DIY UHF log-periodic

Xauto · Dec 5, 2011

Has anyone make a UHF (14-51) log antenna with 14guage wire like this?
CM Experimental Antenna Design
CM Log
CE
GW 1 1 1.46 0 -0.25 1.46 0 0.25 0.045
GW 2 4 0 -2.8 -0.25 0 0 -0.25 0.032
GW 3 4 0 0 0.25 0 2.8 0.25 0.032
GW 4 3 -1.83 0 0.25 0 0 0.25 0.032
GW 5 3 -1.83 0 -0.25 0 0 -0.25 0.032
GW 6 4 -1.83 0 0.25 -1.83 -3.5 0.25 0.032
GW 7 4 -1.83 0 -0.25 -1.83 3.5 -0.25 0.032
GW 8 3 -4.13 0 0.25 -1.83 0 0.25 0.032
GW 9 3 -4.13 0 -0.25 -1.83 0 -0.25 0.032
GW 10 5 -4.13 0 0.25 -4.13 4.4 0.25 0.032
GW 11 5 -4.13 0 -0.25 -4.13 -4.4 -0.25 0.032
GW 12 4 -7 0 -0.25 -4.13 0 -0.25 0.032
GW 13 4 -7 0 0.25 -4.13 0 0.25 0.032
GW 14 6 -7 0 0.25 -7 -5.5 0.25 0.032
GW 15 6 -7 0 -0.25 -7 5.5 -0.25 0.032
GW 16 5 -10.6 0 -0.25 -7 0 -0.25 0.032
GW 17 5 -10.6 0 0.25 -7 0 0.25 0.032
GW 18 9 -10.6 0 -0.25 -10.6 -6.9 -0.25 0.032
GW 19 9 -10.6 0 0.25 -10.6 6.9 0.25 0.032
GW 20 6 -15.08 0 -0.25 -10.6 0 -0.25 0.032
GW 21 6 -15.08 0 0.25 -10.6 0 0.25 0.032
GW 22 11 -15.08 0 0.25 -15.08 -8.8 0.25 0.032
GW 23 11 -15.08 0 -0.25 -15.08 8.8 -0.25 0.032
GW 24 2 1.46 0 0.25 0 0 0.25 0.032
GW 25 2 1.46 0 -0.25 0 0 -0.25 0.032
GW 26 3 1.46 0 -0.25 1.46 2.2 -0.25 0.032
GW 27 3 1.46 0 0.25 1.46 -2.2 0.25 0.032
GS 0 0 0.0254 ' All in in.
GE 0
EK
EX 0 1 1 0 1 0
GN -1
FR 0 1 0 0 584 0
XQ
EN

300ohm · Dec 5, 2011

A long while ago, I posted a NEC file of this rusty commercial uhf lpda (make still unknown, but it was made in the late sixties) :

The plexi pieces werent stock, I added those.

NEC file:

Code:

