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Author Topic: Wouxun UV3D + Diamond NR73B = NO RX/TX  (Read 4216 times)
KC2ZPK
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« on: April 11, 2011, 06:08:06 PM »

ok, on my way up to a real mobile radio my first stop was to get an antenna for the cars so I can use my Wouxun HT and get a little better then the stock rubber ducky. So I got a Diamond  NR73B with a NMO mount. One car has a through hole NMO and the other has a trunk lip NMO mount. Either one the result is the same, as soon as I hook up the NR73B, the Wouxun goes deaf, and transmitting does nothing. Yes the transmit light comes on, but I can't even reach the local repeater, which is only a mile away. And the NOAA stations that came in crystal clear are now gone. Without the antenna mounted I do not have continuity between the center conductor and the braid, so there are no shorts, and the braid has continuity to body ground on the cars. When I screw the antenna onto the mount I now have continuity between the center and the outer braid, and no reception. IF I only connect the center conductor, and let the braid float I have decent reception, and can at least hit the local repeater so that is replies with it's callsign.

Something can't be right  Huh .....
Any ideas??

Thanks
John
KC2ZPK
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John
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K7RBW
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« Reply #1 on: April 11, 2011, 07:46:20 PM »

Are you powering the radio off the car through a battery eliminator or are you using batteries?

If your powering it off the car, try running it on just batteries so it's not getting power from the car.

Have you tried another radio (e.g. from a fellow Ham)?

Just some ideas to try to narrow things down and eliminate some possible causes.
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KC2ZPK
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« Reply #2 on: April 11, 2011, 08:10:36 PM »

Are you powering the radio off the car through a battery eliminator or are you using batteries?

If your powering it off the car, try running it on just batteries so it's not getting power from the car.

Have you tried another radio (e.g. from a fellow Ham)?

Just some ideas to try to narrow things down and eliminate some possible causes.


Been using the batteries, haven't tried another radio yet. I thought it might be a ground issue as well.
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John
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K7RBW
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« Reply #3 on: April 12, 2011, 05:39:26 AM »

That's a stumper...

The only other thing that comes to mind is perhaps there's a connector problem in the cable somewhere. For example, where the center pin is too short to make a good connection (I've seen that in BNC connectors where the center pin gets pushed in enough to lose contact but it's hard to tell visually) I've also seen that happen with some bargain adapters where they don't quite mate perfectly.

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KC7YRA
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« Reply #4 on: April 12, 2011, 06:40:07 AM »

That certainly is odd.  But not unheard of.

My first guess would be a connector not making contact.  If so, it should be an easy fix.

My 2nd guess is based upon me having the exact same problem.  I had an IC-W32A years ago and it worked ok as an HT.  But when hooked up to a mobile magmount, the radio became totally deaf.  It was as if it were not connected to an antenna.  I could not tell I was keying up a repeater, nor hear any public safety stuff.  It was completely useless in any kind of RF dense environment.  Despite really liking the HT, I sold it as it was just not acceptable to NOT hear completely usable signals.

Brad
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KC2ZPK
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« Reply #5 on: April 12, 2011, 07:47:13 AM »

That's a stumper...

The only other thing that comes to mind is perhaps there's a connector problem in the cable somewhere. For example, where the center pin is too short to make a good connection (I've seen that in BNC connectors where the center pin gets pushed in enough to lose contact but it's hard to tell visually) I've also seen that happen with some bargain adapters where they don't quite mate perfectly.

I thought the same at first, but read below.


That certainly is odd.  But not unheard of.

My first guess would be a connector not making contact.  If so, it should be an easy fix.

My 2nd guess is based upon me having the exact same problem.  I had an IC-W32A years ago and it worked ok as an HT.  But when hooked up to a mobile magmount, the radio became totally deaf.  It was as if it were not connected to an antenna.  I could not tell I was keying up a repeater, nor hear any public safety stuff.  It was completely useless in any kind of RF dense environment.  Despite really liking the HT, I sold it as it was just not acceptable to NOT hear completely usable signals.

