Log periodic antennas for VHF and UHF

[VK4WDM]

As a result of another of my threads I am seriously thinking about buying or making an LPA for VHF-UHF. Ideally it would cover 50-1300MHZ giving me coverage of the 6m, 2m 70cm and 23cm ham bands (and a 4m band if we ever get one) and could be used for my other interest which is the aviation bands. A light-weight LPA could be easily "flipped" for vertical polarisation if needed.

Yes, I know that an LPA is a compromise and won't rate with monoband yagis, but I not out to break records, just have fun, and keep a promise to my XYL that I would reduce the "unsightly clutter" of multiple antennas at our new home.

Tennadyne Antennas in the USA (http://www.tennadyne.com) have their model T28 which covers 50-1300MHZ and the the reviews about its performance and materials are very good. Price is listed at US$444. Comet have a similar antenna at about the same price but I doubt if the quality would match the US model.

There is the option of home brew. Paul VK4APN has sent me some plans for for a 2m and 70cm LPA that I intend to build for portable use, but does anybody have any plans for one that covers 50-1300MHZ?

73

Wayne VK4WDM

[VK4OX]

Wayne,
The answers to most of your questions are on the World Wide Web. Mr Google is your friend.

An LPDA designed for 50-1300MHz is possible but you will require a wide band Balun to feed it.. I've built an LPDA for 80-280MHz and I am very happy with it. To keep the SWR low across the entire band, I used elements with, as close as possible, a constant L/d ratio... 19mm diameter for the 80MHz elements and 3.2mm diameter for the 280MHz elements and various diameters for the in between elements. I checked the SWR only across the 144MHz band and it was less than 1.2:1. I designed the double boom for a 50 Ohm impedance and fed this with 50 Ohm coax with about 20 ferrite beads slipped over the end of the coax at the feed point.. That seems good enough over the 80-280MHz band I am using but it may not be good enough over the bandwidth you are contemplating.

My double booms are made from square Aluminium box section, 25.4mm x 25.4mm x 1.2mm wall thickness.. i think Capral sells this as Qbloc ( vy cheap). The two booms must be mounted parallel to each other with a gap of about 6.35mm between them over their entire length to maintain an impedance of 50 Ohms. I insulate the booms from the mounting mast by means of the familiar Poly-whatever breadboards, available in WoolyColes . Cost? about $50 -$100 but less if you have stuff lying around. US$440 for a commercial antenna seems like an expensive option to me. My antenna has been up for over two years now with no trouble.

Design data here:

http://glendash.com/Dash_of_EMC/Log_Per ... riodic.htm

73, Adrian. VK4OX.

[VK4FP]

Hi Wayne,
I designed a LPA for 48-450 Mhz..Worked well enough..VSWR <1.3 all bands.
Twin boom..Using a LPA Cad program.
Only has approx 7.5 dbi gain.18el , 1.8m boom length.
Don't expect miracles with them.However it has a great for BW.
Cheers,
Lloyd VK4FP

[VK4WDM]

Hi Adrian and Lloyd

Thanks for the ideas. The main aim at my station is to simplify things so that if we wake in the morning and decide to go travelling I can get the antennas down in a few minutes and have no need to worry about them whilst we are away. Also make things easier if a cyclone is looming

My Butternut HF9 vertical covers all the HF bands except 160m (but I am working on that) and if I add an LPA for VHF/UHF all my radio needs are covered with just two antennas (yes Barry VK4TI, I am still building a mag loop but that is for a different location).

The Tennadyne antenna may seem a bit expensive, but it is obvious that a home brew version is quite complex and time-consuming to make and optimise whereas the commercial one is just "plug and play", and the cost to me will be offset by the selling off of my existing antennas, so I have to weigh up both options carefully.

73

Wayne VK4WDM

[VK5PJ]

Hi Wayne et all,
many moons ago I built a LP for 28 - 55 MHz when I was mad crazy about the band during my time in VK8. Mine used the ATN style insulators that were common at the time and worked quite nicely for TV hunting.

You may want to consider splitting up your frequency coverage into smaller chunks on multiple LP's, this may give you more gain per spot frequency depending on the boom lengths you choose as the LP will not need to be so compressed to get the bigger frequency coverage of a single one. Then you would have the ability to have a low frequency LP pointed in a different direction to the UHF one.

I must admit the BALUN on mine is total crap as it was made from some no name ferrite core inside a 35mm film container so I need to revisit that now its back up in the air.

