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: Prev 1 [2] 3 4 5 6 7 ... 10 Next
 11 
 on: Today at 07:21:16 PM 
Started by KC3GQB - Last post by KC3GQB
Ill take another look at it, it the strangest thing.

 12 
 on: Today at 07:18:57 PM 
Started by K7NSW - Last post by WB5PGX
Great news about Ten Tec! If they will produce good quality American made radios at a price point that makes them a viable long term company, I am willing to pay more. Ten Tec  can become the Harley Davidson of ham radio. And for all the people that will blast me for saying this, we can just disagree and stay civil.

 13 
 on: Today at 07:00:20 PM 
Started by DL8OV - Last post by W9IQ
When using silver solder on solid state devices, take care that the soldering temperature profile is within the acceptable limits of the device.

There are two trade terms for silver solder - hard and soft. Soft silver solder is generally 3.5 to 5% silver content. Depending on the other alloys in the solder, it can take up to 450° C to melt. This is typically what is used for electronics purposes where the mating devices can tolerate the higher soldering temperatures.

The hard silver solder, up to 55% silver content, is not applied with a soldering iron but rather a torch as the temperature requirements are often double or more of soft silver solder. I have used this to join rod collinear antenna elements together for long repeater service life. It is not practical to use this for soldering solid state devices.

- Glenn W9IQ

 14 
 on: Today at 06:54:24 PM 
Started by N9LCD - Last post by WB6BYU
Certainly the first question is, "Why do you think you need a ground."  The rest of the
discussion can proceed once we understand what you are trying to accomplish.

There are multiple types of grounds, and what works well for one purpose might not
work well for others.  For starters, there are lightning grounds, AC safety grounds, and
RF ground systems for antennas fed against "ground".  There are others as well.

And there is a lot of incorrect and/or misleading information about grounding, including
on the license exams.  There isn't a simple answer.

 15 
 on: Today at 06:50:15 PM 
Started by KG6SII - Last post by N7WR
I'll weigh in here with an opinion and some will not like it.  By way of background I have been continuously licensed for 59 years.  I have been a professional in public safety (Police Chief, Fire/EMS Chief, 9-1-1 Director) for over 50 years.  I have served as an EC, DEC, SEC and Section Manager.  I was the first Chairman of the ARRL's Emergency Communications Advisory Committee and I have written 3 books on the subject of amateur radio emergency communications.  As a police chief I founded ARES/RACES groups in the cities where I served.

IMO much of what some consider AR Emergency Communications (EMCOMM) is not that at all.  It is public service communications perhaps in time of emergency and often involves H & W traffic.  While there are some examples of amateurs providing direct communications support on behalf of public safety agencies those examples are few and far between.  Amateurs may supplement the communications of public safety but they seldom if ever substitute for it (i.e. public safety comms are down and amateurs step in and provide the means by which public safety can communicate with each other).

The "Emcomm" role of AR really depends on the sophistication of the "served agencies".  With billions of dollars of DHS grants available for public safety communications equipment from 2003-2011 many agencies which might once have needed hams for communications no longer do.  They have new, robust, redundant systems and are now self reliant.  It is the schools, hospitals, Red Cross, public utilities etc that most need AR Emcomm because they did not get the huge $$$ DHS was giving away for nearly 10 years after 9/11/2001.

Those interested in serving by aligning themselves with schools, hospitals etc that will have an EMCOMM need are providing a service.  Those who simply want a badge, vest, ID, uniform by working with/for law enforcement, fire and EMS are in most (but not all) places wasting their time.  Finally while I am a life member of the ARRL and from the intro you can see I have in the past been very active with the League's EMCOMM efforts I no longer am.  I think the ARRL seized on Emcomm as a way to recruit members.  I think the League misrepresented what real world EMCOMM is all about and I think they raised some very false expectations on the part of prospective EMCOMM operators.  I think they harmed the image of amateur radio in the eyes of some public safety professionals by recruiting and assigning to public safety some ill prepared amateur radio operators who were perceived  more as "wanna be" cops and firefighters than competent communications operators.  Yes there are some examples of amateur radio operators actually doing some real Emcomm work....but much of what purports to be Emcomm is better classified as "make work".

 16 
 on: Today at 06:50:08 PM 
Started by AG7DT - Last post by W9IQ
Brian,

You gave a nice description of your installation and what you have measured then posed the question / challenge:

Quote
What's happening here? Go for it guys.  A real engineering problem.

