Yet another bargain

Old Reflector
1

As you’re all no doubt aware, I’m one of these people who just can’t resist a bargain.
Last time it was the hand held GPS, this time it’s a very nice 2 Metre 7 element Yagi.

At £39.95 + £7 shipping, this is a steal. There are those amongst you who would cry “I could build one cheaper”, however IMHO, for £47 delivered, it’s hardly worth the effort.

With a gain of 12dBd and a boom length of just 60" , this antenna has a lot going for it.

http://tinyurl.com/4mhjhar

Interestingly enough, it would appear that Moonraker do the same antenna for £69.95 + £4.95 shipping. Note the two images and some of the text are identical.

Ordered mine…

Mike 2E0YYY

2

In reply to 2E0YYY:
“I could build one cheaper” :slight_smile:

3

In reply to 2E0YYY:

Sorry Mike, that’s not a bargain. The ZL special’s dual driven arrangement does bring a higher gain but I think 12dBd is optimistic. Or shall we say difficult to achieve in practice. Or probably not really true. Certainly not on a 1.5m boom.

You’d be much, much better making a DK7ZB design which is lighter and more suited to backpacking. With published performance data, DK7ZB’s 7 ele requires a 3m boom to get 10.6dBd gain. A figure I find much more believable. It also has a nice wide bandwidth.

If you look at what people use out pbackpacking you’ll not find many all aluminium designs nor designs from the 70s. There’s good technical reasons for that. Antenna design has come on massively in the last 3 decades. Not only with DL6WU and DK7ZB designs but with G0KSC’s loop fed yagis and so the ZL special is a bit like a Ford Cortina. Ubiquitous in its day but now really a museum piece.

YMMV.

Andy
MM0FMF

4

In reply to 2E0YYY:
Hi Mike

The ZL is a good compromise antenna, however like Andy said it can be a bit outdated! My biggest problem with the ZL is the fact that they are not hassle free! Mine gave me that much grief, I ended up buying a straight Yagi!

Mine is a 5 ele by Diamond but I think one of the elements is for matching so its more like a 4! The whole boom is under 1 metre in length plus at the time of purchase it was £45! http://wsplc.com/acatalog/Diamond_Yagis.html

Having said that building a Homebrew one is far more satisfying!

I’m sure that if you rig it in the right way then it will be fine Mike

Good Luck

Matt 2E0XTL

5

In reply to 2E0YYY:

I think 12 dBi is more realistic, Mike, wshich is still a good gain, it would be a reasonable beam for home use but a bit complex for portable and with a lot of windage. Note on the Moonraker ad that they quote 9.5 dBd for the 5-el version and 12 dBd for the 7-el version, its hard to see how you can get an added 2.5 dBd from an extra two elements and extending the boom by half a metre when doubling the length again and adding a further 5-el just gives you 2 dBi!

73

Brian G8ADD

6

In reply to G8ADD:

Yes Brian, the law of dimishing returns. I think as far as SOTA is concerned it is down to what can you carry and here there is a further qualification. Carrying the 7 element up a quickly accessed summit like Shining Tor G/SP-004 is reasonable, especially when you are intending to stay quite a while and make 100 QSOs as Mike does, whereas it is less reasonable to carry one up Scafell Pike G/LD-001 as it usually takes several hours to get there.

Another issue is where the summit is located and whether it is sheilded. Is it close to population centres? As Mike has demonstrated, you can get away with a dipole on summits like Shining Tor, but try that on one of the GW/SW summits in south-west Wales or even somewhere like one of the lower GM/SS summits, then you could easily get a sore throat trying to qualify the summit.

Horses for courses I say - take what is appropriate for the summit… and I agree with Mike, for those without the time and workshop facilities, £47 isn’t a bad price for what is on offer, even if the designs by Martin DK7ZB knock spots off the competition.

73, Gerald G4OIG

7

In reply to MM0FMF:

I have to agree with Andy 1.5m boom is way too short for 7 elements.

My ‘proper’ ZL Special going way back when the design was State of the art had nine elements on a four or five metre boom and a five element reflector. It was based on the design in ‘Out of Thin Air’. The wind loading eventually turned out to be too much and my rotator snapped. ;0)

Steve GW7AAV

8

I am currently using (borrowing) Richard G3CWI’s SB5 - 5 el SOTA Beam. He sold these in the SOTA Beams range of products for a while, but don’t think he does any longer.

