SWR Problem - UK Vintage Radio Repair and Restoration Discussion Forum

HamishBoxer · 18th Aug 2009, 12:57 pm

Not sure wether in order or not for this question.Should the height of a Windom aerial (using 1-1 balum at bottom and 4-1 at top end) effect the SWR? Should i understand be at 30 feet but more like 20 at present.This is homemade to correct spec.

Thank You David gm8jet

Skywave · 18th Aug 2009, 2:00 pm

Since a Windom uses a single-wire feeder, is a balun actually necessary?

Al. / Skywave

Station X · 18th Aug 2009, 2:53 pm

How are you feeding the antenna? If it's balanced and you're using coax then you should only need a balun at the top end, assumming your TX has an unbalanced output.

Personally I'd feed it with ladder line feeder which has a much lower loss than coax.

To answer your original question the height of an aerial above the ground does affect the impedance and hence the SWR.

In my experience people worry far too much about having a 1:1 SWR. The loss through an ATU may well be more than that due to mismatch.

HamishBoxer · 18th Aug 2009, 4:45 pm

Thank You for replies,this is a copy of a Carolina Windom which is shown to have the baluns at both ends.It is fed via coax and has a 20foot vertical coax feed between the two baluns.The swr is way above 3 or more and while i have a good atu feel it should be a lot lower prior to feeding it into this.One top wire is 30 feet and the other 80 feet aprox and should cover 80 to 10 metres.

Thanks David

Station X · 18th Aug 2009, 4:49 pm

The SWR will vary from band to band and within a band. You say you've not connected it to an ATU, as the SWR is too high. Does that mean you've tested it connected directly to a transmitter?

HamishBoxer · 18th Aug 2009, 5:27 pm

Have connected it through aerial analyser and through atu,no way would put tx straight on to it.

Station X · 18th Aug 2009, 7:10 pm

You obviously have a lot of money. The AA should tell you what the antenna looks like at various frequencies, so you'll know what balun to use and whether your ATU will be able to cope.

Peter.N. · 18th Aug 2009, 8:02 pm

I know that this is not really an answer to your immediate problem but for may years I have used a balanced dipole of about 200' , although it could be any length, fed with twin feeder into a balun directly connected to the ATU, this will usually tune 1:1 on any band, if any don't, all you have to do is adjust the length of the feeder from the transmitter end.

For portable use I have an approximate 40m dipole made from twin telephone wire, the feeder is the same wire but not split, I use a KW easymatch which has a balanced output, this also tunes up on all bands with no RF feedback problems.

Peter

HamishBoxer · 18th Aug 2009, 8:10 pm

Thank You all again.No not got a 200 foot run available.Or as much dosh as Graham thinks though!Bought analyser s/hand.

Going back to original question does anyone think height effects swr?

Regards David

HamishBoxer · 18th Aug 2009, 8:44 pm

Sorry Graham,need glasses as you gave me answer re height!

Station X · 18th Aug 2009, 8:49 pm

Quote:

Going back to original question does anyone think height effects swr?

Yes. The impedance of an aerial changes with the height above ground and this in turn will affect the SWR.

In practice all we can do is put our antennas up as high as possible and live with the result.

No one bothered much about SWR until transistorised transmitters came in which blew up if presented with anything other than a 50 ohm load. Valve transmitters are much more resilient and fitted with a PI network in the output which is effectively a built in ATU.

glowinganode · 19th Aug 2009, 12:18 am

Unhappy with the performannce of my 102' G5RV I experimented with an Off Centre Fed Dipole (Carolina Windom) by reducing one pole by 3', and adding 35' to the other. Height above ground 20'. Twin feeder approx 15' long. 4:1 balun at shack end of feeder, SWR reading less than 1.5:1 on 20M. On 80m no balun is used, the two feeders are connected to make a true Windom. SWR less than 2:1. Haven't tried the other bands, as these are the two bands I tend to work. The last 10' of each end hang down vertically as I ran out of garden.
Well please with the results, matches up better than the G5RV (in this instance with a short feeder) and brings the feed point at a more convenient position. I don't use an ATU, as I found it unnecessary with a PI tuned valve circuit, though a solid state amp might benefit if only to reduce the reflected power.
Like everything else in our hobby, it's 10% theory and 90% practice, keep experimenting until you find what works best for you.
73's, Rob.

