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Antenna SWR on land

 
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Ken O



Joined: 05 Mar 2014
Posts: 32
City/Region: Billings
State or Province: MT
PostPosted: Sun Nov 08, 2020 10:49 pm    Post subject: Antenna SWR on land Reply with quote

I just installed a new antenna on my new (used) boat:

https://www.westmarine.com/buy/shakespeare--5104-4-classic-vhf-marine-band-antenna--12008215

The radio, an older Cobra MR F55 pulls in the local weather service channel very well, but the SWR is about 6.0 (not good). Shakespeare says this antenna should come in around 1.5 for SWR. I am more familiar with SWR on vehicles, where the body acts as a ground plane, and I know water can act somewhat as a ground plane. Would the SWR on a fiberglass C-Dory get better on the water instead of on a trailer?

What am I missing? The connector was a solder-on type, which I know can fail if not soldered well. The radio is untested. What should I try next? I'd like to fix this before I get on the water and really need to transmit. Thanks.
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jkidd



Joined: 23 Oct 2006
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PostPosted: Sun Nov 08, 2020 11:03 pm    Post subject: Reply with quote

Find someone who has an antenna analyzer and have them test it. One of your local hams should have one.

Also that antenna doesn’t need a ground plane.

How are you getting your swr’s with a meter for marine band not one for cb.

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hardee



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PostPosted: Mon Nov 09, 2020 12:11 am    Post subject: Reply with quote

Be sure when you are doing your testing that you are not inside a building, and that you have some space between your antenna and neighboring building or structure.

Harvey
SleepyC Moon


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Ken O



Joined: 05 Mar 2014
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City/Region: Billings
State or Province: MT
PostPosted: Mon Nov 09, 2020 7:54 am    Post subject: Reply with quote

The antenna is within 10 feet of my garage, which could be an issue. The SWR meter I am using is for ham radio VHF, which is in the 140's mHz range, so it should be close enough. I'm going to try re-doing the connector also. Thanks for the ideas.
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thataway



Joined: 02 Nov 2003
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PostPosted: Mon Nov 09, 2020 2:50 pm    Post subject: Reply with quote

The 2 meter frequency is close enough. The garage being 10 feet away, may be an issue, if it is a metal structure. Probably not if normal stick and frame construction.

If I buy antennas from West Marine, I take my MFJ antenna analyzer with me. I have found a number of Shakespeare antennas which had high SWR.

Morad makes an excellent antenna. They are SWR checked at the factory. They are a bit more expensive, but very robust. Often used in LEO, & Commercial vessels. The "hot rod" for 156 Mhz is very close to the 156.8 frequency of channel 16. They make other frequency resonate antennas for AIS, Ham, Specific Commercial or LEO use. You need to use their mounts, their cable and fittings, not cut the cable in this case. (OK for most antennas)

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Bob Austin
Thataway
Thataway (Ex Seaweed) 2007 25 C Dory May 2018
Thisaway 2006 22' CDory November 2011 to May 2018
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Thataway TomCat 255 150 Suzukis June 2006 thru August 2011
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Home port: Pensacola FL
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Ken O



Joined: 05 Mar 2014
Posts: 32
City/Region: Billings
State or Province: MT
PostPosted: Mon Nov 09, 2020 5:29 pm    Post subject: Reply with quote

Thanks Bob. The garage is stick-built, so probably not an issue. I think I'm going to re-do or replace the connector. Shakespeare says this antenna should come in around 1.5 SWR, but, as you say, there's probably less quality control. I'm thinking I'm kind of stuck with this one, or in for a long argument with West Marine or Shakespeare.
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thataway



Joined: 02 Nov 2003
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PostPosted: Mon Nov 09, 2020 8:09 pm    Post subject: Reply with quote

How is the PL 259 fitting fitted to the cable? I am not a fan of the "crimp" on type of fittings. I am old fashioned, and solder them. I did a tutorial on this in the past. The photos in my album #320 to #332 on page 10 of the "Thataway"
album

From the past: Incidentally the crimp on PL 259 plugs are no where as good as a properly soldered plug. I have seen this demonistrated may times. Unfortunately many people do not know how to properly solder the PL 259 plug.
Here are a couple of articles on proper technique:
http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/SolderCoax.htm
http://www.hcarc.us/articles/soldering%20PL-259%20connectors.htm

