Log-Periodic Antenna Design

Before you get too far, be sure you know what you need. This is based on post 2/09 channel assignments. You will need to cover either a) CH2 - CH51 b)CH7 - CH51 c) CH14 - CH51

Tam

Most of the wideband TV antennas I've seen, seem to be log-periodic in the VHF range, but to use a reflector and a bunch of auxiliary elements (which don't appear to stick to the L-P taper schedule) for the UHF.

You might want to consider a different approach - have you seen this one?

--
Dave Platt                                    AE6EO
Friends of Jade Warrior home page:  http://www.radagast.org/jade-warrior
  I do _not_ wish to receive unsolicited commercial email, and I will
     boycott any company which has the gall to send me such ads!

snap:

Are you seriously THAT hard up for cash? :->

Try this - go to your local hardware or whatever store that sells a suitable log-periodic antenna with camera and tape measure in hand. Record it all and then go home and duplicate. Or easier still, buy it, take home, duplicate, then return for a refund.

Dave.

It's not log periodic but it looks cheap to toss together and they claim great performance:

----- Regards, Carl Ijames

snap:

You don't really need a new antenna. If your current antenna is working such that you get a good picture then it should work as a digital tv antenna.

Another Dave

Reminds me of the famous, very expensive Dick Smith Electronics Coa-Thanger antenna.

John

Interlibrary loan is your answer. Your library may not have it, but someone else's does.

Looking for a cookbook design, or the theory to do it yourself?

This won't do at all! Two of my favorite stations are ch. 56 & ch. 58. =:-O

I've got 2-13 covered by my external VHF folded dipole. (It's an RV).

Are the channel frequencies going to be all changed around? I suppose I should email those two stations. I don't know much about DTV, other than I have to buy a damn box and I need a "better" antenna.

Thanks, Rich

Thanks, but that thing's HUGE! I was thinking something more along the lines of 1' square. (or a 1' cube)

Thanks, Rich

I've heard that there's no "signal strength" meter or anything - it's either there, or not. With my analog, I can zero in on the proper tuning (I just futz around with the clip lead until it's "good enough") so I need something I don't have to screw around with.

Thanks, Rich

You probably don't need a program, just a decent text book that covers the topic adequately, which, undoubtedly is what the program writers worked from, and they might not have got it right! 'Antennas' by John Kraus contains enough detail to make a start and it's probably more general than someone's program which might involve specific choices of some parameter values. So my recommendation would be to find a technical library that offers access to non-members and send yourself to Log-Periodic School as you put it. The IET library in London does this, for free. Do you have an equivalent institution (e.g. IEEE), or a local university that covers electronic engineering? You might be surprised how much access you can gain to libraries to which you have contributed through taxes, or which need to maintain an 'altruistic' public appearance.

The pyramidal form has greater aperture in the vertical plane for all but the highest frequencies. It behaves like a vertically-stacked pair of Log-Periodic Dipole Arrays and achieves a bit more gain. Its pattern in the vertical plane is consistently sharper over a range of frequencies because of the vertical taper, but it is a bit more difficult to design. Not all 'wideband' UHF antennas are based on the LPDA - some are Yagi-Uda arrays designed using NEC and its derivatives, achieving a useful compromise between bandwidth, gain, and pattern shapes. But if you want to include channels below 21 as well as the UHF band, with consistent directivity, then LPDA is probably the only way to go.

Chris

Not after The Big Day. Their frequencies will be changing. Channels which are broadcasting NTSC in channels 52 and above will be moving down to a lower frequency.

A lot of them will be.

Take a look at:

I don't think it's the latest set of assignments but it's pretty well up to date.

--
Dave Platt                                    AE6EO
Friends of Jade Warrior home page:  http://www.radagast.org/jade-warrior
  I do _not_ wish to receive unsolicited commercial email, and I will
     boycott any company which has the gall to send me such ads!

Most digital STB's have a "signal strength" indicator on screen for each channel.

That's true of the displayed picture, but not the signal. Poor (or even too much) signal strength can lead to "drop outs" or "freezing" of the video image.

Dave.

Yes. Channels will vary depending upon your country and location. You should have some sort of official digital TV website for your country that lists and explains all this stuff. Australia for instance is:

(server down?)

Dave.

)

I agree. How much can a coat hanger cost? If you are really rubbing pennies together, I would ditch the log- periodic approach and go with something simpler, like a monopole or folded unipole antenna. (All you need is wire.)

I just want to mention (again) here that: Hopefully, we'll be able to knock out Ch-5 and Ch-6 from this antenna scenario very soon (and move them to the FM Band, as the FCC is presently considering. I'm a huge proponent of this possibility!

I will try to find the Comments link at the FCC web site so those of you who agree can chime in....

This idea has been floated before, of course. This time it seems to have "legs". I don't know how much you can read into it, but... the FCC has yet to explain how Non-Commercial Educational (NCE) vertical only stations can obtain authorization for horiz/vertical operation once this DTV transition occurs - which is now less than 90 days away.

There are many pending Construction Permits (CP's) and NCE facilities that proposed Vertical-Only operation in order to protect local ANALOG TV-6 stations. These new NCE facilities will undoubtedly delay construction until a decision is made how to obtain dual polarization licensing. (Due to increased transmitter power requirements and/or RF Safety exposure issues, tower height requirements, etc..)

To date, the FCC has yet to adopt ANY relaxed TV-6 digital protection criteria for NCE FM stations. Instead, these stations must use the old Analog standard - which is MUCH stricter than is necessary to fully protect a Digital TV operation!

And of course, there are only (8) full service TV's on digital channel

1. (Which is a really, really good reason to move TV-6, and possibly TV-5 to the FM band!! -- What a huge waste of spectrum!!) Yes, there are some low-power DTV 6's out there (translators, boosters, LPTV's). Not very many, and all of which are in locations where other spectrum is, or will be, avaialble after the DTV transition...

Anyway, any NCE or CP not near a digital-6 would obviously qualify for dual-polarization. It remains to be seen what the FCC will do about this. Hopefully, they will grow a brain and shift this "un-used" spectrum to alleviate the very crowded FM band.

I don't know if I should hold my breath or not.?

-mpm

Oops. that post was directed at Rich. My apologies for responding at the wrong thread entry point...

LOL ... talk about trolls! That HAS TO BE THE BEST TROLL OPENING LINE I HAVE EVER SEEN!

Well, that is the second best ...

hmmm ....

Ever heard of amplifed rabbit ears?

Regards, JS

Try a bowtie (like the one that came with sets) 5 inches in front of a piece of hardware cloth. Most of the boxes (which are almost free after the FCC rebate) have a signal strength bar (although with a 3-5 sec. delay)

Years ago they used to make one as a magazine rack that you could pick up and move around.

It's not a troll. I bought a fair good UHF-VHF antenna, assembled it and sat it on a saw horse in the driveway for test, and it tested perfect for 3 channels + ch.34 . So I set her up using a roof mount and LOST ch.34, and no amount of rotating got it back. (I was a pro antenna/tower installer as a kid).

Next I'm going to tape wire on 1/8" panelling and do experiments ... ugh, I hate trial and error. Ken