18th Aug 2009, 12:57 pm	#1
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	SWR Problem Not sure wether in order or not for this question.Should the height of a Windom aerial (using 1-1 balum at bottom and 4-1 at top end) effect the SWR? Should i understand be at 30 feet but more like 20 at present.This is homemade to correct spec. Thank You David gm8jet

18th Aug 2009, 2:00 pm	#2
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: SWR Problem Since a Windom uses a single-wire feeder, is a balun actually necessary? Al. / Skywave

18th Aug 2009, 2:53 pm	#3
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: SWR Problem How are you feeding the antenna? If it's balanced and you're using coax then you should only need a balun at the top end, assumming your TX has an unbalanced output. Personally I'd feed it with ladder line feeder which has a much lower loss than coax. To answer your original question the height of an aerial above the ground does affect the impedance and hence the SWR. In my experience people worry far too much about having a 1:1 SWR. The loss through an ATU may well be more than that due to mismatch. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

18th Aug 2009, 4:45 pm	#4
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: SWR Problem Thank You for replies,this is a copy of a Carolina Windom which is shown to have the baluns at both ends.It is fed via coax and has a 20foot vertical coax feed between the two baluns.The swr is way above 3 or more and while i have a good atu feel it should be a lot lower prior to feeding it into this.One top wire is 30 feet and the other 80 feet aprox and should cover 80 to 10 metres. Thanks David

18th Aug 2009, 4:49 pm	#5
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: SWR Problem The SWR will vary from band to band and within a band. You say you've not connected it to an ATU, as the SWR is too high. Does that mean you've tested it connected directly to a transmitter? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

18th Aug 2009, 5:27 pm	#6
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: SWR Problem Have connected it through aerial analyser and through atu,no way would put tx straight on to it.

18th Aug 2009, 7:10 pm	#7
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: SWR Problem You obviously have a lot of money. The AA should tell you what the antenna looks like at various frequencies, so you'll know what balun to use and whether your ATU will be able to cope. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

18th Aug 2009, 8:02 pm	#8
Peter.N. Dekatron Join Date: Jul 2008 Location: Charmouth, Dorset, UK. Posts: 3,601	Re: SWR Problem I know that this is not really an answer to your immediate problem but for may years I have used a balanced dipole of about 200' , although it could be any length, fed with twin feeder into a balun directly connected to the ATU, this will usually tune 1:1 on any band, if any don't, all you have to do is adjust the length of the feeder from the transmitter end. For portable use I have an approximate 40m dipole made from twin telephone wire, the feeder is the same wire but not split, I use a KW easymatch which has a balanced output, this also tunes up on all bands with no RF feedback problems. Peter

18th Aug 2009, 8:10 pm	#9
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: SWR Problem Thank You all again.No not got a 200 foot run available.Or as much dosh as Graham thinks though!Bought analyser s/hand. Going back to original question does anyone think height effects swr? Regards David

18th Aug 2009, 8:44 pm	#10
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: SWR Problem Sorry Graham,need glasses as you gave me answer re height!

19th Aug 2009, 12:18 am	#12
glowinganode Octode Join Date: Apr 2009 Location: Aylesbury, Buckinghamshire, UK. Posts: 1,522	Re: SWR Problem Unhappy with the performannce of my 102' G5RV I experimented with an Off Centre Fed Dipole (Carolina Windom) by reducing one pole by 3', and adding 35' to the other. Height above ground 20'. Twin feeder approx 15' long. 4:1 balun at shack end of feeder, SWR reading less than 1.5:1 on 20M. On 80m no balun is used, the two feeders are connected to make a true Windom. SWR less than 2:1. Haven't tried the other bands, as these are the two bands I tend to work. The last 10' of each end hang down vertically as I ran out of garden. Well please with the results, matches up better than the G5RV (in this instance with a short feeder) and brings the feed point at a more convenient position. I don't use an ATU, as I found it unnecessary with a PI tuned valve circuit, though a solid state amp might benefit if only to reduce the reflected power. Like everything else in our hobby, it's 10% theory and 90% practice, keep experimenting until you find what works best for you. 73's, Rob. __________________ We have done so much, for so long, with so little, we are now qualified to do anything with nothing.