The basic principles of what is happening are fairly straight forward. I don't mean to be condescending if you already know the following.

The external side of the coax shield is so well isolated (from an RF perspective) from the internal side of the coax shield that it can be considered a "third wire". What happens on this third wire has no meaningful impact on what is happening inside of the coax shield or the center conductor. Sometimes people have problems grasping the third wire concept because their ohm meter tells them otherwise - but this is taking a DC measurement. Because RF current only flows on the skin of any metal conductor, it typically doesn't makes it through to the other side like DC does. Each side of the shield can therefore carry a completely separate signal (frequency / phase / current / etc.). Thus the third wire.

So if you continue to think about it as a third wire, you have one end of it connected near to the feed point of the antenna and the other end is grounded just before it enters your shack. The length of this third wire, even though it is grounded, has an impedance that is allowing RF current to flow along it. This is what you observed with your RF ammeter readings. As you know, it is called Common Mode Current (CMC).

If you lengthened or shortened this third wire (and thus the entire coax) by something over a 1/8 wavelength but less than 1/2 wavelength or you removed the ground from the far end, you would likely observe a different peak current point and level of CMC and you probably would see the SWR of the antenna change. This is because the third wire is carrying some of the current from your transmitter but since it is not a feed line, it is acting as part of the antenna. And as you know, changing the length of any part of an antenna can have a real effect on SWR and other factors.

While CMC is often treated like a roach - something to be eliminated - this is not always the right answer. In the case of some antennas, CMC plays a crucial role in making it work. In these cases, the balancing act is to counteract any ill effects of CMC - such as RF in the shack, RFI in the house, pattern distortion, or noise pickup - but retain the desired role of CMC. Your grounded point just before entering the shack is probably helping to a large degree to keep the CMC out of the shack.

Many portable antennas used by portable QRP operators make good use of CMC and due to the low power and often the remote location, there are negligible bad effects from CMC so remediation is not needed.

You might find it interesting to experiment with removing the balun from your setup. A lot of things could change as a result (for better or worse). Things to check are SWR, RF in the shack, apparent antenna efficiency, noise level pickup, etc. There are enough variables that effect the outcome that a computer model would get you some approximations but field experience is the only way to be certain.

I hope that helps.

- Glenn W9IQ

 17 
 on: Today at 06:28:43 PM 
Started by VE3VEE - Last post by N7WR
Good luck everyone.  I confirmed Pitcairn on all bands many years ago when Tom Christian was alive and operating.  Years ago he was very active and it was not hard to get a QSO with that entity

 18 
 on: Today at 06:22:21 PM 
Started by KZ4USA - Last post by N7WR
I hate to be a pessimist but there is absolutely nothing to be gained by watching a video to see how an antenna works or compares with other antennas unless the R9 owner has other antennas he can quickly switch to while in the same QSO within a very short time.  You are better off reading the R 9 reviews to get an idea of what users think...and based on the reviews here on e-ham thus far I don't think I would be interested in one

 19 
 on: Today at 06:01:30 PM 
Started by WU3D - Last post by KM1H
A lot of the 7-9 pin miniature tubes didnt have the long term reliability of the octals and earlier and are more prone to leakage which reduces the bias and they run hotter and over and over.....

Ive also repaired tube type auto radios as a business for ~50 years and most original octal (except OZ4's) and big pin tubes test and work fine, vibration from prehistoric roads didnt bother them a bit.

The same for octals and 811, 803, 813, 860/861, 1625, 4CX-150, etc tubes aboard ship. Even gunnery practice didnt faze them on the WW2 era fleet oiler I spent 2 1/2 years on as an ET.

Carl

 20 
 on: Today at 06:00:56 PM 
Started by N9LCD - Last post by AA4PB
Are you looking for an RF ground because you are using an unbalanced antenna system, or just lightning protection? For lightning protection you can just ground the coax shield to a ground rod just prior to entering the house. You can't really depend on the duct work for a ground because the various pieces may not have good electrical connectivity. The cold water pipe may be okay IF it's all copper and it's properly bonded to the electrical system ground.

You might get some additional help if you can describe your antenna type, type of feed line, and how it's routed to the radio location.

Pages: Prev 1 [2] 3 4 5 6 7 ... 10 Next
Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!