Brad

What I tried is this...
I cut the PL-259 off the coax, and striped the coax so I had about 2" of center conductor, and about 1/2" of braid exposed. I had a spare BNC to F adapter handy and attached it to the radio, then inserted the center conductor into the F side of the adapter and the radio came to life. I could hear the local repeater and key up into it. As soon as I touch the braid to the outside of the f connector, all went silent and I could not key the repeater.

So now I moved to checking the antenna. As you can see in my first post, the coax is not shorted or open where it should not be. When I check for continuity between the center pin on the antenna and the base I DO HAVE continuity (loading coil?). I tried to measure the resistance and it is greater than my meter goes up to.

The HT does work with the stock ducky.
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John
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KC2ZPK
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« Reply #6 on: April 12, 2011, 09:38:43 AM »

One thing has come to mind.... Will the Wouxun HT work with a DC grounded antenna?
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John
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AD7C
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« Reply #7 on: April 15, 2011, 09:57:21 AM »

When I check for continuity between the center pin on the antenna and the base I DO HAVE continuity (loading coil?). I tried to measure the resistance and it is greater than my meter goes up to.

It appears you have a defective antenna or mount/coax.  Shielding shorting to ground.  An antenna with a loading coil does not bridge the center to ground.  A matching coil (for impedance) does.

Beg, Borrow, Steal (well, let's skip that one) an SWR meter or antenna analyzer.  You'll find the problem fast and save all the guess work.  A basic SWR meter for 2M/70cm is cheap and worth the investment.  I had the same HT and used lot's of different external antennas without issue.  

Rich
KE7SAK
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KC2ZPK
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« Reply #8 on: April 15, 2011, 10:08:08 AM »

When I check for continuity between the center pin on the antenna and the base I DO HAVE continuity (loading coil?). I tried to measure the resistance and it is greater than my meter goes up to.

It appears you have a defective antenna or mount/coax.  Shielding shorting to ground.  An antenna with a loading coil does not bridge the center to ground.  A matching coil (for impedance) does.

Beg, Borrow, Steal (well, let's skip that one) an SWR meter or antenna analyzer.  You'll find the problem fast and save all the guess work.  A basic SWR meter for 2M/70cm is cheap and worth the investment.  I had the same HT and used lot's of different external antennas without issue.  

Rich
KE7SAK


Without the antenna on the mount it is fine, and when I check the resistance  of the antenna's center pin to outer mounting thread, I have a very high resistance, but have continuity. I will be getting a SWR meter for VHF soon.
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John
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VA3WXM
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« Reply #9 on: April 15, 2011, 03:06:14 PM »

The NR73B appears to be 1/2 wave on 2M (and 5/8 over 5/8 for 70CM).  That means there is an impedance matching network of some kind in the antenna base because end-feeding a 1/2 wave antenna requires a high impedance.  That would explain why you have DC continuity when the antenna is on the mount.

Have you tried another antenna?  It could be that the Diamond is bad (it does happen).

Also keep in mind Comet and Diamond NMO antennas do not mate well with Motorola/Larsen/etc. NMO mounts.  The thread pitch is slightly different.
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KC2ZPK
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« Reply #10 on: April 16, 2011, 03:43:00 PM »

The NR73B appears to be 1/2 wave on 2M (and 5/8 over 5/8 for 70CM).  That means there is an impedance matching network of some kind in the antenna base because end-feeding a 1/2 wave antenna requires a high impedance.  That would explain why you have DC continuity when the antenna is on the mount.

Have you tried another antenna?  It could be that the Diamond is bad (it does happen).

Also keep in mind Comet and Diamond NMO antennas do not mate well with Motorola/Larsen/etc. NMO mounts.  The thread pitch is slightly different.

OK....

