Is my new nagoya antenna faulty? Please help.

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Is my new nagoya antenna faulty? Please help.

Postby Southwales » Fri Feb 02, 2018 12:31 pm

Hi, just purchased a new nagoya antenna and unbranded mag mount, first off I found a short on the magmount base. Basically to test this I sent a current down the centre of the so239 on the mag mount but on the pl plug end that attaches the radio both the inner pin and outer thread got a live feed which is how I was sure I had a short.

On further inspection I found it was down to the centre coax core made contact with the assembly bolt, the manufacturer used what looks like aquarium sealant to insulate but the assembly bolt had cut through this once tightened. Luckily I tested before connecting to any of my radios, would it have damaged my radios if I had of connected or transmitted?


Just now I thought I would also test the antenna itself, I have connected a live feed at the top of the antenna but it is the outer shell that is getting the live feed, the centre pin get nothing, is this right or wrong, please see video.if it is faulty can you please comment on the video so I can inform and show the seller.

https://youtu.be/q55xcstRbbo

One of the reasons I am thinking it is faulty or is that if I do the same on any other antenna such as my Moonraker magmount it is the centre pin that lights up.

If I have got this wrong and the Nagoya is normal then my final question is that although I say I connect the live feed to the top part of the antenna it is actually the middle between the 2 loading coils, if I go to the top of the antenna no current flows at all past the upper loading coil, what is the point to the upper last section of the antenna if no current flows through? Thank you for any help and advice.
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Re: Is my new nagoya antenna faulty? Please help.

Postby Southwales » Sat Feb 03, 2018 8:52 am

Hi, Could I be correct in thinking the centre pin inside the antenna is not actually connected to anything and would damage my radio if I was to TX?. If I attach a live feed to the centre pin I can not get a live feed on any other part of the antenna leading me to believe the centre pin is not actually connected to anything.
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Re: Is my new nagoya antenna faulty? Please help.

Postby m0lsx » Sat Feb 03, 2018 9:58 am

The real issue is what is the VSWR like when connected to a decent metal surface? As you should NEVER transmit into an antenna without checking that.
Using your test to check between the coax connectors is one thing, as you do not want continuity between inner & outer on the coax. But what are you seeing in the antenna, by doing what you are doing? Different designs will show different results. So what you are doing is to a certain extent is meaningless, especially so, as you do not now understand what you are seeing.
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Re: Is my new nagoya antenna faulty? Please help.

Postby Southwales » Sat Feb 03, 2018 10:21 am

m0lsx wrote:The real issue is what is the VSWR like when connected to a decent metal surface? As you should NEVER transmit into an antenna without checking that.
Using your test to check between the coax connectors is one thing, as you do not want continuity between inner & outer on the coax. But what are you seeing in the antenna, by doing what you are doing? Different designs will show different results. So what you are doing is to a certain extent is meaningless, especially so, as you do not now understand what you are seeing.


Hi, My swr meter is on order, As I mainly use my antennas for recieving with my scanner and uv-5rv this is mainly what I am looking for in an antenna, being able to use it with my cb later on will be a bonus but something I am not to concerned about at the moment.

Are you saying it is normal for the outer thread to be the part that makes contact with the antenna length itself rather than the centre pin, because surely that is what my test prooves?.If I can not complete a connection at the centre pin to the length of the antenna itself then surely that is doing nothing or at least not connected to anything? And surely with the way a magmount base would be wired so that it is the centre coax condutor that feeds the centre pin on the antenna itself? I thought it was the centre conductor that done the main part of receiving and transmission?

Below hen I do the same test on my moonraker magmount I get a live feed to the centre pin as expected, I would not expect to get it to the outer threaded part of the plug.

Image


And here when the naygoa in question is attached which surely is wrong as I am still getting the live feed at the outside of the plug and nothing on the centre pin. Which as from the video in the first post we know stems from the naygoa itself not being attached at the centre pin but the outer threaded part.

Image
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Re: Is my new nagoya antenna faulty? Please help.

Postby m0lsx » Sat Feb 03, 2018 11:21 am

Southwales wrote: Are you saying it is normal for the outer thread to be the part that makes contact with the antenna length itself rather than the centre pin, because surely that is what my test prooves?.


What I am saying is. You have carried out a test that proves nothing to you, as you do not understand why you are getting the results that you are.
Inside a CB antenna called a Anton 99, which is a white fibreglass vertical, there is something called a Shunt. This is the bottom 2 feet of the antenna. It is two lengths of coiled wire. One forms a quarter wave. The second a loading coil. These are not connected to the shield at the bottom of the coils, but to the inner core. BUT they are connected & separately, above those coils using capacitors. And the centre core of the coax actually has no direct contact with the top radiating element, except via those very same capacitors which are themselves gaps that only allows flow in one direction.

