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Antenna tuning

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dpark748(at)hotmail.co.uk
Guest

Posted: Fri Mar 26, 2010 1:44 pm Post subject: Antenna tuning

I have just borrowed an SWR meter and am trying to tune my Comm antenna.  The manual says to tune by shortening until minimum reading at 127.50  I am getting Minimum reading at 133.00. My last two cuts of 3mm have not moved the minimum reading 1.5 at 133.00 above and below this frequency the readings are at 1.9 -1.9.

 Do I keep shortening the antenna????

 Any ideas?  Regards Dave Park  G-LDVO

 		 	   		    [quote][b]

jimpuglise(at)comcast.net
Guest

Posted: Fri Mar 26, 2010 1:59 pm Post subject: Antenna tuning

David- 

  

I assume you are talking about the copper strip antenna that comes with the kit.  My own approach is to start at the bottom of the band and record the SWR every 50 khz.  After you have done this, put the figures in Excel and graph it.  Each line in your Excel spreadsheet shoud have one frequency in column A and the SWR at that frequency in column B.  In this way, you can see what the antenna is doing through the entire band.  You need to be concerned that the SWR is not extremely high at one end and extremely low at the other.  I usually shoot for 1.0-1.2 / 1 at the center and 1.9 or so at each band edge.  If you are at 1.5 in the middle of the band, that should be just fine.  The reason you are not seeing change with small adjustments is that it is probably relatively flat a few MHZ each side of resonance.  Also, I don't know if you are using the coax that comes with the kit, but I took one look at it and threw it away.  Invest in some good RG-58 for the comm antenna and some RG-400 for the transponder.  When you look at the graph, it will be very obvious what you need to do.  

  

Jim Puglise A-283

 

---

dpark748(at)hotmail.co.uk
Guest

Posted: Fri Mar 26, 2010 2:13 pm Post subject: Antenna tuning

Jim,

 Thanks for that, yes I did use the coax that came with the kit - major job to change that now - unless it is worth making a connection in the tail area to the kit coax with RG58??

 I am just a bit concerned that if I keep cutting to achieve 1,5 at 127.5, presently 133.0 I might bxxxxx it up compleyely!

 Dave 

  Date: Fri, 26 Mar 2010 21:59:15 +0000

From: jimpuglise(at)comcast.net

To: europa-list(at)matronics.com

Subject: Re: Antenna tuning



  .ExternalClass p {;}    David-

  

 I assume you are talking about the copper strip antenna that comes with the kit.  My own approach is to start at the bottom of the band and record the SWR every 50 khz.  After you have done this, put the figures in Excel and graph it.  Each line in your Excel spreadsheet shoud have one frequency in column A and the SWR at that frequency in column B.  In this way, you can see what the antenna is doing through the entire band.  You need to be concerned that the SWR is not extremely high at one end and extremely low at the other.  I usually shoot for 1.0-1.2 / 1 at the center and 1.9 or so at each band edge.  If you are at 1.5 in the middle of the band, that should be just fine.  The reason you are not seeing change with small adjustments is that it is probably relatively flat a few MHZ each side of resonance.  Also, I don't know if you are using the coax that comes with the kit, but I took one look at it and threw it away.  Invest in some good RG-58 for the comm antenna and some RG-400 for the transponder.  When you look at the graph, it will be very obvious what you need to do. 

  

 Jim Puglise A-283



 ---

gregoryf.flyboy(at)comcas
Guest

Posted: Fri Mar 26, 2010 7:10 pm Post subject: Antenna tuning

> I am just a bit concerned that if I  keep cutting to achieve 1,5 at 127.5, presently 133.0 I might bxxxxx it up  compleyely!

 	  Quote: 	
		   Dave 


	


 Dave,

  

 Unless I am suffering from temporary dyslexia, I think you would  need to lengthen your antenna at this point, to get the SWR reading to come down  in frequency from a low reading at 133Mhz, since 133Mhz has a smaller wavelength  than 127.5 Mhz 

  

 regards,

 Greg Fuchs XS Tri

  

  



   

   [quote][b]

jimpuglise(at)comcast.net
Guest

Posted: Fri Mar 26, 2010 8:01 pm Post subject: Antenna tuning

Dave- 

  

Shortening the antenna raises the resonant frequency, lengtlhening it decreases it.  No, if it is a hassle, it would not be worth changing the cable.  If you do the graph, you will get a better picture of just where you are.  