I spoke to a tech at Diamond, and we went over a few things. The antenna is DC coupled, and I should have no continuity between the center pin of the antenna to the threads. I should have continuity from the antenna base thread to the lower antenna section. I will reconfirm this with him on Monday, as I have a few questions now.

OK what I did...

I put a new PL-259 on, and made sure there were no opens or shorts in the cable out to the trunk lip mount. I screwed the antenna on just enough to start the threads and and checked for continuity at the PL-259. I kept checking as I screwed the antenna down. No continuity until the very last 1/2 turn, then Wham! continuity!!  From what I can tell, the base of the antenna is shallower then the base of the NMO mount. so as you screw down the antenna the pin on the antenna is pushed all the way in and the brass center contact of the NMO mount makes contact with the pin and the bottom side of the antenna base causing a short. I grabbed the gasket from a NMO weather cap and put that between the mount and the antenna. That 1/16"-3/32" made all the difference. The radio is no longer deaf, and even the NOAA channels come in clear. I thought it should have had a gasket anyway. Smiley

As far as the thread difference?? On the trunk lip mount I didn't notice, but on Larson through hole, I did notice some roughness, but still went on. What are the Diamond antenna supposed to mount with?

Thanks
John
KC2ZPK

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John
KC2ZPK.com - A work in progress
VA3WXM
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« Reply #11 on: April 17, 2011, 02:07:54 PM »

Diamond "NMO" mounts are meant for Diamond antennas.
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WV4I
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« Reply #12 on: April 24, 2011, 06:11:12 AM »

The UV3D has a male SMA antenna chassis connector. Most/all other HTs that I know of have a female SMA chassis mount. So your antenna cable, radio end, must have a female connector (uncommon) or you need to use a SMA type fem-fem coupler.

Also, look carefully at all SMA center pins on the male side, for damage.

Do you have continuity on center pin of cable from end to end?
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KJ4GZI
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« Reply #13 on: May 12, 2012, 03:25:22 PM »

Also keep in mind Comet and Diamond NMO antennas do not mate well with Motorola/Larsen/etc. NMO mounts.  The thread pitch is slightly different.
OK what I did...

I put a new PL-259 on, and made sure there were no opens or shorts in the cable out to the trunk lip mount. I screwed the antenna on just enough to start the threads and and checked for continuity at the PL-259. I kept checking as I screwed the antenna down. No continuity until the very last 1/2 turn, then Wham! continuity!!  From what I can tell, the base of the antenna is shallower then the base of the NMO mount. so as you screw down the antenna the pin on the antenna is pushed all the way in and the brass center contact of the NMO mount makes contact with the pin and the bottom side of the antenna base causing a short. I grabbed the gasket from a NMO weather cap and put that between the mount and the antenna. That 1/16"-3/32" made all the difference. The radio is no longer deaf, and even the NOAA channels come in clear. I thought it should have had a gasket anyway. Smiley

As far as the thread difference?? On the trunk lip mount I didn't notice, but on Larson through hole, I did notice some roughness, but still went on. What are the Diamond antenna supposed to mount with?

Thanks
John
KC2ZPK

Well I just installed a Kenwood 281 in my truck and experienced the same problem with the radio being deaf with the power on though I could hear WX channel.  Took my new radio back to the store (AES) where I purchased it from, and they verified that the radio was working.  Therefore this left only the mount (Larsen NMO) or antenna (Diamond NR73BNMO) being bad. I Ohm's check the cable it seem Ok but was shorted with the antenna installed, I was not sure if this correct or not. 

I was searching for threads on troubleshooting my antenna when I came across this thread went out to my truck and turned the antenna a little bit and turned on my radio and it was functioning like it should.  Thanks to John for finding the problem and posting his results otherwise I am not sure I would have ever figured out the problem.  I will be sure to let the store know what the issue was so they can let future customer know beforehand.

George
 
« Last Edit: May 12, 2012, 03:26:55 PM by KJ4GZI » Logged
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