WICEN Project Night - 5th February


(David Longland) #1

The Brisbane WICEN Group are planning to make a number of UHF/VHF dual antennas operating in the 2 metre (144 - 148 MHz) and 70 centimetre (420 to 450 MHz) bands. Members of HSBNE are welcome to join us. Each individual will be required to provide their own parts. A full parts list will be published shortly.

These aerials are described on the following web sites;

  1. www.barc.asn.au/resources/Antenna_Flower_Pot_2M_70cm_Dual_Band.pdf

  2. vk2zoi.com/articles/half-wave-flower-pot/

Regards
David Longland
VK4MDL


(David Longland) #2

The WICEN group have had to shift the date for their first project night to Monday 5th March.

If you are interested in radio communications please come along. If you are interested in building an aerial close to the frequencies shown above please let me know as we may be able to look at helping you.


(Stuart Longland) #3

Just a reminder, someone (who will remain nameless) did miss the discussion regarding the date at the last meeting…

The project night will take place on the 5th of March.

That’s next month, not tomorrow night. :slight_smile:

Edit: Main website announcement posted. https://www.brisbanewicen.org.au/2018/02/04/wicen-project-night-5th-march-2018/


(David Longland) #4

Below is the list of materials required. Please note that if you are interested in building an antenna near either 2m or 70cm wavelengths this may be possible to accommodate but would you please let me know. The links below will provide some background data on this type of antenna.

VK4MDL

2m / 70Cm Flowerpot Antenna

http://vk2zoi.com/articles/half-wave-flower-pot/

http://www.barc.asn.au/resources/Antenna_Flower_Pot_2M_70cm_Dual_Band.pdf

or Google the above heading.

Bill of Materials

· 25mm grey PVC Conduit x minimum 1260 mm long. Any other colour may require adjustment of measurements.

· 25 mm PVC conduit cap.

· RG58 coax cable (must have braided shield) x minimum 2mtrs – Jaycar WB2012 stranded core or WB2010 solid core.

· Antenna Connector of preference (suggest BNC female to allow connection to coax run without joiners) - Jaycar PS0660

· 39 mm diameter double wall heatshrink (to seal loading coil) (70 mm) ) – a luxury, otherwise leave bare. (Still trying to source, 17-1-18 VK4ZGB)

· 30 mm diameter double wall heatshrink (to seal 70Cm sleeve)(250 mm) – Jaycar WH5626 (1.2 M)

· 12 mm diameter double wall heatshrink (to seal BNC connector and coax at ends of coil) (100mm) – Jaycar WH5643 (1.2 M)

· Short length fishing line (to tension antenna inside PVC Conduit) appx 500 long. Someone should have this in their buggary box.

· Aluminium cooking foil, aluminium building sarking, brass shim or salvaged coax braid to cover 235mm of 25mm PVC Conduit

· Qty foam disks to centre antenna element inside conduit. A luxury and to maintain tuning of 70 Cm. We should be able to supply these.


(Nathan Beveridge) #5

Is the specification of ‘grey’ to do with that you have tuned one made with the conduit available in that colour before or is there some other magic/physics going on their?


(Stuart Longland) #6

I can ask… but I think it has to do with the other properties of the plastic pipe.

The different types of PVC pipe are colour coded according to their purpose, some are re-inforced with other materials which have an impact on their RF properties.


(Ashley Gittins) #7

On the website linked above the designer mentions factoring a 2% reduction in measurements to account for the grey PVC which I think is more dense than white PVC and thus has a higher dielectric constant.

From http://vk2zoi.com/articles/half-wave-flower-pot/

Using something other than grey electrical conduit
To the purist and his microwave oven, grey electrical conduit is considered lossy. It is, however, very UV resistant. The design compensates for the affect of the conduit by shortening the elements (by about a 2% factor) but otherwise the conduit appears to have little effect on the radiation efficiency.

If you use orange (HD) conduit, irrigation pipe, Telstra conduit, GRP, etc, the element lengths will be different. An unenclosed antenna will have longer elements (probably 2% or maybe 3% longer). Similarly, an antenna enclosed in something that is very much loaded with conductive filler will be much shorter (but, of course, don‘t ever use a material like this for an antenna).

IIUC, using a different dielectric will cause the centre frequency of the antenna to shift somewhat (~ more stuff = lower freq -> make it smaller to raise freq), plus you’ll probably need to adjust a bit more than you would otherwise to achieve the best SWR (which might not be as low as you could get with dimensions that account for the particular dielectric).

As with all things RF though, yes, it’s mostly magic.


(Stuart Longland) #8

Hi All,

Don’t forget, next monday evening 5 March at 7.30 pm at HSBNE Hamilton for our first projects night.
The project will be making 2M / 70cm flowerpot antennas.

Below is a BoM for one of these antennas to allow you to start sourcing your materials. There will be tools and test equipment on hand on the evening to ensure the antennas are appropriately tuned. Have a look at the links to get a “heads up” of the project. Any queries or questions to myself, and if I am able, I will give you a sensible answer.

This project is also being opened up to HSBNE members as well.

If anyone knows of a reasonably priced source of 39 mm dual wall heatshrink tubing, please let me know. We need approx 75 mm per antenna.

Catchya,

Gary

VK4ZGB

vk4zgb (at) gmail.com


2m / 70Cm Flowerpot Antenna

http://vk2zoi.com/articles/half-wave-flower-pot/

http://www.barc.asn.au/resources/Antenna_Flower_Pot_2M_70cm_Dual_Band.pdf

or Google the above heading.

Bill of Materials

  • 25mm grey PVC Conduit x minimum 1260 mm long. Any other colour may require adjustment of measurements.
  • 25 mm PVC conduit cap.
  • RG58 coax cable (must have braided shield) x minimum 2mtrs – Jaycar WB2012 stranded core or WB2010 solid core. We are planning to have a qty of this for purchase.
  • Antenna Connector of preference (suggest BNC female to allow connection to coax run without joiners) - Jaycar PS0660
  • 39 mm diameter double wall heatshrink (to seal loading coil) (70 mm) ) – a luxury, otherwise leave bare. (Still trying to source, 27-2-18 VK4ZGB)
  • 30 mm diameter double wall heatshrink (to seal 70Cm sleeve)(250 mm) – Jaycar WH5626 (1.2 M)
  • 12 mm diameter double wall heatshrink (to seal BNC connector and coax at ends of coil) (100mm) – Jaycar WH5643 (1.2 M)
  • Short length fishing line (to tension antenna inside PVC Conduit) appx 500 long. Someone should have this in their buggary box. VK4AL will provide.
  • Aluminium cooking foil, aluminium building sarking, brass shim or salvaged coax braid to cover 235mm of 25mm PVC Conduit. I will take along a roll of this.
  • Qty foam disks to centre antenna element inside conduit. A luxury and to maintain tuning of 70 Cm. We will be able to supply the material for these.

I actually asked Gary about the colour of the conduit, it’s to do with the concentration of carbon and other substances within the PVC, which all have an impact on the transparency to RF.

Basically, if you can put a sample of the material in question in a microwave beside a cup of water, and nuke it for a few minutes on high, and not have the sample heat up, then you’re good. If you burn your mitt picking it up, then don’t use it for an antenna.


(Stuart Longland) #9

Well, it went well. Full write-up is here:

https://www.brisbanewicen.org.au/2018/03/06/march-2018-project-night-flower-pot-antennas/

I’m not sure what’s planned for April as @vk4mdl and I will be away (getting as far away from the Gold Coast as we can), and there’s a good probability a number will be tied up with the upcoming Easter horse endurance ride, but we’ll see.