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
Re: Topband: Radials question
The larger the diameter of the antenna, the broader the bandwidth. So an aluminum self supporting vertical that starts with 3" diameter tubing (the HD DXE starts with 4") can have twice the intrinsic bandwidth of 16ga wire. It also gets a bit shorter for same resonance frequency. I had a guyed 80m vertical of 3" irrigation tubing which had about double the bandwidth of a wire one. Another choice is a simple fixed series capacitor with a shorting relay to move the resonance up the band. I use 3 series caps and paralleled relays on my 160m T to cover all of 160 in 50KHz steps, <2:1. It worked out that the short, C, C/2, C/3 series values were right on to cover the band in even steps. The untuned resonance is 1810KHz. Others use series variable capacitors, but a vacuum variable is probably needed at the smallest value of C. That costs a lot more than fixed 1KV caps and takes longer to QSY. Grant KZ1W On 6/12/2017 20:29 PM, Mike Paskeuric wrote: Hey Topbanders, I was looking to buy or make a mono type 80 meter antenna for DXing. I was wondering couple things. If I make a full quarter wave vertical WIRE in tree 65 feet tall and see DX Engineering verticals claim 65 foot tall but wider bandwidth. What is their secret or just advertisement? Second question, I understand more radials make vertical better, but what happens if one side half or one third the length radials due to space in yard are shorter by 20 to 30 foot? Is it noticeable enough to buy a vertical in middle of yard instead of wire in tree towards side of yard? Dollars verses radial lengths. Third and last question, can some of the radials, quarter of them, overlap with radials of another antenna (160M mono vertical Gladiator antenna)? Would it affect the performance noticeable. I don't need long answers, just something to help out a bit. Not sure what antenna to buy or make yet. I am in 2 and half acres and can maybe stretch in field next to me some with no one knowing. Not many 80M momo antennas to choose from. It is a late Summer or Fall project so time to think. Mike n0 odk 73 thanks for suggestions gang. _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Radials question
Hi Mike, et al, Here are my thoughts interlaced. > Hey Topbanders, > > I was looking to buy or make a mono type 80 meter antenna for DXing. > > I was wondering couple things. If I make a full quarter wave vertical WIRE > in tree 65 feet tall and see DX Engineering verticals claim 65 foot tall > but wider bandwidth. What is their secret or just advertisement? ***Using a wire - say 12 gauge - Will probably give you a 100 kHz 2:1 SWR bandwidth. Using a vertical say 2" O.D. at the bottom and 1.25" O.D. at the top will generally triple the bandwidth. Make a model with EZNEC (r) and see what you get. Ground losses also increase band width of these antennas, since "Rg" is in series with the actual antenna impedance. > > Second question, I understand more radials make vertical better, but > what > happens if one side half or one third the length radials due to space in > yard are shorter by 20 to 30 foot? Is it noticeable enough to buy a > vertical in middle of yard instead of wire in tree towards side of yard? > Dollars verses radial lengths. ***It does not make a lot of difference. One K1 has a 160 vertical near his house and most of the radials are over 180 degrees. What is important is to get enough radials on/in the ground. > > Third and last question, can some of the radials, quarter of them, > overlap with radials of another antenna (160M mono vertical Gladiator > antenna)? Would it affect the performance noticeable. ###In my opinion, if the ground radials are below "elevated radials" for another antenna there should be no problem. The reverse is also true. I know a ham with 80 meter 4-square around a 160 meter vertical. The 80 meter radials are elevated and the 160 meter radials are in the sod. > > I don't need long answers, just something to help out a bit. > Not sure what antenna to buy or make yet. I am in 2 and half acres and can > maybe stretch in field next to me some with no one knowing. Not many 80M > momo antennas to choose from. > It is a late Summer or Fall project so time to think. > > Mike > n0 odk > 73 > thanks for suggestions gang. > _ > Topband Reflector Archives - http://www.contesting.com/_topband ***Good luck de George, K8GG _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Radials question
Mike, a different question than you asked, but if you have two trees or other supports at 65 feet or greater and more than 130ft apart, I think an 80M dipole strung between them will be a better all around antenna than a vertical. If you can get to 80ft or 100ft the dipole was be markedly better. If you only have a single support an inverted V will be almost as good. This same antenna, you can tie the feed line together at ground level and feed as a Marconi T against ground on 160M. Back to your original questions: As to differing bandwidth claims, they must be using slightly different standards for bandwidth. As long as you have more than a couple radials, I would not worry at all about an asymmetrical radial field. Put down as much copper in whatever directions you got. It's the guys with only 1 or 2 radials that have to worry about tuning. Tim N3QE > On Jun 12, 2017, at 11:29 PM, Mike Paskeuric wrote: > > Hey Topbanders, > > I was looking to buy or make a mono type 80 meter antenna for DXing. > > I was wondering couple things. If I make a full quarter wave vertical WIRE > in tree 65 feet tall and see DX Engineering verticals claim 65 foot tall > but wider bandwidth. What is their secret or just advertisement? > > Second question, I understand more radials make vertical better, but what > happens if one side half or one third the length radials due to space in > yard are shorter by 20 to 30 foot? Is it noticeable enough to buy a > vertical in middle of yard instead of wire in tree towards side of yard? > Dollars verses radial lengths. > > Third and last question, can some of the radials, quarter of them, > overlap with radials of another antenna (160M mono vertical Gladiator > antenna)? Would it affect the performance noticeable. > > I don't need long answers, just something to help out a bit. > Not sure what antenna to buy or make yet. I am in 2 and half acres and can > maybe stretch in field next to me some with no one knowing. Not many 80M > momo antennas to choose from. > It is a late Summer or Fall project so time to think. > > Mike > n0 odk > 73 > thanks for suggestions gang. > _ > Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Radials question
> was wondering couple things. If I make a full quarter wave vertical WIRE >in tree 65 feet tall and see DX Engineering verticals claim 65 foot tall >but wider bandwidth. What is their secret or just advertisement? I don't know the DX Eng. product. Usually "wider bandwidth" means flatter vswr curve at the load. There are right and wrong ways to achieve this. Right: wider driven radiator. Wrong: few radials or no radials at all. There can also be some kind of hocus pocus matching network at the feed point, and that can be okay, or a power wasting circuit depending on how it is done. I'd go with vertical wire to the tree branch and ground system and save money. It will work just as well or better if you use a lot of radials, but because it will be efficient, it will not have a flat vswr curve. You'll need a matching network in the system somewhere. If you can elevate the radials at 10 feet or higher, you may do okay with four of them equidistant and 1/4 wave long. On or below grade you need at least 60 for best performance. > Second question, I understand more radials make vertical better, but what >happens if one side half or one third the length radials due to space in >yard are shorter by 20 to 30 foot? Is it noticeable enough to buy a It probably won't be noticeable if you put down a lot of radials. > Third and last question, can some of the radials, quarter of them, >overlap with radials of another antenna (160M mono vertical Gladiator >antenna)? Would it affect the performance noticeable. It won't have any effect on performance. Do you have any metal structures near your vertical antennas? Aluminum siding, metal shedsyou should bond these with brass clamps to copper strap and run that strap back to your ground system common point. 73 Rob K5UJ _ Topband Reflector Archives - http://www.contesting.com/_topband
