[UK-CONTEST] 80m antennas

Thu Apr 22 10:49:40 PDT 2010

Callum - there's no such thing as 'average-uk'. Ground varies from clay to 
sand to granite to . . . . within small distances.Geological maps helped me 
decide which house to buy when I saw that one is on the London Clay Belt 
(Thames) and the other wasn't.
73 de Roger/G3SXW.

----- Original Message ----- 
From: "Callum MØMCX" <callum at mccormick.uk.com>
To: "'UK Contesting'" <uk-contest at contesting.com>
Cc: <g3ory at lineone.net>
Sent: Thursday, April 22, 2010 3:28 PM
Subject: Re: [UK-CONTEST] 80m antennas

>>>> The exact figure depends on ground conductivity
>
> Ah-ha! I never thought of that. Yes, one would get a very different result 
> comparing a dry desert -vs- a wet ground!
>
> James got to grips with EzNEC but I stick with MMANA (unfortunately) so 
> the ground modelling isn't too good in that department.
>
> what do you think the real-world, average-uk-ground impedance would be at 
> say 20 feet for 80m?
>
> (I'll send to the reflector since this is good stuff)
>
> Callum McCormick
> t: 07976 631881
> http://www.m0mcx.co.uk/
>
>
> -----Original Message-----
> From: g3ory at lineone.net [mailto:g3ory at lineone.net]
> Sent: 22 April 2010 15:16
> To: callum at mccormick.uk.com
> Subject: Re:80m antennas
>
> Callum,
>
> Sorry to say that it does not work like that. It would, if the earth
> was a much better conductor than it actually is.
> You are correct in identifying that the mutual impedance between the
> antenna and the earth reduces the feed point resistance of the antenna.
> Since the radiation is proportional to current in the antenna and not
> to the power , there will be NVIS gain as a result. Unfortunately, the
> earth is an insufficiently good conductor to give the results you
> predict.  For a half wave dipole at resonance, the feed point
> resistance rarely drops below 50 ohms as the antenna is lowered towards
> the ground (recall it is 72 ohms in free space).  The exact figure
> depends on ground conductivity. Shorter antennas will exhibit lower
> resistances but don't have as much vertical gain in the first place.
>
> Try a bit of modelling to see what that tells you. Eznec does a
> reasonable job with modelling earth (a can of worms in itself) .  The
> differences in signal strength are not large and probably impossible to
> observe 'on the air' without having two carefully erected identical
> antennas (except for height) for comparison. Even then it would be
> pretty hard to tell the difference between an antenna at 50 feet from
> one at 75 feet.
>
> If you still don't believe me, then check out Fig 6.17 in Les Moxon's
> 'classic' book.
>
> 73 Bob
> G3ORY
>
>>----Original Message----
>>From: callum at mccormick.uk.com
>>Date: 22/04/2010 11:28
>>To: "UK Contesting"<uk-contest at contesting.com>
>>Subj: Re: [UK-CONTEST] QRS and QRP
>>
>>>>> I would rather use a "bent" 133ft dipole at 10ft than a G5RV at
> 40ft!
>>
>>Any horizontal antenna at 10 feet, certainly from half-size through
> to
>>double-sized) will outperform a similar antenna at 40 feet on 80m for
> NVIS,
>>close working. There will be negligible differences on gain for
> anything in
>>between. Be aware that if you really did run your 10 foot antenna,
> the
>>impedance would be around 4 ohms, hence most people aim for 25 foot
> plus -
>>just to get the impedance up to above 25 ohms.
>>
>>I guess you knew this anyway.
>>
>>Callum McCormick
>>t: 07976 631881
>>http://www.m0mcx.co.uk/
>>
>>
>>
>>-----Original Message-----
>>From: uk-contest-bounces at contesting.com
>>[mailto:uk-contest-bounces at contesting.com] On Behalf Of Rob - G4LMW
>>Sent: 21 April 2010 22:42
>>To: 'UK Contesting'
>>Subject: Re: [UK-CONTEST] QRS and QRP
>>
