[cma-l] AM v FM

Sun Dec 20 13:24:19 GMT 2015

I appreciate all the advice and input - thank you.
I have the huge advantage of having worked in an engineering laboratory that built VHF and UHF antennas and range-tested them so I am very fortunate to have an inbuilt comprehension of how they look and perform.
Nowhere in all that worthy information is there evidence of energy propagation patterns - actually measured in the field as opposed to calculated or computer modelled.
Most important - the difference between success and failure.
I can't guarantee to a Client how well an AM (MF) antenna will perform as I can with FM (VHF) - and that worries me.

Ian Hickling
Partner

Office: 01635 578435  (7am-11pm UK time)Carphone: 07530 980115 (only responds when driving)6 Horn Street, Compton, NEWBURY, RG20 6QS

From: geoff at susyradio.com
Date: Sun, 20 Dec 2015 02:50:23 +0000
To: cma-l at mailman.commedia.org.uk
Subject: Re: [cma-l] AM v FM

Just joining the discussion here on AM aerials.
You could also use an inverted L antenna, tuned to a quarter wave and an ATU to match it to the transmitter output.
These were very successfully used by the pirates of the 60s, 70s and 80s when strung between two high trees.  The vertical bit should be as long as possible and the earthing system was essential.  Rods and radials were the order of the day.  50 watts of RF power up the aerial used to get very good coverage up to about 15 miles if lucky.
Just my 2d worth.
Geoff
On 19 December 2015 at 16:05, Two Lochs Radio <tlr at gairloch.co.uk> wrote:

The top horizontal section is an active part of the 
deisgn as well as being a support for the main vertical radiator Ian. It 
essential forms one plate of a capacitor with ground.

It's a traditional (since before radio broadcasting 
began) design of shortened LF antenna. As I have always understood it, it's 
is essentially a vertical radiator, with a horizontal ladder across the top 
forming capacitive loading that allows the vertical radiator to be more 
efficient than it otherwise would be without being a full quarter-wave high. The 
radiation pattern is pretty much omnidirectional, regardles of the azimuth of 
the horizontal section over the top.

They are a good solution if you happen to have a pair of 
reasonably tall structures between which the horizontal section can be strung, 
such as Capital Radio's Lotts Road power station chimneys, or the Titanic's 
funnels.

Alex

  ----- Original Message ----- 
  From: 
  Ian 
  Hickling 
  To: The Community Media Association 
  Discussion List 
  Sent: Saturday, December 19, 2015 10:10 
  AM
  Subject: [cma-l] AM v FM

  By a "T-Antenna" are we referring here to a vertical radiator 
  acting as something approaching a bottom-fed quarter wave radiator held in 
  place by a horizontal "dead" wire on either side - or a horizontal dipole fed 
  by a vertical wire or line - or a combination of these?
It's important - as 
  propagation will be different in each case.
The antenna we will be using 
  for this project (dictated by land and funding available) will be a simple 6m 
  vertical pole using insulating stays, a capacitance hat and a loading coil in 
  the ATU at the base.
Efficiency will be about 8% - hence 1kW port output to 
  give 70W EMRP.

  Ian Hickling
Partner

  Office: 01635 578435  (7am-11pm UK time)
  Carphone: 07530 980115 (only responds when driving)
  6 Horn Street, Compton, NEWBURY, RG20 
6QS

  Date: Tue, 15 Dec 2015 22:26:56 +0000
From: tlr at gairloch.co.uk
To: 
  cma-l at mailman.commedia.org.uk
Subject: Re: [cma-l] AM V's FM

Sure 
  David, that's been a standard design for LF and MF antennas for over a 
  century. It is a vertical radiator with a capacitive top load to allow it to 
  be shorter, but it still depends on significant height to be efficient, and is 
  still a very big unwieldy structure compared to a half-wave VHF dipole stuck 
  up on a pole! 
As you say, the T ideally needs wetlands and in any event a 
  good earth system below. As I recall, when Capital Radio started up in London 
  they strung one between the chimneys of Lotts Road power station, and had the 
  advantage of being on the bank of the Thames for their earth. Most town centre 
  community stations won't have such a situation to hand! 

