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Optimise that Peking Duck

Optimise that Peking Duck.

Those that know me will be aware of my opinions of hand held rubber duck only activations, but if that is what people want to do then good luck to us both. I will still chase you but the chances of a contact are minimised. There are however some issues with the rubber duck antennas on those cheap Chinese rigs that a lot of you are using. I have made a suggestion in a letter sent to Radcom. I don’t know if it will be published but I have put it on my web site for everyone’s perusal. I would appreciate any feedback including any additional information that might be a useful addition to the web page, including links. Digital photographs of your Chinese handies that I can use (copywrite free) might be useful too.

The article is here…
http://GW7AAV.googlepages.com/chinesehandheldradios

My email is correct on QRZ.com

Thanks Steve GW7AAV

In reply to GW7AAV:
Interesting letter Steve…

The problem I have is that when I connect anything other than the rubber duck to my Yaesu VX5 (more Sashimi than Duck I suppose), the front-end just gives up completely if there is a sniff of RF somewhere else in the spectrum. Do the Chinese hand-helds have an equally vulnerable front-end of do they fare better?

73 Marc G0AZS

In reply to GW7AAV:

Nitpicking but I think rather than just trimming the length for the best match you would be better using a field strength meter and analyser and trim for best match consistent with best detected field strength.

My dummy load is a fantastic match from DC to > 1.5GHz but that doesn’t mean it’s a good radiator!

G0FTD did a good article (linked via Southgate ARC site) for a 10m duck for the FT817. I’m sure that would make a good base for a variety of gainy ducks for 6m, 4m, 2m.

Other than that Steve, it’s a good article because it will force people to think that just because it’s commercial doesn’t mean it’s right!

Andy
MM0FMF

In reply to MM0FMF:

Hi Andy, yes I wasn’t suggesting just hacking away but a bit of prudent trimming with the antenna connected to an analyser can make a lot of difference. Hopefully it will have the desired effect.

Thanks for the tip. I will look into G0TFD’s article.

In reply to GW7AAV:

Here’s the link to G0FTD’s 28MHz duck:

http://www.southgatearc.org/articles/g0ftd/28mhz_rubber_duck.htm

Andy
MM0FMF

In reply to MM0FMF:

Cheers for the link Andy. I have just had a read of it. The design is very similar to the way I have made rubber ducks in the past for two metres and seventy centimetres. Instead of the flexible rod I use some hard plastic air tubing which is about the same diameter as RG-58. I then run some coax inner down the centre. The air tube fits nicely inside PL-259s designed for RG-58 or over the crimp type BNC connectors. I cover the lot with heat shrink, fit a strain relief boot, trim to resonance and add and end cap. The end caps come from fibre optic cables which I saved from binning some time ago, but you can buy similar ones. I have made red, black and blue rubber duck antennas. The red ones are 10dB better than the black or blue ones of course ;0)

I intend to do a web page with a step be step sometime so I may have a go at one for 28mHz and photograph it as I do it.

Steve GW7AAV

In reply to GW7AAV:
You mention antenna analysers. Something so expensive in relation to the number of times I would use it that I was putting off buying one till after we’ve repaid the mortgage in 2014. However my intermediate licence course tutor, Mike Street G3JKX, said any operator can have an analyser so long as it’s from a kit and he recommended the kit sold by South Coast Amateur Radio Club, Australia. Telford and district ARS ordered 10 sets of these [labelled as radio parts on the package ;¬D ] and they’ve been very satisfactory. When we visited Dave M0DFA to learn how to use his MFJ analyser, I was surprised how fast was the current drain. Dave switched his example off after every measurement. This Aussie design apparently performs better in the battery department.

Antenna Analyser kit is here at £74.52 today’s price and :- http://users.on.net/~endsodds/analsr.htm and one has to write to kits@scarc.org.au to check availability. Graham Thomas VK5GCT replied to my inquiry and has stock to sell. Paypal is used to order them.

http://www.spirat.com.au/vk5zvs/pic11.htm shows one built and modified for 6m band.

Would this be of interest to SOTA people ? No doubt one of you fine folks will digest the immense amount of data on the kit website and give it a critique.