There are several pitfalls. One is that you have to solder the braid to the connector, thru the holes in the body. Second, if you get the connector too hot, you can distort the phenolic insulator, which holds the center connector.
I use Vise Grips or a machinists vise, as heat sinks, and I small torch. If you use a soldering iron, a 100/150 watt iron is marginal; Far better is the 200/260 watt gun. (you can get cloth cutting tips for these irons, for sealing acrylic fabrics). I'll admit I have more than the average number of soldering irons....
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garyf



Joined: 01 Sep 2015
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PostPosted: Mon Nov 09, 2020 11:25 pm    Post subject: Reply with quote

100% agree with solder over crimp with coaxial connectors with the caveat that soldering can be done wrong too (very wrong).

And, actually, crimps can be pretty reliable if you get the high $$ connectors and the VERY high $$$$ crimpers - but most mortals will not spend the money.

I did connectors for nuclear instrumentation on reactors. They were required to be soldered by (and to) spec.

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thataway



Joined: 02 Nov 2003
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PostPosted: Tue Nov 10, 2020 12:04 pm    Post subject: Reply with quote

Gary makes good points. There are the professional crimped PL 259, but are large and not easy to thread thru many openings or tubing runs.

There is the soldered, and Shakespeare makes a connector where the braid is basically held between the body of the PL 259 and the adaptor for the cable size.

The Pinch type of connection where you cut the cable flush, and slip the fitting on hoping to pierce the exact center of the cable core conductor, and then 4 prongs pierce the outer vinyl insulation and give some ground connections to the shield of the cable.



Finally the FME or similar small connection which is placed on the cable by the manufacture (such as Morad) and then an adaptor from FME to PL 259 is screwed on after the cable has. been run. The FME connector is able to go thru most tubes and a 5/16" to 3/8" hole.



There is an adaptor which screws onto FME adaptor, to PL 259:



Digital Marine VHF antennas, can also. be had with a mini UHF connector, of small size with a PL 259 adapter.
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Ken O



Joined: 05 Mar 2014
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City/Region: Billings
State or Province: MT
PostPosted: Thu Nov 19, 2020 2:15 pm    Post subject: Reply with quote

As a followup report, I replaced the antenna connector and got the slightly better (but not acceptable) SWR--around 5.0. I got a jumper to connect my Standard Horizon portable to the fixed antenna, and got a 1.2 SWR. This does seem to imply that the fixed Cobra radio or its connector is leaky, wouldn't it? Maybe too many hours in the salt air?
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thataway



Joined: 02 Nov 2003
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PostPosted: Thu Nov 19, 2020 2:27 pm    Post subject: Reply with quote

Any idea on the year or model of the Cobra Marine VHF radio? How does it transmit to the hand held? How about receive the weather or CG? (The Sea Tow Radio Checks are no longer available I am told.
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Ken O



Joined: 05 Mar 2014
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City/Region: Billings
State or Province: MT
PostPosted: Thu Nov 19, 2020 2:34 pm    Post subject: Reply with quote

The Cobra radio is an MR_F55. It has DSC, so it has to be 1992 or newer. I'm a bit away from the Coast Guard in Montana, and I don't want to transmit much for testing, but the Cobra with the Shakespeare antenna does pull in our local NWS station better than anything else I own. I think transmit is a better test, but I might have to wait until I get the boat in the water.
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thataway



Joined: 02 Nov 2003
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Photos: Thataway
PostPosted: Thu Nov 19, 2020 5:25 pm    Post subject: Reply with quote

If it were a 55 D it would be after 2011--with out it is prior to 2011. (D designates that the radio has a separate DSC channel 70 receiving section.)

Although not 100% legal, as long as you are not near any critical FCC licensed equipment or Utility operation area that is using RF close to Marine VHF frequency, you can use the hand held VHF as a platform. Go 100' away, 200' etc and see if your partner can hear your signal from the boat radio...etc. Then visa versa--to see how far the hand held VHF will transmit, and then see of the boat radio will be picked up by the VHF. Should be several miles, Just say "Testing Marine VHF equipment"! Use Channel 68 for example.

There are ways of testing the VHF marine radio, but beyond even many radio operator's capability. Most VHF marine radios will shut down the output if the SWR is much greater than 2:1. Thus you won't get much if any signal output.

How were you connecting the hand held VHF to the SWR meter?
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