NEC file with 3/8th inch tubing and 1 inch boom. The charts are identical, +/- .1 dbi net, so I wont repost them.

CM Dehli 5Y6S  rescaled to 108mhz
CM modeled by 300ohm
CM AGT 1.0 (0 db) at 108 mhz
CE
GW	1	11	0	0.93442934	1.12775954	0	26.9856745	1.12775954	0.1875
GW	2	11	0	-0.9344294	1.12775954	0	-26.985674	1.12775954	0.1875
GW	3	1	0	-0.9344294	1.12775954	0	0.93442934	1.12775954	0.16
GW	4	11	0	-26.985674	-1.1277595	0	0	-1.1277595	0.1875
GW	24	11	0	0	-1.1277595	0	26.9856745	-1.1277595	0.1875
GW	5	11	0	-26.985674	0	0	0	0	0.1875
GW	6	11	0	0	0	0	26.9856745	0	0.1875
GW	7	1	0	26.9856745	0	0	26.9856745	1.12775954	0.1875
GW	8	1	0	26.9856745	0	0	26.9856745	-1.1277595	0.1875
GW	9	1	0	-26.985674	0	0	-26.985674	1.12775954	0.1875
GW	10	1	0	-26.985674	0	0	-26.985674	-1.1277595	0.1875
GW	12	5	0	0	0	11.4387039	0	0	0.5
GW	13	5	11.4387039	0	0	22.8774077	0	0	0.5
GW	14	7	22.8774077	0	0	39.6326923	0	0	0.5
GW	15	11	-17.560827	0	0	-17.560827	29.0800852	0	0.1875
GW	16	11	-17.560827	0	0	-17.560827	-29.080085	0	0.1875
GW	17	11	11.4387039	0	0	11.4387039	25.3745895	0	0.1875
GW	18	11	11.4387039	-3.576e-15	0	11.4387039	-25.374589	0	0.1875
GW	19	9	22.8774077	0	0	22.8774077	24.569047	0	0.1875
GW	20	9	22.8774077	0	0	22.8774077	-24.569047	0	0.1875
GW	21	9	39.6326923	0	0	39.6326923	24.569047	0	0.1875
GW	22	9	39.6326923	0	0	39.6326923	-24.569047	0	0.1875
GW	23	7	-17.560827	0	0	0	0	0	0.5
GW	25	1	0	0	0	0	0	-1.1277595	0.5
GS	0	0	0.0254		' All in in.
GE	0
EK
LD	5	0	0	0	3.77e7	0
EX	0	3	1	0	1	0
GN	-1
FR	0	1	0	0	108	0

[Choclab]

Nik, no f/r requirements... I live in a small city without many stations, and none around these, so gain is most important.

And thanks, 300ohm, that looks really good for that short a boom length. I'll try to load that up on the NEC.

BTW, that thread reminds me, I never posted back on the measurements of my 10y9s, but I guess you guys got it all scaled from a different channel anyway. The 10y9s was torn up, too, though most of the damage was the boom breaking in half at the back. I can at least fix that. The 6065's elements got totally mangled to the point that I don't think they can really be straightened... It being the largest antenna and the one at the bottom, it took the brunt of the fall. The CM old UHF 4248 at the top of the mast was perfectly fine... And it was the most easily replaced of the three. Isn't that the way it usually works.

Thanks again. Now I need to read up on the construction/materials thread. For some reason here in the States, at least where I live, 3/8" aluminum tubing is hard to find. I was actually thinking of trying 1/2" metal conduit, as it's only $1.90 for 10 feet. Or even some type of thin, flat shelving material, much like Winegard uses on their UHF yagis.

And edit, thanks double for the rescale, 300! That post wasn't up when I started typing. Very nice of you to go to the trouble.

[300ohm]

The 10y9s was torn up, too, though most of the damage was the boom breaking in half at the back.

Yeah, 1" boom material is easier to get cheap than 3/8" tubing.
1" aluminum tube is used in a lot of stuff, like lawn chairs, umbrella type clothes lines, mop handles to name a few items.