I think the 
  same sort of antenna design would have been on the Titanic - now that did have 
  a good earth plane below it!
Alex

  On 15 December 2015 at 14:55 Info 
    <info at transmittersrus.com> wrote:

    Ian, Alex,

    Look into the 
    T-antenna.

    They are 
    relatively low profile, do not requires huge swathes of the greenbelt and 
    are economically priced if you go DIY.

    Peter 
    ‘Chicago’ Murtha installed one just outside Walthamstow for the N. London 
    bible basher. One can see it a couple of minutes up the road from the dog 
    stadium.

    SMC among 
    others supply the hardware.

    Pitch it up 
    over some wetlands with a good ground system, buried or elevated and I 
    reiterate, you do not require anything like 800W of RF to meet that EMRP 
    quota.

    BTW, make sure 
    you have designed an efficient antenna tuning unit which can maximize the 
    bandwidth so you don’t sound like you have a pillow over the mic.

    David

_______________________________________________ 
  Reply - cma-l at commedia.org.uk The cma-l mailing list is a members' service 
  provided by the Community Media Association - http://www.commedia.org.uk 
  Twitter: http://twitter.com/community_media 
  http://www.facebook.com/CommunityMediaAssociation Canstream Internet Radio 
  & Video: http://www.canstream.co.uk/ 
  _______________________________________________ Mailing list guidelines: 
  http://www.commedia.org.uk/about/cma-email-lists/email-list-guidelines/ 
  _______________________________________________ To unsubscribe or manage your 
  CMA-L mailing list subscription please visit: 
  http://mailman.commedia.org.uk/mailman/listinfo/cma-l

_______________________________________________

Reply - 
  cma-l at commedia.org.uk

The cma-l mailing list is a members' service 
  provided by the Community Media Association - 
  http://www.commedia.org.uk
Twitter: 
  http://twitter.com/community_media
http://www.facebook.com/CommunityMediaAssociation
Canstream 
  Internet Radio & Video: 
  http://www.canstream.co.uk/
_______________________________________________

Mailing 
  list guidelines: 
  http://www.commedia.org.uk/about/cma-email-lists/email-list-guidelines/
_______________________________________________

To 
  unsubscribe or manage your CMA-L mailing list subscription please 
  visit:
http://mailman.commedia.org.uk/mailman/listinfo/cma-l

_______________________________________________

Reply - cma-l at commedia.org.uk

The cma-l mailing list is a members' service provided by the Community Media Association - http://www.commedia.org.uk

Twitter: http://twitter.com/community_media

http://www.facebook.com/CommunityMediaAssociation

Canstream Internet Radio & Video: http://www.canstream.co.uk/

_______________________________________________

Mailing list guidelines: http://www.commedia.org.uk/about/cma-email-lists/email-list-guidelines/

_______________________________________________

To unsubscribe or manage your CMA-L mailing list subscription please visit:

http://mailman.commedia.org.uk/mailman/listinfo/cma-l

-- 
Geoff Rogers
Programme Director
Susy Radio, Local Community Radio for Redhill and Reigate
On-air across Sussex and Surrey on 103.4FM NOW
Web: susyradio.com <http://www.susyradio.com>

Susy Radio Ltd. A company registered in England and Wales.
Registered Office: 54 Nutfield Road, Merstham, Redhill, Surrey, RH1 3EP.
Registered Number: 06748586

_______________________________________________

Reply - cma-l at commedia.org.uk

The cma-l mailing list is a members' service provided by the Community Media Association - http://www.commedia.org.uk
Twitter: http://twitter.com/community_media
http://www.facebook.com/CommunityMediaAssociation
Canstream Internet Radio & Video: http://www.canstream.co.uk/
_______________________________________________

Mailing list guidelines: http://www.commedia.org.uk/about/cma-email-lists/email-list-guidelines/
_______________________________________________

To unsubscribe or manage your CMA-L mailing list subscription please visit:
http://mailman.commedia.org.uk/mailman/listinfo/cma-l 		 	   		  
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.commedia.org.uk/pipermail/cma-l/attachments/20151220/62152afc/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: MF-Tee-Antenna.gif
Type: image/gif
Size: 4637 bytes
Desc: not available
URL: <http://mailman.commedia.org.uk/pipermail/cma-l/attachments/20151220/62152afc/attachment.gif>