CE
GW	1	1	0	0	1.25	0.3	0	1.25	0.1022
GW	2	5	0	0	1.25	0	-1.25	1.25	0.1022
GW	3	9	0.3	0	1.25	3.3	0	1.25	0.1022
GW	4	7	3.3	0	1.25	6.05	0	1.25	0.1022
GW	5	7	6.05	0	1.25	8.55	0	1.25	0.1022
GW	6	7	8.55	0	1.25	10.8	0	1.25	0.1022
GW	7	5	10.8	0	1.25	12.8	0	1.25	0.1022
GW	8	5	12.8	0	1.25	14.55	0	1.25	0.1022
GW	9	5	14.55	0	1.25	15.8	0	1.25	0.1022
GW	10	3	15.8	0	1.25	16.8	0	1.25	0.1022
GW	11	3	16.8	0	1.25	17.55	0	1.25	0.1022
GW	12	2	17.55	0	1.25	18.05	0	1.25	0.1022
GW	13	1	18.05	0	1.25	18.3	0	1.25	0.1022
GW	14	5	18.3	0	1.25	18.3	1.25	1.25	0.1022
GW	15	5	18.3	1.25	1.25	18.3	1.25	0	0.1022
GW	16	5	0	-1.25	1.25	0	-1.25	0	0.1022
GW	17	3	0	-1.25	0	-0.75	-1.25	0	0.1022
GW	18	3	18.3	1.25	0	19.05	1.25	0	0.1022
GW	19	11	0.3	0	1.25	0.3	-4.15	1.25	0.06424494
GW	20	7	0.3	-4.15	1.25	-1.95	-4.15	1.25	0.06424494
GW	21	11	3.3	0	1.25	3.3	4.15	1.25	0.06424494
GW	22	11	6.05	0	1.25	6.05	-4.15	1.25	0.06424494
GW	23	11	8.55	0	1.25	8.55	4.15	1.25	0.06424494
GW	24	11	10.8	0	1.25	10.8	-4.15	1.25	0.06424494
GW	25	5	3.3	4.15	1.25	1.7	4.15	1.25	0.06424494
GW	26	3	6.05	-4.15	1.25	4.85	-4.15	1.25	0.06424494
GW	27	3	8.55	4.15	1.25	7.7	4.15	1.25	0.06424494
GW	28	1	10.8	-4.15	1.25	10.45	-4.15	1.25	0.06424494
GW	29	11	12.8	0	1.25	12.8	4	1.25	0.06424494
GW	30	9	14.55	0	1.25	14.55	-3.6	1.25	0.06424494
GW	31	9	15.8	0	1.25	15.8	3.4	1.25	0.06424494
GW	32	9	16.8	0	1.25	16.8	-3.25	1.25	0.06424494
GW	33	9	17.55	0	1.25	17.55	3.2	1.25	0.06424494
GW	34	9	18.05	0	1.25	18.05	-3	1.25	0.06424494
GW	35	1	0	0	-1.25	0.3	0	-1.25	0.1022
GW	36	5	0	0	-1.25	0	1.25	-1.25	0.1022
GW	37	9	0.3	0	-1.25	3.3	0	-1.25	0.1022
GW	38	7	3.3	0	-1.25	6.05	0	-1.25	0.1022
GW	39	7	6.05	0	-1.25	8.55	0	-1.25	0.1022
GW	40	7	8.55	0	-1.25	10.8	0	-1.25	0.1022
GW	41	5	10.8	0	-1.25	12.8	0	-1.25	0.1022
GW	42	5	12.8	0	-1.25	14.55	0	-1.25	0.1022
GW	43	5	14.55	0	-1.25	15.8	0	-1.25	0.1022
GW	44	3	15.8	0	-1.25	16.8	0	-1.25	0.1022
GW	45	3	16.8	0	-1.25	17.55	0	-1.25	0.1022
GW	46	2	17.55	0	-1.25	18.05	0	-1.25	0.1022
GW	47	1	18.05	0	-1.25	18.3	0	-1.25	0.1022
GW	48	5	18.3	0	-1.25	18.3	-1.25	-1.25	0.1022
GW	49	5	18.3	-1.25	-1.25	18.3	-1.25	0	0.1022
GW	50	5	0	1.25	-1.25	0	1.25	0	0.1022
GW	51	3	0	1.25	0	-0.75	1.25	0	0.1022
GW	52	3	18.3	-1.25	0	19.05	-1.25	0	0.1022
GW	53	11	0.3	0	-1.25	0.3	4.15	-1.25	0.06424494
GW	54	7	0.3	4.15	-1.25	-1.95	4.15	-1.25	0.06424494
GW	55	11	3.3	0	-1.25	3.3	-4.15	-1.25	0.06424494
GW	56	5	6.05	0	-1.25	6.05	4.15	-1.25	0.06424494
GW	57	11	8.55	0	-1.25	8.55	-4.15	-1.25	0.06424494
GW	58	11	10.8	0	-1.25	10.8	4.15	-1.25	0.06424494
GW	59	5	3.3	-4.15	-1.25	1.7	-4.15	-1.25	0.06424494
GW	60	3	6.05	4.15	-1.25	4.85	4.15	-1.25	0.06424494
GW	61	3	8.55	-4.15	-1.25	7.7	-4.15	-1.25	0.06424494
GW	62	1	10.8	4.15	-1.25	10.45	4.15	-1.25	0.06424494
GW	63	11	12.8	0	-1.25	12.8	-4	-1.25	0.06424494
GW	64	9	14.55	0	-1.25	14.55	3.6	-1.25	0.06424494
GW	65	9	15.8	0	-1.25	15.8	-3.4	-1.25	0.06424494
GW	66	9	16.8	0	-1.25	16.8	3.25	-1.25	0.06424494
GW	67	9	17.55	0	-1.25	17.55	-3.2	-1.25	0.06424494
GW	68	9	18.05	0	-1.25	18.05	3	-1.25	0.06424494
GW	69	7	19.05	1.25	0	19.05	-1.25	0	0.077
GS	0	0	0.0254		' All in in.
GE	0
EK
EX	0	69	4	0	1	0
LD	5	0	0	0	1390000
GN	-1
FR	0	38	0	0	473	6

