Radio: Antenna analysis

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Radio: Antenna analysis

Postby Ian Law » Mon Dec 18, 2017 9:58 pm

I have a home made antenna, that is intended for use with a Yaesu hand held radio. Before connecting the antenna to the radio, I understand that it would be wise to use an Antenna Analyser to verify the integrity of my wiring and to check the "SWR" level. An SWR meter would be inadequate for this and an "Analyser" is needed. (Not that I have a clue about the electronics involved ).

I will have to remove the antenna and take it to someone who may be able to perform the test for me, since to buy the required kit would be uneconomic. ( = I'd love one, but can't afford it.)

Does anyone know of an expert within the ranks of the LAA, somewhere within reach of my Devon base, who may be able to help for a suitable fee?

Ian
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Re: Radio: Antenna analysis

Postby mikehallam » Tue Dec 19, 2017 12:23 am

Ian,

Unless your wiring and connectors are non standard there's no real pressure to SWR or whatever you're after. In any case testing a single component alone doesn't make sense. The a/c aerials one can buy are for the correct frequency band.

Or put your 'rubber duck' on the Yaesu directly - or remotely.

Failing that if you're determinedly DIY & want to make a 1/4 wave aerial - on a crossed Ali foil "ground plane" - use the mid frequency, say 127 MHz and calculate its length at approx 95% of a quarter of the wavelength at 300,000,0000 metres per second.

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Re: Radio: Antenna analysis

Postby JohnLindsay » Tue Dec 19, 2017 8:43 am

Ian,

A quick look on the Internet suggests that there are a number of Amateur Radio groups in Devon. Some 'Hams' (I believe they hate that term) certainly used to build their own equipment for mobile use in vehicles although today they probably buy it ready-made from Japan. Nevertheless, I would make contact with the local community because I bet there is an expert amongst them, with the necessary kit, who would love the unusual challenge of checking over an installation in an aircraft.

Just a thought.

John.
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Re: Radio: Antenna analysis

Postby Ian Law » Tue Dec 19, 2017 10:39 am

Many thanks Mike and John.

The only reason I chose to try a "DIY" antenna was to improve the performance of my basic hand held radio, in what will be a very noisy open cockpit aeroplane - assuming I manage to finish building it. The design was found on the web and discussed in depth on the EAA forum a year or two ago and appears to have found some favour among microlight pilots, who may have similar problems to deal with.

My light weight half wave dipole -- ( originally with a "Pawsey Stub" balun, but following a revision by the designer,now to be fitted with "Fair-rite brand #2631540002 ferrite cores" - see link etc. The Pawsey stub arrangement was the most difficult part of the project to make. The new "Baluns" will be very simple to install. ) -- was an interesting and easy project to make in the winter months when I couldn't do much useful woodwork in my ice box of a garage! ( see revised instructions: http://chrusion.com/public_files/InvVee ... s_rev3.pdf ) The reception appears to be perfect, as could be expected, but I can't yet test the transmission performance - and don't wish to risk damaging my shiny new radio. I assume that as long as nothing is shorting out in the wiring, I should be safe to go ahead, but it would be reassuring for an expert to verify all is well, before risking it. The revised, more conventional baluns, will much reduce the chances of shorting in the coax wiring, so I shall be a bit less worried about frying my radio.

I'll try the local radio "Ham" network and see if anyone in our local strut has any contacts who could help.

Thanks again ( & Season's Greetings)!

Ian
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Re: Radio: Antenna analysis

Postby jangiolini » Tue Dec 19, 2017 4:48 pm

Hi Ian, Firstly what is your aircraft constructed from? Secondly modern handheld radios are very robust their PA devices are designed to run with a huge mismatch. The one thing that they dont like is a short circuit.
The required test gear is a cheap ohm meter and a cheap SWR bridge(meter) a patch lead and the correct connectors to join it all together. I have been a Radio Ham for 45 years and build my own antennas never possessed and analyser!! The folded dipole with a pawsey stub is a nice antenna very broad banded but a little difficult to setup. I personally use a quarter wave vertical with a foil ground plane if its a wood or fiberglass aircraft and I tune the antenna for the middle of the transmitting band. The SWR (standing wave ratio) is just a measure of the forward/reflected signal and doesnt have a lot of effect on antenna performance. For reference if you transmit into a dummy load ie 50 ohm resistor you get a perfect match full power but no radiated signal!!!
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Re: Radio: Antenna analysis

Postby jangiolini » Tue Dec 19, 2017 5:07 pm

OK I was mid flow on my narrative when my computer decided to publish!! If you google a quarter wave antenna calculator you can enter the frequency you want and it will tell you what length to cut it. If you do go for a vertical use a tapered whip and make it as thick as possible! The thicker the whip the broader the band width(skin effect) also tapered whips dont bend so much in airflow. install the setup as clear of any vertical metal tubes etc as you can as they will effect the SWR as can transmitting in the hangar and give false readings. once installed connect the SWR meter and find a quiet frequency preferably mid band transmit and look at the reading then go to the band edges the variation will tell you if you are central. I wont go into interpretation of the readings as it will take too long.
PM me if you would like further information.
John.
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Re: Radio: Antenna analysis

Postby jangiolini » Tue Dec 19, 2017 5:18 pm

Hi Ian I just looked at the antenna (LINK) its really neat I dont think you will need to use a meter on it except to make sure you dont have a short in the building of it just use an Ohm meter. If you are very accurate on cutting the required lengths and I think you will be fine.
John.
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Re: Radio: Antenna analysis

Postby Ian Law » Tue Dec 19, 2017 5:56 pm

That's boosted my confidence John and thanks for all the advice.

I hope to modify the antenna over the next week or two, to use the revised ferrite baluns and perhaps to make some new dipole elements - the originals are a fraction of an inch short, since I used the wire that was available to me at the time. It will be much easier to make than the "Pawsey" design.

Thank you again!

Ian
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Re: Radio: Antenna analysis

Postby Ian Melville » Thu Dec 21, 2017 8:55 pm

Hi Ian,
1. the final test must be done in the aircraft out in the open or the RF picture will be all wrong.
2. A good quality VSWR is more than enough unless you want a performance check as well.

Though I do go to East Devon often, I am never there for long and you home airfield may be a bit too far. Unless you find someone closer, I have the kit to do a full band check if you are stuck.
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Re: Radio: Antenna analysis

Postby Ian Law » Thu Dec 21, 2017 11:33 pm

Many thanks Ian and I am grateful for your kind offer to help.

Although I'm progressing steadily with my building, there is still some way to go before my "Boredom Fighter" will be advanced enough to make an appearance at an airfield.

I bought the radio at this early stage to take advantage of the discount and the antenna was a winter project last year. I need to make up a fresh antenna coax with the ferrite baluns and discard the "Pawsey" arrangement. This should be quite easy.

I'll squirrel away all the information and finish off the radio set up this winter, with luck.

Thanks again for your advice.

Ian
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Re: Radio: Antenna analysis

Postby Ian Melville » Fri Dec 22, 2017 8:58 pm

No problem. Call if you need any help.
BTW I must post those PFA magazines back :oops:
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Re: Radio: Antenna analysis

Postby Ian Law » Fri Dec 22, 2017 11:14 pm

Many thanks Ian and hope the Magazines were useful. No great rush - whenever it is convenient for you.

Merry Christmas!

Ian
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