  

Jim  



---

Bill & Sue

Joined: 10 Jan 2006
Posts: 48
Location: Malvern, Worcs. UK (Defford, Croft Farm)

Posted: Sun Mar 28, 2010 2:21 am Post subject: Re: Antenna tuning

Dave,



If you are anywhere near me (Aylesbury, so must be closer than Ferg!)) I'm happy to turn out and provide some hands-on help if you think that would be useful. I suffer from the delusion that I know a little about antennas (antennae?) and I have a couple of suitable SWR meters and some practical experience messing about with this sort of antenna. Please give me a call on 01296 689165 if you think that would be any use or you just want some telephone advice.



Regards



Bill

dpark748(at)hotmail.co.uk
Guest

Posted: Sun Mar 28, 2010 3:34 am Post subject: Antenna tuning

Bill,

 Thanks for the offer but I am in South Manchester, nr airport!. But I may ring you when I am next in the garage. Originally with the length at 490mm as per drawing the best SWR was at 133.00. I shrortened it down to 480mm but could not get best SWR mid frequency range. I have temporarly extended the antenna to try again.

 Regards Dave 

[quote] Subject: Re: Antenna tuning

 From: Billandsue(at)billbell.co.uk

 Date: Sun, 28 Mar 2010 03:21:15 -0700

 To: europa-list(at)matronics.com

 

 --> Europa-List message posted by: "Bill &amp; Sue" <Billandsue(at)billbell.co.uk>

 

 David,

 

 If you are anywhere near me (Aylesbury, so must be closer than Ferg!)) I'm happy to turn out and provide some hands-on help if you think that would be useful. I suffer from the delusion that I know a little about antennas (antennae?) and I have a couple of suitable SWR meters and some practical experience messing about with this sort of antenna. Please give me a call on 01296 689165 if you think that would be any use or you just want some telephone advice.

 

 Regards

 

 Bill

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=292045#292045

 

 

 

 

 

==============

 

 

 

 		 	   		     	  Quote: 	
		  [b]

jimpuglise(at)comcast.net
Guest

Posted: Sun Mar 28, 2010 5:22 am Post subject: Antenna tuning

David- 

  

I think you have been trimming your copper tape in millimeters.  I did a couple of calculations this morning and you change resonant frequency is about .38 inches (around 10 mm) per mhz.  So--if you have been trimming your foil at 2 mm per check, you would need to trim it 5 times to move it 1 mhz.  If you do your graph, you should be able to calculate very closely how you need to trim it and do it with a single cut.  

  

Jim Puglise A-283 

  

---

dpark748(at)hotmail.co.uk
Guest

Posted: Sun Mar 28, 2010 3:42 pm Post subject: Antenna tuning

Bill, Jim,

 Out of interest what kind of length did you both end up with??

 Dave

 

  Date: Sun, 28 Mar 2010 13:18:44 +0000

From: jimpuglise(at)comcast.net

To: europa-list(at)matronics.com

Subject: Re: Re: Antenna tuning



  .ExternalClass p {;}    

David-

  

 I think you have been trimming your copper tape in millimeters.  I did a couple of calculations this morning and you change resonant frequency is about .38 inches (around 10 mm) per mhz.  So--if you have been trimming your foil at 2 mm per check, you would need to trim it 5 times to move it 1 mhz.  If you do your graph, you should be able to calculate very closely how you need to trim it and do it with a single cut. 

  

 Jim Puglise A-283

  

 ---

jimpuglise(at)comcast.net
Guest

Posted: Sun Mar 28, 2010 5:10 pm Post subject: Antenna tuning

Dave- 

  

Sorry, I can't tell you.  It calculates to 43 inches, but I canabalized the included antenna and cut it for the amateur 2 meter band.  It is installed just aft of the "D" panel and cut for 146 MHZ.  I used a commercial (AAE) antenna for my comm.  It gets a touch technical, but the AAE antenna is what is called a folded dipole, so it is about twice the bandwidth of a conventional dipole.  If you attempt to trim it, it will destroy it, so you just put it in and away you go.  I am at 1/1 in the center of the band and about 1.3 / 1 at the edges with it.  If you want to spend the money, the AAE antenna is a great choice.  I also used one of theirs for my transponder.  It is a flat tape, about 1.5 inches wide and glues to the stern post beautifully.  It has a built in balun, so all you do is attach your coaxial cable and glue it in.  No tuning or trimming.     

  

Jim  



---

Bill & Sue

Joined: 10 Jan 2006
Posts: 48
Location: Malvern, Worcs. UK (Defford, Croft Farm)

Posted: Mon Mar 29, 2010 4:24 am Post subject: Re: Antenna tuning

Dave,



I'm afraid I can't help much with the length either as I haven't put the antenna in our our Europa yet ( I should be filling right now!) and anyway I ignored the Europa design (not that there is anything wrong with it) and made an aerial of my own design for fun -it came out well, but won't help in sizing your antenna.