A long while ago, I did build a copper replica of it that worked better than the iron version even with cleaned up terminals.

UHF (14-51)

Yours actually peaks at 770 mhz, channel 64.

old sparks · Dec 5, 2011

Yes.

http://www.qsl.net/v/va3rr//hdtv/HDTV.htm

Xauto · Dec 5, 2011

Thank you old sparks and 300ohm for your examples.

holl_ands · Dec 6, 2011

oldsparks: Your 8-Element Pair UHF LPDA is a very elegant design approach, running the coax
feedline THRU one of the booms...I like it even more than this 7-El Pair, running coax OUTSIDE the boom:
http://www.vk2zay.net/article/43
And so much better than the fol. 9-El Pair tinker-toy approach:
http://www.youtube.com/watch?v=PtKnpjWmj_8

VK4ADC's 13-El Pair UHF LPDA is a bit more rugged for outdoor use...and optional Hi-VHF Elements:
http://www.vk4adc.com/web/index.php/vhfuhf-projects/23-tv-antennas/54-uhf-tv-lpy.html

FYI: ZS6BTE wrote a LPDA article "Wideband Antennas for the TV DXer" a while ago,
but it is no longer on QST.NET. I posted 4nec2 analysis of his 45-El Pair UHF LPDA as well
as a 14-El Pair Hi-VHF LPDA that I compared to my 14-El Pair Hi-VHF Zig-Zag LPA designs:
http://imageevent.com/holl_ands/zigzaglpa/lpda

holl_ands · Dec 6, 2011

XAuto: Very strange Raw Gain curve....consistent 6.15-6.35 dBi across New UHF Band
and then it jumps up to 7.6 dBi peak on 770 MHz. It shouldn't be doing that and probably
is "taking away" from Gain on the low frequencies to form that peak....

BTW: Gain & SWR doesn't even begin to fall-off until it reaches 300 MHz on the low end
and 950 MHz on the top end....only anomaly is that peak on 770 MHz, for which I have
NO CLUE as to WHY.....

300ohm · Dec 6, 2011

....only anomaly is that peak on 770 MHz, for which I have
NO CLUE as to WHY.....

My guess is that are half wave AND full wave reflectors for that frequency.

Xauto · Dec 6, 2011

Holl_ands: Thank you for the links. Now I need to build.

300ohm · Dec 7, 2011

Xauto, you can also use the program LPCAD to quickly design 75 ohm LPDA's. It has an option to save the design in 4nec2 .nec format.

(You can also save in the K6STI AO format)

http://wb0dgf.com/LPCAD.htm

Xauto · Dec 7, 2011

It looks like this antenna is going to work for me. My best antenna has been SBT (14.5"Dia. it has a 92 score). This little(16.5" by 17.6") log scores 91.

kc2cbd · Dec 7, 2011

Could you added a Corner reflector to one of these?
Seems it would raise the gain.

holl_ands · Dec 8, 2011

Hurray, LPCAD34 runs under Vista64....I no longer have to fire up the old laptop...

Since LPCAD34 takes the highest frequency of operation and adds 30%, there is no need
to inflate the highest frequency parameter, as in other calculators.
I entered F(low)=470 MHz, F(high)=698, Tau=0.9, Sigma=0.17 (optimum),
Rear Element Diameter=0.0641 (AWG14), which generated the desired 7-Element LPDA.
[Slightly higher Tau may generate LPDAs with more elements.]

[LPCAD34 also provides a design whereby the user enters the number of elements and
boom length (presuming you are clairvoyant enough to know which is a GOOD design).]

When I try to change characteristic impedance from 86-ohms to 75-ohm, LPCAD34
advises that there could be a VSWR peak if I didn't raise the Tau or do other adjustments.
[When I see these VSWR peaks, they coincide with Raw Gain anomalies.....]

