Re: Topband: Short Verticals
As I understand it, if you reduce the effect of ground loss by using raised radials you should get a more predictable and consistent result. So, your main radiator, the vertical, sits between 2 sets of radials, one set at the top and one at the bottom. My feeling is that this gets the most efficient result. Most software doesn't like radials close to or in the ground, so I would do the modeling then make one to do real measurements. From there you can plug in accurate figures for your phasing system. I came across this, which you probably know all about: http://www.kkn.net/dayton2005/ON4UN-Dayton-2005.pdf Will you be using wires, poles or towers? Wish I had the space. David G3UNA - Original Message - From: "David Cole via Topband" To: Sent: Tuesday, June 13, 2017 10:08 PM Subject: Topband: Short Verticals Hi all - Assuming a standard 1/4 wave vertical is 36 ohms - is there any formula that will calculate the Z if the vertical is short and brought to resonance by top loading wires - I understand the Z will be less - but how much by ? I am trying to use the formula on ON4UN disc to calculate the approx LC ratios for a Lahlum-Lewallen phasing system. Thanks Dave g3rcq _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Short Verticals
Hi Dave, There is a very accurate formula to calculate radiation resistance of vertical radiators that are 1/8 wavelength or shorter in physical length that's in the ARRL Antenna Book, and this formula provides values very close to those you would obtain using 4nec2 (you could use this formula to compare the radiation resistance of a short vertical to your 36 ohm radiation resistance value for a 1/4 wavelength over perfect ground to determine the approximate difference in feedpoint impedance (assuming similar ground losses in both cases). Unfortunately the use of top loading wires complicates the issue as the radiation resistance will also be dependent on the length of the top loading wires, the number of top loading wires, and the angle of the top loading wires. I suspect there is already published data regarding the radiation resistance for various top loading cases. As Clive mentioned, EZNEC or 4nec2 is the best way to estimate the radiation resistance of the shorter top loaded vertical. 73, Don (wd8dsb) On Tue, Jun 13, 2017 at 5:08 PM, David Cole via Topband < topband@contesting.com> wrote: > Hi all - > Assuming a standard 1/4 wave vertical is 36 ohms - is there any formula > that will calculate the Z if the vertical is short and brought to resonance > by top loading wires - I understand the Z will be less - but how much by ? > I am trying to use the formula on ON4UN disc to calculate the approx LC > ratios for a Lahlum-Lewallen phasing system. > Thanks Dave g3rcq > _ > Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Short Verticals
Eznec is your friend Dave. Having used a previously short Vertical 51ft for 20+ years, the top loading is not your problem. Because the feed Z is low you will require longer radials. Mine are typically 0.4 wavelengths. I will stand corrected but the formula is E (efficiency) = Feed Z/ Feed Z plus loss (the loss being mainly ground loss) So typically with a short vertical we could have 12/ 12+ plus loss which could be any amount dependent on your radial system. The only way to deal with this is either by a vast radial system or a taller vertical. In the end it's all a numbers game. 73 Clive GM3POI (306 current confirmed) -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of David Cole via Topband Sent: 13 June 2017 21:08 To: topband@contesting.com Subject: Topband: Short Verticals Hi all - Assuming a standard 1/4 wave vertical is 36 ohms - is there any formula that will calculate the Z if the vertical is short and brought to resonance by top loading wires - I understand the Z will be less - but how much by ? I am trying to use the formula on ON4UN disc to calculate the approx LC ratios for a Lahlum-Lewallen phasing system. Thanks Dave g3rcq _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Short Verticals
Hi all - Assuming a standard 1/4 wave vertical is 36 ohms - is there any formula that will calculate the Z if the vertical is short and brought to resonance by top loading wires - I understand the Z will be less - but how much by ? I am trying to use the formula on ON4UN disc to calculate the approx LC ratios for a Lahlum-Lewallen phasing system. Thanks Dave g3rcq _ Topband Reflector Archives - http://www.contesting.com/_topband