I agree with Jim, the length quoted sounds a bit short- I would have expected about 55cm per leg, less a bit for the dielectric effects of mounting it on fibreglass. So maybe the final length in the book is about right, but I would be inclined to start a bit longer and cut to size. 

The suggestion of drawing a graph is a good one to allow you to visualise  where you are starting from.



One piece of reassurance- you can mess with the length all you like and it is very hard indeed to damage anything (a bit like fibreglass you can stick another bit on and have second crack at cutting it to size!) and, although it is nice to get it just so, small errors in the end result are likely to be unnoticeable in practice.



PS Hi Jim, we met in NZ but I didn't realise you were a Ham too- small world!

Fergus Kyle

Joined: 03 Jun 2007
Posts: 291
Location: Burlington ON Canada

Posted: Mon Mar 29, 2010 12:01 pm Post subject: Antenna Tuning

Cheers,  

        I might mention something while tuning an antenna which might make some difference. Normally an antenna up and clear  will reflect the qualities desired. But at our freqs, it’s important to ensure that nothing resembling a nearby freq exists within about a ½ to 5/8 wavelength ( a bit less) – say 300/127 m or something less than 1.5m. All this depends on orientation etc, so if a UHF or higher ferq is off the end of your tailplane dipole, not much loss of a spherical power plot. BUT if you insert a ¼-wave vertical in the plane of the diploe within a meter or so, expect the pattern of the latter’s power plot to be skewed and it won’t radiate spherically – that is pieces of the pattern will be missing power (maybe straight ahead and you have to turn the a/c 30 degrees to get the tower ahead to pay attention). High is assumed but clear is also needed.  

Nuff sed.  

ferg     [quote][b]

frans(at)privatepilots.nl
Guest

Posted: Mon Mar 29, 2010 1:45 pm Post subject: Antenna tuning

On 03/26/2010 10:43 PM, david park wrote:

 	  Quote: 	
		   I have just borrowed an SWR meter and am trying to tune my Comm

 antenna.  The manual says to tune by shortening until minimum reading at

 127.50


	


Well, somewhat contrary to what others tell you, I wouldn't make a big

deal out of it. You just need to verify that the SWR is no higher than

2.5 anywhere in the frequency spectrum you intent to use. No need to

make a graph in my opinion, just dial through the band, transmit on

every 100kHz to verify that the SWR is acceptable.



HAM's usually strive to perfection, but you aren't going to moon-bounce,

DX, trying to reach the other end of the world with 1 milliwatt, or

working with satellites.

You have 10 Watts or so to spoil, have a very short cable in comparison

to HAM-stations, are transmitting from a height HAM's usually can only

dream upon, and without obstacles in your transmission path.

You won't notice any SWR improvement from 1:2.5 to 1:1, even with a

lossy cable. Just relax.



BTW, I'm a HAM myself.



The real challenge in airplanes is to keep the interference between

avionics and your signal as minimal as possible, so spend your time on

that, rather than chasing the perfect SWR.



Just my 2 cents.



Frans

Fergus Kyle

Joined: 03 Jun 2007
Posts: 291
Location: Burlington ON Canada

Posted: Tue Mar 30, 2010 4:55 pm Post subject: Antenna Tuning

Sorry, the formula didn’t erase – please ignore 300/127m  

Tnx  

Ferg     [quote][b]

graeme bird

Joined: 15 Jul 2010
Posts: 434

Posted: Sun Mar 06, 2011 2:01 pm Post subject: Re: Antenna tuning - toriods

Interesting and relevant stuff to me - but, the ferrite's in the manual from Phillips are now obsolete, does anyone know what can be used instead. Are they critical for matching the dipole to the 50ohm cable transceiver as a balun or is it just ballast/supression at the cable end?



Thanks Graeme

_________________
Graeme Bird
kit4 (Wagstaff) TBD
Kit3 G-CLXU (Gregory) mono 914 xs Woodcomp
Kit2 G-PATS - (kesterton) Mono Classic 912 warpdrive
Kit 1 G-UMPY - Mono Classic/XS 912S, Woodcomp G(@)gdbmk.co.uk

grahamsingleton(at)btinte
Guest

Posted: Sun Mar 06, 2011 2:36 pm Post subject: Antenna tuning

Ferg Kyle might know?

Graham

From: graeme bird <graeme(at)gdbmk.co.uk>

To: europa-list(at)matronics.com

Sent: Sunday, 6 March, 2011 22:01:09

Subject: Re: Antenna tuning

--> Europa-List message posted by: "graeme bird" <graeme(at)gdbmk.co.uk (graeme(at)gdbmk.co.uk)>

Interesting and relevant stuff to me - but, the ferrite's  in the manual from Phillips are now obsolete, does anyone know what can be used instead. Are they critical for matching the dipole to the 50ohm cable transceiver as a balun or is it just ballast/supression at the cable end?