When I tried to save as a *.nec type file, it further advised that a Shorting Stub is
needed to adjust VSWR....but didn't calculate the appropriate Stub Length other than
to advise that it should be less than 1/4-wavelength on lowest freq (6.28-in).
I tried various Stub Lengths (Lstub in 4nec2 file), finding a good result when Lstub=5.0.

LPCAD43 also will save design parameters to a *.LPD text file...and has a PRINT
(to Default) capability....but I didn't see any quick and easy way to save the screens
other than brute-force PRINT-SCREEN to *.bmp.....CROP/SAVE as compressed *.jpg.
Fortunately, most of the important design parameters are found in the *.nec file.

Fol. 4nec2 file provides Raw Gain between 7.7-9.0 dBi with SWR under 2.1.
Note that LPCAD34 makes the element radius smaller on shorter elements.....
If ALL of the radii are changed to 0.032 (AWG14), Raw Gain is between 7.6-9.0 dBi
and SWR is under 2.2. BOOM LENGTH=25.4-in, including 5-in Shorting Stub:

Code:

CM NEW UHF BAND, 7-El LPDA, Tau=0.9, 75-ohm, 5-in ShortStub, holl_ands run on 7Dec2011
CE Created by LPCAD 3.4, Variable Elem. Radius.  No Errors or Warnings, AGT=1.0.
CM F1 = 470 MHz, FH = 698 MHz, Num elements = 7, L/D =  200.2021.
CM TAU = 0.9, SIGMA = 0.17, Input Z = 75 ohms, Feeder Z = 86 ohms.
'
SY Lstub=5.0	' Shorting Stub Length.
GW 1 23    0.000     -6.406 0.000     0.000    6.406 0.000    0.032
GW 2 21    4.356     -5.766 0.000     4.356    5.766 0.000    0.029
GW 3 19    8.277     -5.189 0.000     8.277    5.189 0.000    0.026
GW 4 17   11.806     -4.670 0.000    11.806    4.670 0.000    0.023
GW 5 15   14.982     -4.203 0.000    14.982    4.203 0.000    0.021
GW 6 13   17.840     -3.783 0.000    17.840    3.783 0.000    0.019
GW 7 11   20.412     -3.405 0.000    20.412    3.405 0.000    0.017
GW 100 3  -Lstub     -0.320 0.000    -Lstub    0.320 0.000    0.032
GS 0 0 0.0254		' ALL IN INCHES.
GE 0
EK 0 
EX 0 7 6 0 1. 0.
TL 1 12 2 11  -86 0. 0. 0. 0. 0.
TL 2 11 3 10  -86 0. 0. 0. 0. 0.
TL 3 10 4 9  -86 0. 0. 0. 0. 0.
TL 4 9 5 8  -86 0. 0. 0. 0. 0.
TL 5 8 6 7  -86 0. 0. 0. 0. 0.
TL 6 7 7 6  -86 0. 0. 0. 0. 0.
TL 100 2 1  12 86 0. 1000. 0. 0. 0.
GN -1				' Free Space
' FR Freq Sweep choices in order of increasing calculation time (fm holl_ands):
' FR 0 0 0 0 470 0		' Fixed Freq
FR 0 29 0 0 470 12		' Freq Sweep 470-806 every 12 MHz - OLD UHF BAND
' FR 0 34 0 0 410 12		' Freq Sweep 410-806 every 12 MHz - Even Wider Sweep
' FR 0 39 0 0 470 6		' Freq Sweep 470-698 every 6 MHz - PREFERRED FOR UHF
' FR 0 77 0 0 470 3		' Freq Sweep 470-698 every 3 MHz
' FR 0 153 0 0 470 1.5		' Freq Sweep 470-698 every 1.5 MHz
' FR 0 71 0 0 300 10		' Freq Sweep 300-1000 every 10 MHz - WIDEBAND SWEEP
' FR Hi-VHF choices:
' FR 0 15 0 0 174 3		' Freq Sweep 174-216 every 3 MHz
' FR 0 29 0 0 174 1.5		' Freq Sweep 174-216 every 1.5 MHz - PREFERRED
' FR 0 43 0 0 174 1		' Freq Sweep 174-216 every 1 MHz - Hi-Rez
' FR 0 26 0 0 150 6		' Freq Sweep 150-300 every 6 MHz - WIDEBAND SWEEP
' FR Lo-VHF choices:
' FR 0 35 0 0 54 1		' Frequency Sweep every 1 MHz for Ch2-6
' FR 0 36 0 0 75 1		' Frequency Sweep every 1 MHz for Ch5 + Ch6 + FM
' FR 0 28 0 0 54 6		' Wide Freq Sweep every 6 MHz for Ch2-13
' FR 0 64 0 0 54 12		' Super Wide Freq Sweep 54-810 every 12 MHz
' RP choices in order of increasing calculation time:
' RP 0 1 1 1510 90 90 1 1 0 0	' 1D Gain toward 0-deg Azimuth - SIDE GAIN
' RP 0 1 1 1510 90 0 1 1 0 0	' 1D Gain toward 90-deg Azimuth - FORWARD GAIN
' RP 0 1 1 1510 90 180 1 1 0 0	' 1D Gain toward 270-deg Azimuth - REVERSE GAIN
' RP 0 1 37 1510 90 0 1 5 0 0 	' 2D (Left only) Azimuthal Gain Slice
RP 0 1 73 1510 90 0 1 5 0 0 	' 2D Azimuthal Gain Slice - PREFERRED
' RP 0 73 1 1510 90 0 5 1 0 0 	' 2D Elevation Gain Slice
' RP 0 73 73 1510 90 0 5 5 0 0 	' 3D Lower Hemisphere reveals antenna (Fixed Freq)
' RP 0 285 73 1510 90 0 5 5 0 0	' 3D Full Coverage obscures antenna (Fixed Freq)
EN

