[OZAPRS] Quadrant aerial

[Gerard Hill]

Thanks, Ray.

 From 1, the balun takes you from 50 ohms to 200 ohms, then the Q 
section with 1100 ohm line transforms that up to 6050 ohms. I expect the 
impedance of a Wells' quadrant aerial would be something like that of a 
full-wave doublet i.e. 2000-6000 ohms, so you'd need some way to adjust 
the matching. With (1), you'd need some way to keep the Q section 
physically stable over the full 7m length. You could adjust the 
separation of the wires for a good match.

With a Delta match (2), I'm not sure of your concern. A T-match is 
better anyway - more balanced. One advantage is that it's adjustable.

As for (3), I've been considering building a big J-pole for 30m using 
300 ohm ribbon for the matching and antenna. Have started on a 20m 
version to see how it goes. Had not planned on the 4:1 balun - just a 
direct coax connection with a choke on the outside of the coax. One 
issue is that a lot of height is needed so I plan to support the 20m 
version using a kite during testing.

An ATU (5) would not cope with the high impedance of the quadrant 
without assistance, it seems.

Option (6) is still a good one. Could also try a vertical dipole if you 
have the height.

Maybe I got the expurgated version - or perhaps option (4) was too 
horrible to consider :-)

Cheers ... Gerard, VK2IO

On 12/12/2010 2:16 PM, Ray Wells wrote:
> Gerard,
>
> 1. My preferred (simplest) method is a Q-section to a 4:1 balun.
> However, that method is non-adjustable, except by changing the Zo of the
> Q-section. A serious disadvantage is that an 1100 ohm Q-section requires
> 2, 0.5mm wires spaced 2m apart - not very practical, to say the very
> least. There is enough vertical height to the antenna feedpoint to
> cascade two Q-sections, to perform the impedance match in two steps but
> I haven't done any math on that yet. I seem to remember some info on
> this in The Antenna Engineering Handbook by Jasik.
>
> 2. I have pondered over Delta matching but have not yet extended that to
> any practical application. I can't get my head around any phasing errors
> that might result from feeding the antenna away from the centre. EZNEC
> might be able to model that arrangement.
>
> 3. A grounded quarter-wave section (any Zo), with the 4:1 balun 'tapped
> up' from the grounded end (like the matching section of a J-pole) would
> be adjustable and has the advantage of providing direct grounding of the
> antenna to minimise precipitation static, etc.
>
> 5. An ATU mounted at the antenna feedpoint would provide a nice
> band-pass filter, in addition to any matching but, it needs a
> weatherproof enclosure and a cap capable of handling near 800V. I 'may'
> have something suitable ex some long pensioned off military gear.
>
> 6. Of course I could throw my hands in the air and stick with my
> existing dipole and balun. My knees would appreciate not having to climb
> the tower.
>
> Ray vk2tv
>
>
> On 12/12/10 10:38, Gerard Hill wrote:
>> How will you match it, Ray? Delta match or T match perhaps?
>> Maybe its discussed in Wells' article from 1943, but its hard to get
>> hold of without an IEEE subscription.
>>
>> Damien, I'm currently using an end-fed inverted L antenna for 30m
>> APRS. Originally it was designed as a 3/8λ for 160m like this one:
>> http://www.n8mr.com/topband.html
>> I've shortened it to about 50m long so that its a 5/4λ on 40m and 7/4λ
>> on 30m. At 18m high, the horizontal length (32m) is less than an 80m
>> half wave dipole so it might fit your lot. Polarisation is mixed so
