[Uram-rejections] Auto ATUs

Thu Aug 17 07:17:25 BST 2017

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

The post that you submitted to uk.radio.amateur.moderated has been rejected by a
moderator. 

Your message appears to the moderator to be abusive or hurtful to
another contributor.

The group charter and moderation policy can be found at
  http://www.chiark.greenend.org.uk/uram/
Disputed moderation decisions can be discussed in the newsgroup
  uk.net.news.moderation

============================================ Full text of your message follows
> From webstump at chiark.greenend.org.uk Thu Aug 17 06:11:06 2017
> Return-path: <webstump at chiark.greenend.org.uk>
> Envelope-to: webstump+?@slimy.greenend.org.uk
> X-Envelope-To: uk-radio-amateur-moderated at usenet.org.uk
> X-Forwarding-To: uk-radio-amateur-moderated at usenet.org.uk
> Delivered-To: forwarding-uk-radio-amateur-moderated at usenet.org.uk
> X-Virus-Scanned: amavisd-new at example.com
> To: uk-radio-amateur-moderated at usenet.org.uk
> From: "Jimbo" <kinvig.netta at ntlworld.com>
> Newsgroups: uk.radio.amateur.moderated
> Subject: Re: Auto ATUs
> Date: Thu, 17 Aug 2017 06:10:41 +0100
> Organization: A noiseless patient Spider
> Message-ID: <on388j$ios$1 at dont-email.me>
> References: <n9e0pc90vdum9cv58q25vmqnl2h0ft8qml at 4ax.com> <omvmnh$l8q$1 at dont-email.me> <1natocr.1veeqov1qxpmtcN%roger at hayter.org> <on2ksr$7c8$1 at dont-email.me>
> X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.6157
> X-Priority: 3
> X-RFC2646: Format=Flowed; Response
> X-Newsreader: Microsoft Outlook Express 6.00.2900.5931
> X-Auth-Sender: U2FsdGVkX1+4u8DqgfxSiKTj2bGx1XC51JlL9CQJOxs=
> X-MSMail-Priority: Normal
> Cancel-Lock: sha1:4+uWsPIflQpYZZH9hdt7Ik9dZEg=
> X-Gradwell-Message-ID: 14696437
> X-Gradwell-MongoId: 59952559.25f3-2340-4
> X-Gradwell-Forwarding-Rule: 1748292
> X-Gradwell-Edge-Server: inbound-edge-4.mail.thdo.gradwell.net
> X-Warning: 195.74.61.89 is listed at dnsbl.sorbs.net
> 
> 
> "Brian Reay" <no.sp at m.com> wrote in message 
> news:on2ksr$7c8$1 at dont-email.me...
> > On 15/08/2017 23:45, Roger Hayter wrote:
> >> Jimbo <kinvig.netta at ntlworld.com> wrote:
> >>
> >>> "Guy G4DWV 4X1LT" <no-email at tardis.com> wrote in message
> >>> news:n9e0pc90vdum9cv58q25vmqnl2h0ft8qml at 4ax.com...
> >>>> I will be buying an auto ATU and am torn between an LDG or MFJ unit.
> >>>>
> >>>> The MFJ seems to be much better value for money, but I have heard
> >>>> about the MFJ build quality and what the letters MFJ have come to
> >>>> mean.
> >>>>
> >>> make a resonant antenna auto atu's are for the lazy ........
> >>
> >> I am not sure that bringing in the moral values of hard work and
> >> avoiding excessive idleness or pleasure into aerial design makes a lot
> >> of sense.  It is certainly true that resonant aerials are often the best
> >> choice, but whether a ATU is a good idea may depend on whether it is
> >> absorbing 10%, 90% or 99% of the applied power.   With intelligent
> >> assessment of efficiency and bandwidth non-resonant aerials can be just
> >> as effective in one direction at least.  Though usually less easy to
> >> rotate or steer.
> >>
> >
> >
> > Like Jim. you are confusing resonance and  matching. If you feed an 
> > antenna which is 'cut' to be resonant at a given frequency but then feed 
> > it at a point where the impedance presents the wrong load to the tx, 
> > feeder, then you will have both a high SWR and, unless the feeder has low 
> > losses, high feeder loss.
> >
> > Take a 1/2 Wave vertical. You can't just feed it with coax at the end, the 
> > impedance it presents is way too high. The antenna is resonant. You could 
> > 'cheat' and feed it with a gamma match in the middle, or cut it in half, 
> > (yes a dipole), but if you look at the I and V distribution you will seem 
> > my point.
> >
> > When you add a coil to the bottom of a 1/2 wave vertical, it is to make an 
> > 'autotransformer' which matches the high Z at the end of the antenna to 
> > the low Z of the coax. True, the extra L generally means a bit of a 
> > reduction of the element. Sometimes a parallel tuned circuit with a 
> > coupling turn(s) or coil tap is used for the same reason.
> >
> > Either way,  the resonant, radiating, part is the element.
> >
> > No ATU changes the element.
> >
> > (Some antennas change element lengths but that is not the same as an ATU 
> > chopping bits off/sticking bits on.)
> >
> >
> >
> how patronising ... 
> 
> 
> 
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1

iQEcBAEBAgAGBQJZlTT1AAoJEJ0q8Kb5p+MeT/wH/3ZeQWzu9oyr3cDeXIEBZ+mY
1jenvpjAYhJYWxmqu9YaG098ZYw9wo4raD/ZzMWYZh0/vnFgA1qrjBBgeN7Ahjd9
kmXqCTFD9XQgo8mDPqmQk9f05QvE9yYZKEjy7jh7hkaFIWdxXwEjkqZ0JM8hALNH
JX4yvZEIAL3ZELc3NGXuoyZNBO0MnRCi5Jgj9+OMjbW2dQH9Iy8SFdJuBGjsD8UD
kAXxbSE3O+Ehxjodij9DIEmOKiYhV1KFkNx9vI53hcW38460RDLFOsoUK4BqwgJq
J8kMeotXYyyDzrAtw+mzSrMjWkdaT4qSldVyQ1ZHToUSXv825GI+FJCDK8rlB78=
=Pnq1
-----END PGP SIGNATURE-----