Back to the crispy duck topic. I’m placing my trust in the J-pole recipe on Summitsbase for the first antenna to go with my shiny, new Wouxun KG699E for 70MHz. If Ann-Charlotte can drive me to the engineers’ merchants or a metal stockist one of these might be fun to try :- http://www.g0ksc.co.uk/4el-1457mtr-boom.html ! I think I might need my titanium-reinforced right leg just to haul it up the hills…

cheers
David M6WOW

In reply to M6WOW:

Something so expensive in relation to the number of times I would use it

You find that you end up using them much more than you would think. In which case the cost / benefit analysis rapidly changes from

“How much!!!”

to

“Why oh why oh why oh why did I put off buying one of these for so long!”

:wink:

Andy
MM0FMF

In reply to M6WOW:

The thing with antenna analysers is that you miss out on all the fun of standing in the rain & wind in a deserted field, trimming your antenna for the best VSWR :wink:

Seriously, I have been tempted to purchase one, but mainly for VHF / UHF, I still prefer the old fashioned method above for HF :wink:

As for the 4M J-Pole antenna to go with the Wouxon, I can highly recommend it. I built mine from the sort of non-slotted, translucent 300 Ohm feeder you can purchase at Maplin & it worked first time. I do believe others have not been so fortunate & have not had any luck, so be prepared for some possible experimentation.

I’ll have to take some close-up photos of mine, so you can see how it’s put together, but the dimensions are exactly as stated on Summitsbase.

In Reply to GW7AAV:

A very nice article Steve, & I hope it is published. A rubber duck will always be a compromise, until you get into 70cms & above where they can be full size quarter wave radiators, or even offer some gain over a dipole. I have nonetheless been very impressed with the rubber duck supplied with my Wouxon KG699E, but when I use it on a summit I would always use a J-Pole taped to my fishing pole, or at the very least a quarter wavelength telescopic whip. The rubber duck would be for very local contacts or experimentation only.

I’d have to save up & be sure of surviving the current credit crunch before I’d splash out on an antenna analyser though :wink:

It would take all the fun out of things. HI!

73,

Mark G0VOF

In reply to M6WOW:

Antenna analysers are expensive and that is why I suggest people join a local club who may have one or ask around. The Aussie kit looks like a great project (or club project?) and would no doubt give a lot of satisfaction to anyone building it. It is unfortunate that it only does HF. Even the mod only takes it to 6 metres.

The MFJ we have at the Mold & District AR club does up to UHF which makes is somewhat more useful for rubber ducks on hand held sets. I agree the MFJ analysers are power hungry and we always remove the batteries when not in use. The case design means you need a screwdriver to change the batteries so it is a pain. I also found using a power adapter with the MFJ was limiting and it seemed to mess up the grounding which slightly affected the measurements as does holding the analyser. I always place the instrument on a wooden or plastic table when I use it.

Having an analyser that works at UHF means you can try model antennas. I recently built a Moxon rectangle for 70cms for that reason. Quite often MFJs sell for around £100 second hand on eBay, Junksale and Richard CWI’s Flea Market so they don’t have to be much more expensive than the Aussie kit mentioned above.

On the subject of beams, I just bought a 70mHz Jaybeam as new in the box (pity they don’t do amateur aerials anymore) . It is one of their almost portable antennas. It has wing nuts and it all folds up on its self but the boom is 12 feet long, so I won’t be carting it up any hills soon. As I now have a spare 4m rig I might try using the AKD to give me a bit more power though.

In reply to G0VOF:

You can still stand in a wet and windy field with an analyser if it is battery powered ;0)

Regards Steve GW7AAV

In reply to GW7AAV:

I did a bit of Googling and found the following formula for calculating the number of turns for a normal mode helical antenna.

Turns = ( 2299 / ( F * D ) ) ^ 1.25

where F is the frequency in MHz and D is the diameter in centimeters.

The answer comes close to the G0FTD design. So it’s a suck it and see formula but should get you into the right ballpark if anyone wants to try making their own 10/6/4m antennas.

Andy
MM0FMF