Like the 3 el SOTA Beam, it is very lightweight, takes only a couple of minutes to assemble, and is very effective. 100 QSOs in 2.5 hours last night in the 2m activity contest, with 15 locator squares worked (IO64, IO74, IO80, IO81, IO82, IO83, IO84, IO85, IO91, IO92, IO93, IO94, JO01, JO02, JO03) and best DX being GI4SNA, 297km.

I now wish I had bought one while Richard was making them, but at the time the interest was solely in Jimmy and I qualifying SOTAs on 2m, so the existing SB3 did the job perfectly and took only seconds to set up.

What is clear to see, is that Mike has a knack of optimising his station to make large numbers of QSOs on VHF - so I am confident he will get the best out of his new aerial.

Tom M1EYP

9

In reply to M1EYP:

Like the 3 el SOTA Beam, it is very lightweight, takes only a couple
of minutes to assemble, and is very effective. 100 QSOs in 2.5 hours
last night in the 2m activity contest, with 15 locator squares worked
(IO64, IO74, IO80, IO81, IO82, IO83, IO84, IO85, IO91, IO92, IO93,
IO94, JO01, JO02, JO03) and best DX being GI4SNA, 297km.

Very impresive, Tom. Well done on 15 locator squares.

I now wish I had bought one while Richard was making them, but at the
time the interest was solely in Jimmy and I qualifying SOTAs on 2m, so
the existing SB3 did the job perfectly and took only seconds to set
up.

Must admit Tom, setting up quickly is a doddle with the dipole, setting up even a 5 element yagi is a pain… However, no pain, no gain.

What is clear to see, is that Mike has a knack of optimising his
station to make large numbers of QSOs on VHF - so I am confident he
will get the best out of his new aerial.

I’ll give it a bash this coming weekend if it’s delivered in time.

Regards
Mike 2E0YYY

10

In reply to 2E0XTL:

In reply to 2E0YYY:

All noted, Matt.

Having said that building a Homebrew one is far more satisfying!

There’s no denying that.

I’m sure that if you rig it in the right way then it will be fine Mike

Good Luck

Well, I’ll give it a try, should be interesting.

Mike
2E0YYY

11

In reply to G4OIG:

In reply to G8ADD:

Yes Brian, the law of dimishing returns. I think as far as SOTA is
concerned it is down to what can you carry and here there is a further
qualification. Carrying the 7 element up a quickly accessed summit
like Shining Tor G/SP-004 is reasonable, especially when you are
intending to stay quite a while and make 100 QSOs as Mike does,
whereas it is less reasonable to carry one up Scafell Pike G/LD-001 as
it usually takes several hours to get there.

You’re spot on Gerald. This should be a good compromise for summits such as Shining Tor, Gun, The Cloud. As for some of the harder summits, I’d think twice about Kinder Scout, let alone Scafell Pike :wink:

Horses for courses I say - take what is appropriate for the summit…
and I agree with Mike, for those without the time and workshop
facilities, £47 isn’t a bad price for what is on offer, even if the
designs by Martin DK7ZB knock spots off the competition.

The materials alone would probably cost way over £25. Traders are asking six quid for a dipole centre these days!

Cheers
Mike 2E0YYY

12

In reply to 2E0YYY:

A cheap and cheerful antenna that I intend to try was published in a PW freebee in Nov 2004 (Antennas to go), a suspended quad loop using two lengths of bamboo, a square of wire (a two-wavelength loop), half a metre of 300 ohm ribbon and a trimmer for matching to coax. A friend uses one, it is of course bidirectional but has significant gain over a dipole, and you just roll it up over the bamboo to transport it.

I am a fan of dipoles and wide angle beams. Nothing is more frustrating to the chaser than to call a SOTA activator only to have him go back to somebody else, turn the beam and vanish. Sometimes they never turn the beam back to you, and you sit on the frequency getting more and more frustrated! This is why I have stuck to my dipole, I may not get out so far, but I won’t miss many callers!

73

Brian G8ADD

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In reply to G8ADD:

In reply to 2E0YYY:

A cheap and cheerful antenna that I intend to try was published in a
PW freebee in Nov 2004 (Antennas to go), a suspended quad loop using
two lengths of bamboo, a square of wire (a two-wavelength loop), half
a metre of 300 ohm ribbon and a trimmer for matching to coax. A friend
uses one, it is of course bidirectional but has significant gain over
a dipole, and you just roll it up over the bamboo to transport it.