>> the vertically polarised local mobiles can be received as well as the
>> more distant stations via sky wave.
>>
>> Cheers ... Gerard, VK2IO
>>
>> On 12/12/2010 8:10 AM, Ray Wells wrote:
>>> With EZNEC the various wires have to attach to a single segment that
>>> contains the source. As I understand it, the NEC engine can't handle
>>> multiple wires attached to the source, hence the single, centre segment.
>>>
>>> I haven't looked at fan dipoles in EZNEC yet, I'm too busy trying sort
>>> out the Wells' Quadrant* for 30m.
>>>
>>> * Wells' Quadrant comprises two half-wave elements at right angles to
>>> each other at the feed point. The resulting radiation pattern is
>>> essentially omni-directional horizontal polarisation, within about
>>> 1.5dB, according to EZNEC.
>>>
>>> Ray vk2tv
>>>
>>> On 12/12/10 07:53, Damien Gardner Jnr wrote:
>>>> I'm thinking I got too technical.. either fan dipoles are completely
>>>> flawed, or antenna modelling just doesn't work on them.. I finally
>>>> finished putting the 20+10 dipoles in (lordy I re-learnt a lot of trig
>>>> last night!), and it looks absolutely horrid for SWR.. yet everything
>>>> I can find on the 'net suggests 1.5:1 on each band.. I might just
>>>> build it and see ;)
>>>>
>>>> --DG
>>>>
>>>> On 12/12/2010, at 6:30 AM, Ray Wells wrote:
>>>>
>>>>> Gee, I didn't get that technical <grin>
>>>>>
>>>>> Ray vk2tv
>>>>>
>>>>> On 11/12/10 23:51, Damien Gardner Jnr wrote:
>>>>>> Ewwww, ray was correct - swr on 30m would be 38 (609+j895) on 30m,
>>>>>> due to the other band dipoles not being full wave etc on 30m.. Ok,
>>>>>> will be a 40(+15)/20/10 dipole then ;) I had contemplated shoving 5m
>>>>>> on the bottom, but it might look kinda rediculous in the middle..
>>>>>>
>>>>>> --DG
>>>>>>
>>>>>> On 11/12/2010 11:35 AM, Damien Gardner Jnr wrote:
>>>>>>> ooh, really? I'm building one based from here
>>>>>>> (http://www.hamuniverse.com/multidipole.html) - yard isn't big
>>>>>>> enough for 40m of dipole for 80m band, so having already built the
>>>>>>> centre (http://www.rendrag.net/wpg2?g2_itemId=11755), I thought I'd
>>>>>>> just make the top band 40m, and add 30 in the middle.. Might shove
>>>>>>> it through MMANA first to see what happens, before I finish cutting
>>>>>>> and assembling that behemoth, and then pulling it up between the
>>>>>>> masts..
>>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>> DG
>>>>>>>
>>>>>>> On 11/12/2010, at 11:26 AM, Ray Wells wrote:
>>>>>>>
>>>>>>>> Previous experience of adding a 30m dipole to an existing
>>>>>>>> 20/40/80m unit was not good. 30m doesn't have a harmonic
>>>>>>>> relationship and it presented weird and wonderful reactance to the
>>>>>>>> feedpoint. ymmv
>>>>>>>>
>>>>>>>> Ray vk2tv
>>>>>>>>
>>>>>>>> On 11/12/10 11:19, Damien Gardner Jnr wrote:
>>>>>>>>> Lol, though monitors aren't allowed in bins, or even hard waste
>>>>>>>>> roadside pickup :(
>>>>>>>>>
>>>>>>>>> I have to say I do like the dell service, where if you order a
>>>>>>>>> computer with a monitor (can just be a laptop), they pickup the
>>>>>>>>> old monitor for free and dispose of it :) Though they had a heart
>>>>>>>>> attack when we asked if we could dispose of 60 21" sony's through
>>>>>>>>> that :-p Actually, they had enough of a heart attack when we
>>>>>>>>> asked about ordering 60 LCD's as 'spares' for our existing
>>>>>>>>> machines.. ;)
>>>>>>>>>
>>>>>>>>> -_DG
>>>>>>>>>
>>>>>>>>> Off to build a 40/30/20/10m fan dipole this arvo after work, will
>>>>>>>>> be interesting to see how much better that is than my TEV-1
>>>>>>>>> vertical!