Is my new nagoya antenna faulty? Please help.

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

Postby Chris P » Sat Feb 03, 2018 10:23 pm

having viewed all of your posts I would conclude that connecting your antenna to a receiver and tuning that receiver into a frequency within the designed range you may find your answer ie if you can pick up signals on it that are not heard on the standard antenna supplied with the Rx it ( the antenna) is working , it is very unlikely that this will cause any damage to the receiver as there are unlikely to be any DC voltages on the front end of the receiver circuitry as they are designed to work with antennas that have a dead short for DC such as folded dipoles . However I would not recommend that you connect your transceiver to it without getting it checked out first on an analyser . a severe mismatch could result in damage to the transmitter final stage .


In addition I conclude that the top section of the antenna is connected to the centre section via a capacitor and that the top section will pass RF signals down to the centre section at some frequencies within its designed range whilst blocking others
Regards Chris aka G8FFF nipper or tazmin88
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Re: Is my new nagoya antenna faulty? Please help.

Postby Southwales » Sun Feb 04, 2018 12:06 am

Chris P wrote:having viewed all of your posts I would conclude that connecting your antenna to a receiver and tuning that receiver into a frequency within the designed range you may find your answer ie if you can pick up signals on it that are not heard on the standard antenna supplied with the Rx it ( the antenna) is working , it is very unlikely that this will cause any damage to the receiver as there are unlikely to be any DC voltages on the front end of the receiver circuitry as they are designed to work with antennas that have a dead short for DC such as folded dipoles . However I would not recommend that you connect your transceiver to it without getting it checked out first on an analyser . a severe mismatch could result in damage to the transmitter final stage .


In addition I conclude that the top section of the antenna is connected to the centre section via a capacitor and that the top section will pass RF signals down to the centre section at some frequencies within its designed range whilst blocking others


Hi, As well as passing receive RF diwn, can it also send tx signals up to the last part, and if so would this also depend on frequency? It all sounds very clever how these loading coils work.

Not much of a test but it I tried it on FM radio on my baofeng and it picked up stations better than my original mini Nagoya mag. https://youtu.be/4XZsJgi34ZA
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Re: Is my new nagoya antenna faulty? Please help.

Postby Chris P » Sun Feb 04, 2018 9:29 am

[quote
Hi, As well as passing receive RF diwn, can it also send tx signals up to the last part, and if so would this also depend on frequency? It all sounds very clever how these loading coils work.[quote][/quote]

This is correct the top section capacitor will allow passage of RF signals to pass in both directions at some frequencies so will work on both a TX and a RX


Regarding your last test If you really want to compare two antennas you should use one receiver and a single feeder cable ( except when the antenna has an integral lead)and swap the antennas over as at uhf both the slight difference in position and the possible difference in receiver sensitivity could introduce misleading results ..


moving a VHF or UHF antenna by only a few centimetres can go from an almost full scale signal to virtually none, depending on surrounding objects including other antennas which can detune or act as directors or reflectors
Regards Chris aka G8FFF nipper or tazmin88
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Re: Is my new nagoya antenna faulty? Please help.

Postby G4RMT » Sun Feb 04, 2018 4:20 pm

First thing. You do NOT test antennas by applying 12V to them and then lighting up a lamp. It's a ridiculous way to try to work out how an antenna is wired. You use a multimeter on the resistance scale - 0-1 Ohms represents a DC short. An almost open circuit means it's not connected - but when you get readings like 500 to maybe 10 thousand Ohms, you know there's a coil I there somewhere, or some other resistive component - like in the diagrams above. The readings need interpreting.

If the little resistance is detected on the meter, then it's coils or capacitors in general - making the thing work. Sticking a bulb across 12 volts (on that big supply) means quite a few amps are available - and shorting the antenna out with a big load could easily damage it. Ohms law with 12 volts and light bulbs with umpteen watts means sensible current levels. Can the thin, weeny copper wires in the coils and other components take it?

I've got a load of antennas waiting for testing here, and one of them is similar to yours - only one coil in the whip though. I'll stick my meter on it and report back in a few minutes.

Buy even a ten quid test meter and get sensible results and no chance of damaging anything. Squirting 12Volts DC up and antenna is a risky thing to do. After all - a slip of the fingers can short out a coil with maybe 30 amps plus - quite capable of melting it! Test meters test. 12V power supplies are a different thing altogether.
EDIT
I've quickly tested the ones laying around here. The ¼ waves, as expected are a dead short from the antenna tip to the centre pin and no contact at all between the centre and the screen.

All the ones with coils show DC resistance of around 20 to 30 Ohms between the tip of the antenna and the SCREEN (outer) at the bottom. In addition there is no DC path between the centre pin and the whip.
The centre coils in a couple of the whips show around 6 to 12 Ohms resistance.

I suspect your antenna is fine.
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Re: Is my new nagoya antenna faulty? Please help.

