[OZAPRS] Quadrant aerial

[Ray Wells]

Hi Gerard,

It's probably just as well that I'm too busy with other matters to rush 
into how to feed the WQ antenna.

The biggest problem I see with an 1100 ohm Q section is, with 2m between 
the wires, how does it maintain balance. That arrangement really is 
impractical.

Re Delta matching, the antenna relies on phase quadrature between the 
two legs to produce omni radiation. I'm still trying to grasp the 
concept of offset feed. I may be worrying about nothing and, if I had a 
bit more time I'd probably be able to nut it out. It's not a priority 
for now. I do, however, want to get away from having to make 'at height' 
adjustments - such as the T-match.

I don't see any issues with an ATU outside of voltage considerations. 
It's still not my favoured method.

I must investigate cascaded Q-sections to see if I can achieve something 
more acceptable from a line construction perspective.

Space and height are not problems but I really don't want a vertical 
antenna. I did think about a ground plane at one stage but trees are 
cheap here and they don't need radials. A 30m J-pole? Now that would be 
a tall antenna.

Cheers ... Ray

On 16/12/10 04:48, Gerard Hill wrote:
> 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!
> _______________________________________________
> OZAPRS mailing list
> OZAPRS at aprs.net.au
> http://lists.aprs.net.au/mailman/listinfo/ozaprs