Regards,
Peter Sumner

[VK3APW]

Hi Wayne,
I have a 'bought' LPA that covers 6M to 23cm, it is a Creative Design CPL 5130 -1N, which I decided to use, as are you, for simplicity, rather than performance. I simply can't get enough height to clear the roof, maintain a stacking distance and stay under the 8m council restriction. In any case whatever the reason, I can tell you, that they work well enough on 6 , 2 and 70, but you will need to have a second thought about trying to use it on 23cm. The VSWR is quite high on 23cm at 2:1, also the pattern is not nice. At least on mine.
If you fit a triplexor, you will also get a fair degree of isolation between bands.
They also look very much like a TV antenna

Good luck

Cheers

Peter vk3apw

[VK4WDM]

Hi Peter

Thank you for your info on the CPL 5130 -1N. There is currently very little activity on 23cm so that does not worry me too much, but I got a huge shock when I got a price from an Australian supplier - close to $700 and the cost of shipping from the USA is much too high.

I have been in email contact with guys using the Tennadyne T28 who are extremely pleased with both the performance (even on 23cm) and the engineering. I have not heard from the company yet about the cost of shipping but I expect it to be also too expensive. That leaves the HB option but these are technically-challenging antennas.

I have had reasonable success with a 2m/70cm yagi mounted on the same boom and I might go down that same track again with a shorter length, lightweight materials (some G stations use 2mm rods for elements), and a single feedline with triplexers. I need to be able to drop the mast very quickly by myself if needed, so light and simple is important.

73

Wayne VK4WDM

[VK6LD]

Hi Wayne,

I just checked DX Engineering in the US sell the Create CLP-5130-1N (21 elements) for $469.95 and the CLP-5130-2N (17 element) for $343.95.

Freight on the 1N is $81.90 and freight on the 2N is $53.82. (All prices in $US)

I have always had good service with items purchased from DX Engineering. They typically arrive at my doorstep 8-10 days after ordering. Payments can be made with credit card or Paypal.

Hope this helps.

Cheers,

Rob...
VK6LD

[VK4WDM]

Hi Rob

Thank you for that. I never thought of DX Engineering although I have brought from them previously. If I go down the route of separate yagis and a single feedline I am going to need a triplexer at each end of the line and they are not cheap.

73

Wayne VK4WDM

[VK2VHF]

FYI, I just purchased a beam from DX Engineering and it arrived at my door in 3 days. Service was excellent.

(Local supplier said it would take ~2 months to get the same gear).

[VK3ALB]

Wow, you could buy an awful lot of aluminium and plastic and mounting hardware for that kind of money.

[VK3PY]

Indeed, Lou. For that kind of money you could not only buy the required materials, but equip your workshop with the necessary tools (bench drill etc.). I've always regarded the antenna as the easiest part of any project, and most satisfying to construct. Beats me why anyone would fork out that kind of money to forego the pleasure of building an antenna!

Chas
VK3PY

[VK4WDM]

Beats me why anyone would fork out that kind of money to forego the pleasure of building an antenna!

Depends on the circumstances I guess. Skill level, time-poor, or like me, increasing age and arthritis. I have been building antennas for close to 50 years and currently building a dual band 2m/70cm DK7ZB designed yagi and a super-lightweight 6m beam, but it is obvious that I am approaching a stage when such projects will be beyond me unfortunately

I think the other issue we need to remember in the cost of antennas is we are also paying for the research and development. My guess is that it would take a big amount of time to design, test, and commercially develop an LPA that will cover 50-1300MHZ. The military have similar antennas and they would be close to ten times the price of the ones on the ham market.

73

Wayne VK4WDM

[VK2VHF]

I agree with you Wayne.

I am keen "backyard" engineer and I have made many antennas too, but occassionaly I buy one simply for the fact that I cannot match the quality of a commercially made antenna. Just recently I bought a beam made by M2 in the US. The T-match block is high quality CNC machined and it is far superior to what I could build with bits and pieces from a hardware store and copious amounts of silicon.

Yes I do enjoy a challenge and learning from the experience - but not always.

Adrian

[VK3DXE]

I've also bought antennas where lack of time or workshop facilities (i.e. ROOM) has meant I couldn't build what I needed at the time. I'd much rather roll my own, but there are times when that just isn't possible.

There's also the aesthetics considerations of significant others and/or neighbours where a commercially made product stands out considerably less than a fugly-built homebrew unit.

[VK3PY]

[quoteDepends on the circumstances I guess. Skill level, time-poor, or like me, increasing age and arthritis][/quote]

Point taken Wayne. Just this afternoon I etched a printed circuit board and proceeded to drill it. Even with my X3 magnifying specs I confess that more than a few holes were a little eccentric - just like yours truly, I suppose.

Chas
VK3PY

P.S. No "fuggly" antennas here, though.

[VK4WDM]

Hi Chas

Nice bunch of antennas! Unfortunately the days of big arrays have gone for me. Small inner suburb block now, 8m height restriction, and the need to get the antenna down quickly unaided if required. That is why a 50-1300 MHZ LPA looked good, but as previous postings point out, they are pricey. I am hoping that a light weight 4el 6m yagi, the DK7ZB 2m/70cm yagi, and a very light 16 el 23cm loop yagi will do the job at much less money, and they are within my building capability

73

Wayne VK4WDM