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

   Home   Help Search  
Pages: Prev 1 2 [3]   Go Down
  Print  
Author Topic: 706Mk2G and Auto-Coupler in car - length of coax?  (Read 2717 times)
K0BG
Member

Posts: 9830


WWW

Ignore
« Reply #30 on: April 02, 2010, 02:44:06 PM »

Dave, that's essentially what they're doing. The problem is, the receive antenna is both near field, and very close to the ground. To get to  at least the edge of the far field, would mean the receive antenna should be about 150 feet up, to place it in the mean angle.

There is more to it, as I said before, but there are things which could be done to improve the tests. Without letting any cats out of the bag, the next shootout will be revamped in several ways. Hopefully, the readings will be closer to reality.
Logged

CHRISDX
Member

Posts: 244




Ignore
« Reply #31 on: April 04, 2010, 03:40:48 PM »

Just to be clear, I ran the 1' wire vs 10' coax test on 4 bands all within an hour, to the same station 10 miles away which had no changes.

As to why the long coax seems to have outperformed the wire, beats me. But it did.

However, I will repeat the same test. I will test 4 bands with the 1' wire feedline, then attach the oroginal comet mount's long coax and rerun the exact test to the exact station 10 miles away (a fellow ham who is working with me on this).

I'l report back on the results of the re-test.
Logged
WX7G
Member

Posts: 5908




Ignore
« Reply #32 on: April 04, 2010, 03:52:25 PM »

Chris, thanks for your fine work. Working together we can figure this all out. K0BG has the experience needed to sort this out and I'll contribute what I can.
Logged
KI4SDY
Member

Posts: 1452




Ignore
« Reply #33 on: April 06, 2010, 06:09:58 AM »

Could it be, that unshielded wire is not good for mobile installations due to all the metal in the car?
Logged
K0BG
Member

Posts: 9830


WWW

Ignore
« Reply #34 on: April 06, 2010, 06:19:00 AM »

Here's a fact. The inside of a modern vehicle is almost as RF noisy as it is under the hood! This is one of the reasons passivated glass is used. And, if RF can get out, it can get in too! This is why controlling common mode is important whenever there is an inadequate ground plane under any vertical, especially a mobile one.
Logged

WX7G
Member

Posts: 5908




Ignore
« Reply #35 on: April 06, 2010, 06:43:44 AM »

When transmitting the outside of the automobile is hot with common-mode RF current.

The automobile is one half of a vertical dipole. It is more of a vertical dipole than it is a monopole working against ground. So we are sitting inside a dipole.
Logged
WX7G
Member

Posts: 5908




Ignore
« Reply #36 on: April 07, 2010, 09:07:53 AM »

We don't have to be in the 'main beam' of the antenna to do a comparison between antenna A and antenna B. With A and B having the same elevation pattern shape we can measure at ground level.

An antenna shoot out should be a trivial measurement. We are measuring antenna systems and not particular antennas. Making claims about particular antennas based on these measurements is not correct.

About all that one can say is "my mobile system is better than your mobile system."
Logged
K0BG
Member

Posts: 9830


WWW

Ignore
« Reply #37 on: April 07, 2010, 01:23:07 PM »

Dave, I personally don't think you can even get that basic without a full-fledged test on a decent antenna range. If for no other reason than the fact ground losses are the most significant figure in determining low radiation angles. In any case, it can't be done in the near field, and that's what shootout do.
Logged

WX7G
Member

Posts: 5908




Ignore
« Reply #38 on: April 08, 2010, 02:39:41 PM »

For a mobile HF antenna the far-field can be considered to be one half wavelength. At 4 MHz this is 123 feet.

The elevation radiation pattern will be the same for two HF mobile installations.

This should be a very easy and accurate measurement. Relative measurements can be incredibly easy to do with accuracy. The variables that affect both treatments the same fall out of the error equation.
Logged
WX7G
Member

Posts: 5908




Ignore
« Reply #39 on: April 08, 2010, 05:21:04 PM »

I see from your website that you are saying that the ground in the near-field determines the radiation angle of a monopole. That is not quite correct. It is the far-field, and I mean out to 100 wavelengths, that determines the elevation pattern of a monopole mounted close to ground.
Logged
K0BG
Member

Posts: 9830


WWW

Ignore
« Reply #40 on: April 08, 2010, 06:21:12 PM »

In all due respect David, you need to do a little studying.
Logged

Pages: Prev 1 2 [3]   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!