Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Is a long wire worth that effort?  (Read 1221 times)
WA9CFK
Member

Posts: 174




Ignore
« on: November 27, 2017, 09:35:51 PM »


My 160 m antenna is 130 ft long. It goes up 50 ft. then slopes down to 30 ft. on the far end.

I can add  another  300 ft. making a cantilevered antenna a bit over 400 ft long probably 20 ft or so high at the mid point.

All these height dimensions are a fraction of a wavelength at 630 m but a 400 ft wire should require a smaller loading coil than my 160 m antenna.

The question is, is it worth the effort? Usually longer is better but this low to the ground maybe not.

I hope to resonate it as a 3/4 wave on 160 m. also.


Logged
K0OD
Member

Posts: 2983




Ignore
« Reply #1 on: November 28, 2017, 07:10:20 AM »

Worth the effort for what, transmitting or receiving?  What you have will certainly let you listen unless you're in a high noise area. Transmitting is much more challenging.

For reception it's easy to learn rather precisely using WSPR how well your antenna works. Install the free WSJT-X software  and compare what you print on 630 or 2200 WSPR with what nearby stations can print. You can see exact signal reports in the WSPRnet database. You don't have to transmit to use WSPR.  http://wsprnet.org/drupal/wsprnet/map

Download WSPR software here. https://physics.princeton.edu/pulsar/k1jt/wspr.html
Logged
AA2UK
Member

Posts: 363




Ignore
« Reply #2 on: November 28, 2017, 10:21:51 AM »

If you're trying to improve RX you might try a 10' Vertical as far away from noise sources (like your home).
It appears many use short verticals or loops to improve RX. My observation is signals levels are strong enough to be copied if man and natural noise sources are managed.
Bill, AA2UK
Logged
K0OD
Member

Posts: 2983




Ignore
« Reply #3 on: November 28, 2017, 09:32:18 PM »

Some of those "short verticals" are probably e-probes mounted atop lengths of PVC tubing.

Sunday on WSPRnet a station in a rural area about 200 miles from me was copying more than just about anyone in the midwest. I'm pretty sure his antenna was a simple e-probe. I hear okay right now but I'm thinking of trying an e-probe out about 50' from the house.   
Logged
AA2UK
Member

Posts: 363




Ignore
« Reply #4 on: November 29, 2017, 07:13:13 AM »

Some of those "short verticals" are probably e-probes mounted atop lengths of PVC tubing.

Sunday on WSPRnet a station in a rural area about 200 miles from me was copying more than just about anyone in the midwest. I'm pretty sure his antenna was a simple e-probe. I hear okay right now but I'm thinking of trying an e-probe out about 50' from the house.   
A ham radio buddy of mine recently got on 630. He was reporting not hearing as well as his TX reports from others. I suggested he try a short non-res Vertical away from his house. He was using a 160 inverted V for or his resonant inverted L  on 630 RX. He reports things have gotten considerably better since he took my suggestion. He can A/B/C switch between the 160 inverted V, Inverted L and his new homebrew short non res vertical. In almost all cases the Non Resonant Vertical outperforms the 160 antenna and inverted L.
Bill, AA2UK
Logged
WA9CFK
Member

Posts: 174




Ignore
« Reply #5 on: November 29, 2017, 10:53:28 AM »

While I certainly do not question the mysteries of the RF universe, why a short vertical would work better than a tuned L or V has always perplexed me. Even on 160 m small receiving loops can work better at times.

My guess it the low impedance and other losses needed for a tuned antenna, out way the inefficiency of the high impedance short whip, straight to the receiver connection. Again it is only a guess.

A simple explanation would be helpful, also how long is a short vertical?       
Logged
AA2UK
Member

Posts: 363




Ignore
« Reply #6 on: November 29, 2017, 11:18:14 AM »

I have a couple of ideas the 1st being most 630 meter TX antennas are verticals. Then I ask myself OK why isn't this the best RX antenna? It might be that you get yourself away from close in noise sources with small Verticals where the typical TX vertical has a capacitive top hat these can be large and cover most of your property putting them close to the local noise source. I believe minimizing noise can result in better SN or SINR with digital programs. I suspect a long antenna might be more prone to picking up more noise local and atmospheric noise.
I do know most of the 630 stations that do well use separate RX non-resonant Verticals. There are also some loop antenna designs that do well these are also small and non-resonant they might be aided by their figure 8 patterns where the pattern nulls noise.
Bill, AA2UK
Logged
HAMFESTS
Member

Posts: 65




Ignore
« Reply #7 on: November 29, 2017, 11:28:44 AM »

It was explained to me this way as I had the same question some time ago.

Think of wavelength first. If the minimum for an antenna to work well is being a 1/2 wave off the ground, ten feet for a 6 meter antenna is ok.

For longwave, if the antenna is 30 feet off the ground (dipole etc..), at that wave length it's almost the same as laying the antenna on the ground.

