[OZAPRS] Quadrant aerial

Tue Dec 21 08:20:44 EST 2010

Hi Ray,

I think you're right about the 'at height' adjustments - that would 
knock out a lot of matching mechanisms. With (3), the adjustment point 
is close to the ground and very simple - perhaps the best of the bunch.

Any reason for not wanting a vertical? If the ground plane can be 
eliminated then its pretty simple to set up. With the 30m J-pole, the 
height can be reduced by running the matching section horizontally. It 
doesn't radiate so there's no particular reason to having it vertical. 
The height is reduced to a half wavelength. Still tall for 30m, but not 
monstrous.

Cheers ... Gerard, VK2IO

On 16/12/2010 6:57 PM, Ray Wells wrote:
> 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
>
>