Thanks Graeme

--------

Graeme Bird

G-UMPY

Mono Classic/XS FWFD 912ULS/Warp drive FP

Build nearing completion

Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=332935#332935

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jrgowing(at)bigpond.net.a
Guest

Posted: Sun Mar 06, 2011 3:15 pm Post subject: Antenna tuning

Graham

 

I hope the ferrites are not obsolete!

I build mine in about 7 years ago and havenâ€™t used the antenna yet!

Maybe they just have something smaller or easier to use?

 

JR (Bob) Gowing UK Kit 327 in Oz

 

Do not archive

 

From: owner-europa-list-server(at)matronics.com [mailto:owner-europa-list-server(at)matronics.com] On Behalf Of GRAHAM SINGLETON

Sent: Monday, 7 March 2011 9:30 AM

To: europa-list(at)matronics.com

Subject: Re: Re: Antenna tuning

 

Ferg Kyle might know?

Graham



 



From: graeme bird <graeme(at)gdbmk.co.uk>

To: europa-list(at)matronics.com

Sent: Sunday, 6 March, 2011 22:01:09

Subject: Re: Antenna tuning



--> Europa-List message posted by: "graeme bird" <graeme(at)gdbmk.co.uk (graeme(at)gdbmk.co.uk)>



Interesting and relevant stuff to me - but, the ferrite's in the manual from Phillips are now obsolete, does anyone know what can be used instead. Are they critical for matching the dipole to the 50ohm cable transceiver as a balun or is it just ballast/supression at the cable end?



Thanks Graeme



--------

Graeme Bird

G-UMPY

Mono Classic/XS FWFD 912ULS/Warp drive FP

Build nearing completion





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=332935#332935



Navigator?Europa-List" target="_blank">http://www.matronics.com/Navigatorsp;             - MATRONICS WEB FORUMS -

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  [quote][b]

g-iani(at)ntlworld.com
Guest

Posted: Mon Mar 07, 2011 5:39 am Post subject: Antenna tuning

Graeme



I am not a radio expert but from what I have been told the ferrite rings are

needed for impedance matching (ie they are the balum).

Ian Rickard G-IANI XS Trigear, 300hours

Europa Club Mods Specialist

e-mail g-iani(at)ntlworld.com

frans(at)privatepilots.nl
Guest

Posted: Tue Mar 08, 2011 12:42 am Post subject: Antenna tuning

On 03/07/2011 02:34 PM, G-IANI wrote:



 	  Quote: 	
		   I am not a radio expert but from what I have been told the ferrite rings are

 needed for impedance matching (ie they are the balum).


	


The ferrite rings are not for impedance matching but to convert the

asymmetric signal (one center wire against an outer sleeve) in a

symmetrical one (the two legs of the dipole antenna).

Without such a conversion, the electrons can not really see the

difference between the sleeve of the coax cable and the leg of the

dipole antenna. They get confused, turn the wrong way, and radiate off

the cable instead of radiating from the dipole leg.



In this situation, it is more difficult to obtain a good and stable SWR.

Furthermore, as the sleeve of the coax cable starts radiating, you

induce more interferences in the avionics while transmitting, and

receive more noise from within the ship while receiving.



Ferrite rings are a way to "filter" the electrons. Slow moving electrons

can pass, but electrons in the mood for radiating can not, and can only

stay within the antenna. Be warned though that ferrite rings come in all

kind of flavours, if you pick a random ring from a catalog you will most

likely get one that is not efficient on the VHF frequencies we are using.



There are other ways to obtain the same result. You can coil up the coax

immediately behind the antenna connection, or create a so called

"balun". (Google on "balun" and "dipole" to find the formula how to

create such a contraption).



I have ferrite rings near the antenna connection, AND a coil in the tail

of the ship. I believe that this double measures are needed because it

is impossible to route the coax cable sufficiently far away in a 90

degree angle from the antenna, so it picks up some of the radiation from

the antenna again on the other end of the ferrite rings. The coil

further upstream takes care of this, making sure the cable is completely

"dead" between the radio and the tail of the ship.



As a result, I never have had any interference problems between the

transceiver and the rest of the avionics. Even the three strobes, fed

from a central power supply, have no influence at all at reception.



Frans

graeme bird

Joined: 15 Jul 2010
Posts: 434

Posted: Tue Mar 08, 2011 10:00 am Post subject: Re: Antenna tuning

Thanks for that, I guessed that was the case, I selected toroids that are effective in the 130Mhz range.

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