The 6065's elements got totally mangled to the point that I don't think they can really be straightened..

What did it do ? Roll around ?

I wouldnt toss them out though, theres probably plenty of straight material for uhf use.

[nikiml]

One hour run of my scripts came up with a number of short solutions.
I have selected 3 with length from 55 to 96 in, and with <=56in.
All results are for impedance of 200 Ohm.

55in length 7-element model

  Freq  RawGain  NetGain     SWR     F/R     Real     Imag    AGT(corr)
=========================================================================
 103.0    9.426    8.919   1.993   9.570   122.35    77.94  1.00( 0.004)
 104.0    9.576    9.219   1.781  10.750   163.42    99.31  1.00( 0.004)
 105.0    9.616    9.382   1.595  11.430   210.75    96.07  1.00( 0.004)
 106.0    9.606    9.490   1.387  11.850   241.63    59.03  1.00( 0.004)
 107.0    9.596    9.578   1.136  12.260   225.30     9.61  1.00( 0.004)
 108.0    9.596    9.563   1.190  12.880   169.07    -8.38  1.00( 0.004)

68in 6 element ( I removed the reflector cause was too short )model:

  Freq  RawGain  NetGain     SWR     F/R     Real     Imag    AGT(corr)
=========================================================================
 103.0    9.385    9.142   1.608  11.650   191.45    93.45  1.00( 0.005)
 104.0    9.585    9.229   1.780  10.140   210.40   119.49  1.00( 0.005)
 105.0    9.735    9.308   1.882   8.870   239.60   134.99  1.00( 0.005)
 106.0    9.865    9.472   1.834   8.020   270.68   124.61  1.00( 0.005)
 107.0   10.025    9.797   1.584   7.780   267.37    83.43  1.00( 0.005)
 108.0   10.275   10.150   1.404   8.600   198.19    67.92  1.00( 0.005)

96in 7 element model:

  Freq  RawGain  NetGain     SWR     F/R     Real     Imag    AGT(corr)
=========================================================================
 103.0   10.685   10.246   1.899  18.040   105.36    -3.63  1.00( 0.005)
 104.0   10.915   10.606   1.711  17.740   119.83    25.42  1.00( 0.005)
 105.0   11.075   10.853   1.575  15.730   142.70    52.05  1.00( 0.005)
 106.0   11.165   11.019   1.446  13.900   178.61    66.77  1.00( 0.005)
 107.0   11.195   11.138   1.258  12.730   219.35    44.19  1.00( 0.005)
 108.0   11.215   11.201   1.120  12.420   201.74   -22.77  1.00( 0.005)

I can post any of them, but I think the best approach would be if you figure out few things first:
1) the gain needed (lets say at 107)
2) the max acceptable length / the preferred length
3) boom and element materials

and based on those a proper nec file should be optimized with a proper target function.

[Choclab]

What did it do ? Roll around ?

I don't know, exactly. But the elements aren't just bent, but twisted. I've tried to straighten them out -- and a few of them did straighten okay -- but most of them are so weak now that I don't think they'll be straight enough to be effective.

It's very strange, because we've been in literally the worst drought ever recorded here, with barely the sight of a rain cloud the last many months... But apparently the edge of a little storm just brushed us and caused this. I live in an area of violent thunderstorms, and I know for a fact that my setup has survived many 65-70 mph (at least) winds over the last eight years, yet this is what takes it down. Guess that's Mother Nature for you.

Anyway... You're right that there are at least parts of it I can salvage, maybe for a future UHF yagi.

And nikiml, the 96-inch one would be perfect, as Home Depot sells a piece of 1" square aluminum tubing at that exact length. I was thinking of using 1/2" round metal conduit, fastened by conduit straps. That's about the most cost-effective solution I can think of. I'd planned to make a folded dipole driven element from some 9 gauge aluminum ground wire I have.

Thanks so much, guys... I started this thread just for some general theories and guidance, not to put anyone to work! So please, don't spend much (if any) time on this. Those gains are already way better than I was expecting, even at the shorter lengths.