>>Tom
>>
>>Was your QRS station at the top end of the section (3560+-) - the
> designated
>>
>>"QRS Corral"?
>>
>>Like Danny, I always slow to the other station's speed, so I am
> surprised at
>>
>>his experience. Please encourage him to give it another try.
>>
>>On the antenna front, a G5RV is certainly not the best option and
> the
>>radiation angle of a vertical is probably worse (in most "skip"
> conditions).
>>
>>An 80 loop, longwire, or 80m dipole would be better.
>>
>>I would rather use a "bent" 133ft dipole at 10ft than a G5RV at 40ft!
>>
>>73, Rob
>>G4LMW
>>http://www.G4LMW.co.uk
>>
>>
>>
>>----- Original Message ----- 
>>From: "Danny Higgins" <danny.higgins at keme.co.uk>
>>To: "'Thomas Cannon'" <tom.g0vqr at ntlworld.com>; "'UK Contesting'"
>><uk-contest at contesting.com>
>>Sent: Wednesday, April 21, 2010 9:51 PM
>>Subject: Re: [UK-CONTEST] QRS and QRP
>>
>>
>>> Tom,
>>>
>>> I always slow down if I am called by a QRS station because I want
> to make
>>> sure he gets the call and the report correct.  Also, he may come
> back
>>> again
>>> in the next contest.
>>>
>>> I use QRP for CW and DATA when conditions are good, as 100W to 10W
> is the
>>> same as S9+30 to S9+20.  I use a full size 80M dipole up about 40
> feet and
>>> in the last CW contest I managed to hold a run frequency for over
> an hour.
>>> It helps to have a low noise level to pick up the other QRP
> stations who
>>> call.  I'll probably be QRP in tomorrow's data contest as I can
> only run
>>> 50W
>>> in data modes, so only disadvantaged by 7dB this time.
>>>
>>> Danny, G3XVR
>>>
>>> -----Original Message-----
>>> From: uk-contest-bounces at contesting.com
>>> [mailto:uk-contest-bounces at contesting.com] On Behalf Of Thomas
> Cannon
>>> Sent: 21 April 2010 21:14
>>> To: UK Contesting
>>> Subject: [UK-CONTEST] QRS and QRP
>>>
>>> I was approached by one of the members at are Radio club the other
> night
>>> who
>>> has just started to go into the Club Championship contests. He has
> never
>>> been in Amateur Radio contests before so was not sure of the QSO
> format.
>>> He
>>> also is learning Morse Code and was keen to try it out in the
> contest.
>>> I explained the use of cut numbers in contest N - 9 and T - 0 and
> the
>>> contest QSO format. which he was fine with.
>>> The problem he had this month in the CW  leg was that only 1
> station out
>>> of
>>> the handful he worked slowed down so he could understand them. I
> have been
>>> trying so hard this year to get members to take part in the Club
>>> Championships especially the members that are not contesters and
> the ones
>>> learning Morse Code.
>>> His comment to me was:" I am not sure I will do that again, only
> one
>>> person
>>> would slow down". If we want newcomers to take part in these
> contest we
>>> must
>>> slow down to their speed. I have convinced him to give it another
> try, so
>>> please if you are sent Morse very slowly, please send it back
> slowly to
>>> the
>>> other station.
>>>
>>> Also congratulations to some of the QRP stations in the Club
>>> Championships.
>>> There were some big scoring logs and I wish I had a station as good
> as
>>> theirs! I think the antenna must be the most important part of the
>>> station.
>>> I use a full size G5RV at about 30 feet and when the weather
> permits I use
>>
>>> a
>>> 40 metre verticle on a Helikite with 16 - 20 Metre ground radials.
> If
>>> anyone
>>> has any better ideas for an antenna on 80 Metres I would love to
> hear
>>> about
>>> it.
>>>
>>> Work you in a contest soon
>>>
>>> Tom G0VQR
>>>
>>>
>>>
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>>
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>
>
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