Using a vertical you have a better chance. I found a really great PDF on the web regarding VLF antennas. Most of the best were verticals with a flat top (like a T antenna). A coil at the ground level, 50 feet of vertical antenna (wire) connected to 40 feet (I think) in the middle of a 3 wire flat top antenna. Sorry I can't describe it better. The top hat acts like a capacitor to ground. A vertical has less inter-action with surrounding objects and grounds. A 50ft vertical is a short vertical (please, anyone else can correct me)

http://electriciantraining.tpub.com/14189/img/14189_146_1.jpg

I hope that helps.
« Last Edit: November 29, 2017, 11:31:03 AM by HAMFESTS » Logged
AA2UK
Member

Posts: 363




Ignore
« Reply #8 on: November 29, 2017, 01:59:38 PM »

It was explained to me this way as I had the same question some time ago.

Think of wavelength first. If the minimum for an antenna to work well is being a 1/2 wave off the ground, ten feet for a 6 meter antenna is ok.

For longwave, if the antenna is 30 feet off the ground (dipole etc..), at that wave length it's almost the same as laying the antenna on the ground.

Using a vertical you have a better chance. I found a really great PDF on the web regarding VLF antennas. Most of the best were verticals with a flat top (like a T antenna). A coil at the ground level, 50 feet of vertical antenna (wire) connected to 40 feet (I think) in the middle of a 3 wire flat top antenna. Sorry I can't describe it better. The top hat acts like a capacitor to ground. A vertical has less inter-action with surrounding objects and grounds. A 50ft vertical is a short vertical (please, anyone else can correct me)

http://electriciantraining.tpub.com/14189/img/14189_146_1.jpg

I hope that helps.
[/quote

]That's a great LF/MF transmitting antenna called a Marconi T, it can be used for Rx.
The top wires lower the freq of the antenna's resonance (by adding capacitance).
The base coil and ground system are there for transmitter matching to the antenna assembly.
Many of the guys running these also use small non resonant Verticals for RX.
Bill, AA2UK
« Last Edit: November 29, 2017, 02:08:35 PM by AA2UK » Logged
HAMFESTS
Member

Posts: 65




Ignore
« Reply #9 on: November 29, 2017, 04:28:22 PM »

Thank you Bill for the much better explanation. That helps me too.

Here is the link for the antenna PDF I referred.

http://www.maxmcarter.com/lwantennas/index.html

click on Transmitting Antennas and Ground Systems for 1750 Meters PDF. It is a good read.

The work pioneered in the 1750 meter band by others helps us today.
Logged
WB6BYU
Member

Posts: 17171




Ignore
« Reply #10 on: November 29, 2017, 06:16:52 PM »

Quote from: WA9CFK

My 160 m antenna is 130 ft long. It goes up 50 ft. then slopes down to 30 ft. on the far end.

I can add  another  300 ft. making a cantilevered antenna a bit over 400 ft long probably 20 ft or so high at the mid point.




Top loading is certainly useful, but currents in a wire sloping downwards will be
out of phase with the current in the vertical section.  I read an analysis years ago
on a scholarly journal reporting that the top hat shouldn't extend down more than
half the height of the antenna, regardless of the length.  (Actually their number
was 55%, but I don't remember if that was up from the base or down from the
top.)

So however much wire you can install with the far end above ~25' may be
close to optimum.
Logged
WA9CFK
Member

Posts: 174




Ignore
« Reply #11 on: November 30, 2017, 09:02:40 PM »

Definitely going to have to tinker on this band.

Vertical antenna were always called noisy because of their polarity. At this frequency they seem to be the quiet options.
Logged
G8YMW
Member

Posts: 661




Ignore
« Reply #12 on: December 01, 2017, 06:27:31 AM »

I'm wondering, what about a ferrite rod aerial for receive?
Probably need some work to get some sensitivity but the ability to null a direction could be a bonus.

Thinking on a bit, MW broadcast DXers use an aerial wrapped around a frame with another wire loop (single turn) to couple the aerial to the radio.

The reason I'm thinking this is that (certainly in Blighty) not many people have room for a Topband aerial to adapt for low MF / LF
Logged

73 de Tony
Windows 10:  Making me profane since March 2017
AA2UK
Member

Posts: 363




Ignore
« Reply #13 on: December 01, 2017, 09:39:46 AM »

I'm wondering, what about a ferrite rod aerial for receive?
Probably need some work to get some sensitivity but the ability to null a direction could be a bonus.

Thinking on a bit, MW broadcast DXers use an aerial wrapped around a frame with another wire loop (single turn) to couple the aerial to the radio.

The reason I'm thinking this is that (certainly in Blighty) not many people have room for a Topband aerial to adapt for low MF / LF
Ferrite rod LF/MF antennas are in use by many stations on 630 meters. Many of these stations run 2 or more different RX antennas and switch to the one giving the S/N.
Bill, AA2UK
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!