300ohm · Dec 8, 2011

Could you added a Corner reflector to one of these?
Seems it would raise the gain.

Sure, and directors too. Winegard and Antenna Craft have uhf lpda models with corner reflector and directors.

300ohm · Dec 8, 2011

LPCAD43 also will save design parameters

Just like 4nec2's build program, it also saves the file to the same directory the program started in.

majortom · Dec 8, 2011

When I try to change characteristic impedance from 86-ohms to 75-ohm, LPCAD34
advises that there could be a VSWR peak if I didn't raise the Tau or do other adjustments.
[When I see these VSWR peaks, they coincide with Raw Gain anomalies.....]

I was hacking around with it too for a while last nite in linux (under wine), and saw the same message(s).
Couldn't help but think about ur comment of xauto's design in post # 6.

kc2cbd · Dec 8, 2011

I just might play with this and see what I can come up with.

300ohm · Dec 8, 2011

Im puzzled by why it wont allow a 300 ohm impedance ?

And I guess vee boom and double boom lpdas would still have to be done in 4nec2s Geometry Edit.

holl_ands · Dec 8, 2011

7-El LPDA with Shorting Stub per LPCAD34 analysis was just posted to my website (see post#12 above):
http://imageevent.com/holl_ands/zigzaglpa
[Note that I reorganized the webpage, bringing LPDA's out from under the Zig-Zag LPA's.]

14-Element LPDA per Walter Dnes (9Sep2010) was also posted. It's a "Universal" LPDA
4nec2 file, with variable SYmbols, so user only enters BoomLength, F(low) & F(high) & number of Elements,
(which determines TAU).
The file is setup so that the number of elements can be changed. Can also run optimization scripts.
Note that 14-El LPDA has 300-ohm Characteristic Impedance, set by Crossover Feedline Impedance.

I did a few mods to Walter Dnes original submission, which can be found in this thread:
http://www.digitalhome.ca/forum/showthread.php?p=1151493
Note that this thread contains lots of references to LPDA design information.

I think the Raw Gain curves for the alternative Dual-Beam construction will be very close,
but you might have to model the actual boom and adjust the spacing to get the SWR spot on.....

kc2cbd · Dec 9, 2011

Here is one I just threw together using 300ohm's lpda.
UHF_LPDA_300ohm_CR_directors.nec

300ohm · Dec 10, 2011

That corner reflector and 3 directors doesnt do too much for it.

Dropbox looks good, 2 gb of free space for files. Cant you just move over the .nec file as is instead of a notepad file ?

DIY UHF log-periodic

Top Contributors this Month