Image

This a Bazooka antenna. The inner core & outer braid are soldered togther at a set point.
Image


This a folded dipole. It is a loop & look at how the coax is connected to it.
Image
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Re: Is my new nagoya antenna faulty? Please help.

Postby Chris P » Sat Feb 03, 2018 11:33 am

to put it simply the centre conductor is normally connected to the whip element of a vertical antenna with the outer braid connected to the ground plane element ( eg radials ). Adding traps or loading coils will effect the way a circuit appears to measuring/test equipment


I think southwales would benefit from reading " out of thin air " or another similar publication to understand the basics of receiving antennas and the way RF differs from DC. For example a capacitive connection will allow RF to flow but not DC so would appear to be an open circuit if measured with an ohmmeter and an inductive connection may appear to be a short on DC but can act as a high impedance to RF.

In addition looking at the test equipment in use a cheap ( you can get them for a few pounds on the internet ) multimeter maybe a worthwhile investment even a few amps at 12VDC can melt a thin cable and cause a burn or fire let alone a 12VDC jumpstart supply which can produce tens of amps
Regards Chris aka G8FFF nipper or tazmin88
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Re: Is my new nagoya antenna faulty? Please help.

Postby Southwales » Sat Feb 03, 2018 11:52 am

m0lsx wrote:
Southwales wrote: Are you saying it is normal for the outer thread to be the part that makes contact with the antenna length itself rather than the centre pin, because surely that is what my test prooves?.


What I am saying is. You have carried out a test that proves nothing to you, as you do not understand why you are getting the results that you are.
Inside a CB antenna called a Anton 99, which is a white fibreglass vertical, there is something called a Shunt. This is the bottom 2 feet of the antenna. It is two lengths of coiled wire. One forms a quarter wave. The second a loading coil. These are not connected to the shield at the bottom of the coils, but to the inner core. BUT they are connected & separately, above those coils using capacitors. And the centre core of the coax actually has no direct contact with the top radiating element, except via those very same capacitors which are themselves gaps that only allows flow in one direction.

Image

This a Bazooka antenna. The inner core & outer braid are soldered togther at a set point.
Image

So it this why I am also not getting a connection between the last/top small loading coil but can through the middle one see images below?, are you saying that although the current does not flow an RF signal will? Sorry if these all seem like silly questions but I am just trying to understand how my naygoa basically works as obviously it is not like any of my other antennas.

The Antrim 99 you refer to, are you saying that my naygoa will I have loading coils that work similar to this?, will the bottom of my Nagoya likely have a coil in there or will it just the the middle and top visible ones? And I guess the most important question of all, Is this antenna more than likely working as it should and I am safe to connect it to my radios?

Image


Image
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Re: Is my new nagoya antenna faulty? Please help.

Postby m0lsx » Sat Feb 03, 2018 1:46 pm

[quote="Southwales"] Are you saying that although the current does not flow an RF signal will? Sorry if these all seem like silly questions but I am just trying to understand how my naygoa basically works as obviously it is not like any of my other antennas./quote]

What I am saying is, that what you are doing is just confusing yourself. As Chris P said get yourself a good book that covers the basics & his suggestion of Practical Wireless's, Out of thin air is an excellent starting point. It was my first antenna book in about 1980, when I wanted to move beyond an end fed wire. Out of Thin air will not answer your question & nor will it's follow on book. More out of thin air. But it will show you some of the basics behind antennas.
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Re: Is my new nagoya antenna faulty? Please help.

Postby Southwales » Sat Feb 03, 2018 6:22 pm

So I understand my test have may have caused some confusion but take my question on the top loading coil, would you say that although my test shows an open circuit an RF signal will still travel between the 2 sections of antenna? And I know my tests have proved very little but would in your opinion say that my antenna is not faulty and me getting a current on the outside of the connector instead of the centre is probably correct for this type of antenna?
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Re: Is my new nagoya antenna faulty? Please help.

Postby m0lsx » Sat Feb 03, 2018 6:52 pm

The answer is we do not know if the antenna is faulty or working. Only loading the antenna either a antenna analyser, which are expensive or into a SWR meter will start to answer that one. And do not forget antennas have a specified operating frequency, you cannot just load it with RF & get an answer. Also the fact that the manufacturer claims a SWR below say 1:1.5 across a certain band does not mean it is so.
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