Postby Southwales » Mon Feb 05, 2018 1:04 am

G4RMT wrote:First thing. You do NOT test antennas by applying 12V to them and then lighting up a lamp. It's a ridiculous way to try to work out how an antenna is wired. You use a multimeter on the resistance scale - 0-1 Ohms represents a DC short. An almost open circuit means it's not connected - but when you get readings like 500 to maybe 10 thousand Ohms, you know there's a coil I there somewhere, or some other resistive component - like in the diagrams above. The readings need interpreting.

If the little resistance is detected on the meter, then it's coils or capacitors in general - making the thing work. Sticking a bulb across 12 volts (on that big supply) means quite a few amps are available - and shorting the antenna out with a big load could easily damage it. Ohms law with 12 volts and light bulbs with umpteen watts means sensible current levels. Can the thin, weeny copper wires in the coils and other components take it?

I've got a load of antennas waiting for testing here, and one of them is similar to yours - only one coil in the whip though. I'll stick my meter on it and report back in a few minutes.

Buy even a ten quid test meter and get sensible results and no chance of damaging anything. Squirting 12Volts DC up and antenna is a risky thing to do. After all - a slip of the fingers can short out a coil with maybe 30 amps plus - quite capable of melting it! Test meters test. 12V power supplies are a different thing altogether.
EDIT
I've quickly tested the ones laying around here. The ¼ waves, as expected are a dead short from the antenna tip to the centre pin and no contact at all between the centre and the screen.

All the ones with coils show DC resistance of around 20 to 30 Ohms between the tip of the antenna and the SCREEN (outer) at the bottom. In addition there is no DC path between the centre pin and the whip.
The centre coils in a couple of the whips show around 6 to 12 Ohms resistance.

I suspect your antenna is fine.


Hi, thank you for your help and for going to the trouble of testing your antenna, I gave it a test today when out in my car and spoke to someone 52 miles away going by Google maps, so I would say 40 miles bee line distance.
I
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Re: Is my new nagoya antenna faulty? Please help.

Postby G4RMT » Thu Feb 08, 2018 11:43 pm

That's good news. It's quite understandable when people use common sense - after all, logic says that a bit of wire is well, a bit of wire and dead shorts shouldn't work, but RF is a mysterious thing - touching a powerful transmitting antenna - can produce no sensation at all, but move your finger along the wire a short way and you can get a proper shock, that makes you go 'ow'. Shorts that suddenly aren't shorts, and gaps between two parallel circuits can be easily crossed by RF, but not DC.

Seriously though - unlimited DC can be quite destructive if you use it to test things where a slip of the finger can burn out very thin and delicate antenna components.
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Re: Is my new nagoya antenna faulty? Please help.

Postby m0lsx » Fri Feb 09, 2018 10:36 am

G4RMT wrote: RF is a mysterious thing - touching a powerful transmitting antenna - can produce no sensation at all, but move your finger along the wire a short way and you can get a proper shock, that makes you go 'ow'.


I once saw someone loose a finger nail as he absently minded held the end of a 2 meter duck between thumb & finger & even more absently minded pressed the PTT.
Ever seen someone with the end of a duck in their mouth? It's something I tend to notice & try to discourage now.
The biggest problem with RF burns is that you normally get no sympathy. As unless it's really bad, they are under the skin & normally do not show. Back in my broadcasting days I use to tune the TX up into a light bulb by shoving one wire into the middle of the SO-239 & the other wire would just have the metal chassis of the TX laid on it. That method of tuning up earned me many an RF burn :rolleyes: :rolleyes:
A self oscillating 807 into a small oven bulb. I wonder how many amateur today would have the guts to tune a 100 watt TX into a 100 watt light bulb?
But back to voltages. With my tunable counterpoises, unless outside, I ALWAYS make sure the end of the wire is well insulated as they have been known to set fire to flooring due to the very high voltages involved at the ends of those.
Buy a database from Kimmy JS19 via http://ukscanningdirectory.co.uk/
Or do Google search of this forum via https://cse.google.com/cse/publicurl?cx=017721449704518888595:wswa65nq4ww
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Re: Is my new nagoya antenna faulty? Please help.

Postby Southwales » Sun Feb 18, 2018 1:47 pm

Not sure if this is of interest to anyone but I have now switched from the nagoya to a diamond antenna https://damsu.co.uk/mrq500-2-70cm-dual- ... tenna.html It easily outperforms the nagoya when using mobile on my uniden 125 scanner, I was in oswestury a few times this week and was getting Newtown and Telford repeaters which I had never heard from that location before and it was very clear, which is good going as on the coverage map I should be out of range. I quickly switched the nagoya back on the Magmount base and completely lost Telford and Newtown was to weak to hear, I also tried the Nagoya mini Magmount and completely lost both repeaters. I am also getting much more receive from pmr446 and the 888s baofeng out of the box frequencies. Plus more close call hits than before. Wish I had not wasted my time and money on the nagoya.

Edit, I was also in queensferry deside scanning when I picked up 430.900 with people talking, one person said he was in Ashton under Lyne very close to the repeater, does anyone know of a repeater in or close to Ashton under Lyne on 430.900 I could only find one on the frequency near Birmingham.
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