I spoke to someone in VU on 15 Metres last year. He was using an antenna constructed from bamboo.

I’m a big dipole fan too. Throw it up in seconds, call CQ and away you go.

Mike 2E0YYY

14

In reply to 2E0YYY:

I spoke to someone in VU on 15 Metres last year. He was using an
antenna constructed from bamboo.

It would have worked far better if he used a conducting material such as copper wire.

15

In reply to G3CWI:

Double rim-shot!!

73

Brian G8ADD

16

In reply to G3CWI:

Yes in the old days my bamboo based hf quad did ok but the fibreglass version I now use is a lot better. Maybe because it is lighter, the “impedance” is lower. ;>)

73

Reg G3WPF

17

In reply to 2E0YYY:

The materials alone would probably cost way over £25. Traders are
asking six quid for a dipole centre these days!

Well, each to his or her own - I bought a SOTAbeam 2/70 when I was getting back into amateur radio, but have built all my antennas subsequently. There’s no need to buy a dipole centre for a home-brew antenna.

B and Q stock 6mm raw aluminium tube (don’t use the anodised version) for about £2.50 for a 1m length. It’s easy enough to extend this to a bit over 1m for the reflector by using a bit of steel screw to add on an offcut from a director!

They also stock plastic tube, which I use as the dipole centre, with the dipole elements a tight push fit. (I’ve used 8mm tube for the dipole.)

A 3m length of 21.5mm overflow pipe for the boom costs a few pounds (just found it online at about £3 inc VAT). If you need something collapsible, that pipe fits neatly into black electrical conduit; use a 40mm screw to hold them together.

You need a few rubber grommets to hold the elements centrally in the boom. For the dipole feed, drill 4mm holes through plastic and metal to take 4mm plugs. Or put screws through and attach croc clips as with the SOTAbeam (though if you use screws you then need to take one screw out to disassemble the antenna).

Use a balun of some kind (even the choke type as for the SOTAbeam) on the feeder.

Certainly not “way over £25” but under £25 - and I’ve found the DK7ZB designs great. My DK7ZB 7-ele for 2m has a boom that’s 3.3m long though, which is a bit much for SOTA - I normally prefer to take my DK7ZB 5-ele which has a 1.5m boom. Cheaper too!

I find the 7-ele a bit “pointy” for SOTA use, though it’s nice to have the extra gain for contests - but it’s not that much more gain than the 5-ele (less than 3db - half an S point!) which is why it doesn’t go out a lot. The extra length is also more of a nuisance especially in a wind.

None of these designs for short Yagis (and the 3m boom is a short Yagi!) have a huge gain over a dipole of course - the 5-ele DK7ZB is 8.5dB better than a dipole. However I like to have a bit more gain and a bit more directivity than a dipole for SSB.

The best bit for me is the satisfaction in using something you’ve built yourself. I know that’s not everyone’s cup of tea but it’s the way I enjoy my amateur radio. A great hobby with room for all ways of doing things.

Good luck with the new antenna anyway!

73
John GM8OTI

18

In reply to M1EYP:

I am currently using (borrowing) Richard G3CWI’s SB5 - 5 el SOTA Beam.
He sold these in the SOTA Beams range of products for a while, but
don’t think he does any longer.

More’s the pity, but I think the SOTA “public” either didn’t feel the need for or weren’t prepared to shell out for a more complex antenna. Setting up 5 elements takes about a minute longer than a 3 element and IMHO is worthwhile. I set up 13 elements most activations as I’ve added 8 elements for 70cms to my SB5 as per the DK7ZB dual band design. Gives me time to get my breath back after the ascent!

73, Gerald G4OIG

19

In reply to G8ADD:

Nothing is more frustrating to the chaser than to call a SOTA activator only to have him go back to somebody else, turn the beam and vanish.

I wholly agree Brian. The knack is for the activator to remember (subject to summit brain-fade) to put calls out to all quarters before pulling the plug. Sometimes this is difficult to achieve if your battery runs out of power or you are about to expire with hypothermia!

Must admit I am tempted to build 4 stacked cross dipoles to see how it would work for SOTA, but haven’t found time to do it yet. Mounting them would be the problem. Maybe one day…

73, Gerald G4OIG