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Catalina/Capri 25/250 Sailor's Forums

Catalina 250 Specific Forum

VHF masthead mount

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sterngucker
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USA
169 Posts

Initially Posted - 10/03/2006 : 19:01:01

I know this topic has been discussed in the past but the search engine won't look any further back than 06/30/06. I am finally installing a masthead VHF antenna, the Shakespeare squatty body. I have decided to attach it using the upper shroud bolt. Is there any problems with this location? Also, to run the wire down the mast I have removed the mast truck and see the tube for the wire run. Do I need to drill out the rivets holding the foot of the mast to run the rf cable or is there an alternate method. Thanks for any and all assistance.

Charlie
"C Angel" 250WB #799

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britinusa
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USA
5404 Posts

Response Posted - 10/03/2006 : 21:34:54

Hi Charlie,
we did exactly that same mod.
I took the mast head off so that I could manover the cable into the tube.
Used a wire snake to thread down the mast inner tube. Drilled a small hole large enough for the rubber grommet and the cable. Didn't need to remove the mast foot.
The only challenge was to get the cable out through the hole, so I think I pulled it up the mast after feeding the snake from the head towards the foot.
I was able to snag a thin line loop that I put on the end of the snake and pull that out of the hole, attached it to the cable then pulled the whole thing backup the mast.
I used a small bracket and the existing screw holes on the mast head to hold the antenna.

Works a charm.

It was much more difficult running the cable from the deck connector back to the vhf set.

paul

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Turk
Admiral

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USA
736 Posts

Response Posted - 10/04/2006 : 11:17:50

Remember to offset your windex if you have one up there. It won't turn with an antenna in the way!

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Bubba
Admiral

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USA
542 Posts

Response Posted - 10/05/2006 : 18:04:01

Drilling out those two pop-rivets is not a big deal if the mast is already down. You'd need a pop-rivet tool to replace 'em though. Those rivets' only function to keep the foot from falling off when the mast is unstepped.

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Tom Potter
Master Marine Consultant

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USA
1913 Posts

Response Posted - 10/05/2006 : 18:15:39

Make sure you get 2 rubber mast grommets to keep you coaxial from chafing. You can get just about everything you need from Catalina Direct including the grommets.

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528
Navigator

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USA
181 Posts

Response Posted - 10/05/2006 : 21:10:32

I installed mine 3 yrs ago. Drilled a hole through the antenna mount plate and used the forward mast truck pin to mount. It orients with forward sweep and does not interfere with a windex. I'm not sure if I have a pic. I mounted it on the port side. Easy to remove the antenna when the mast is down.

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528
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USA
181 Posts

Response Posted - 10/05/2006 : 21:14:14

I do have a pic !!!

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frog0911
Master Marine Consultant

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1349 Posts

Response Posted - 10/05/2006 : 23:14:32

Here is my setup. The bar going out off the back of the masthead is the windex offset mount.

Black cable is antenna, gray is lights.

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britinusa
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USA
5404 Posts

Response Posted - 10/06/2006 : 06:36:13

Frog, how do you disconnect your vhf coax when lowering the mast? The deck connector appears to be a bulkhead passthough.

Paul.

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frog0911
Master Marine Consultant

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USA
1349 Posts

Response Posted - 10/06/2006 : 08:13:41

Don't disconnect it. Don't have a trailer. Don't have a vechicle to pull one. The boat sits 530 feet from the back door with access to the St. John's River and ICW and time is not a factor in going somewhere since I retired the second time.

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Nautiduck
Master Marine Consultant

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USA
3704 Posts

Response Posted - 10/10/2006 : 14:16:00

My new C250 has a masthead mounted VHF antenna but it just has the squatty stub, not the actual 3' entenna which would screw onto it. The previous owner said with the VHF antenna stub up that high, the actual antenna isn't needed. Anyone ever hear of that before?

Thanks. Randy

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sterngucker
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USA
169 Posts

Response Posted - 10/16/2006 : 16:54:15

Thanks to everyone for all the great help. Here are some pics of my antenna installation. I utilized the existing upper shroud tang and put a rivet in the bottom hole of the antenna mount so it wouldn't swivel. Had a bear of a time getting the cable down the inner tube in a few spots. I need to test the mast lights to make sure other wires didn't get pulled off in the process, although, according to the ohm meter there are no open circuits between all four pins.

Now I am in a bit of a quandry as to the best method for going through the deck. I am looking at the two choices below.

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frog0911
Master Marine Consultant

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USA
1349 Posts

Response Posted - 10/16/2006 : 19:12:27

I prefer the bulkhead connector for two reasons:
1) Smaller hole through the deck.
2) More top deck covered surface for a better seal.

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">The previous owner said with the VHF antenna stub up that high, the actual antenna isn't needed. Anyone ever hear of that before? Thanks. Randy<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

I have been trying to remember from my radio training about base loaded antennas, and if I remember correctly the antenna length required for VHF is 6 feet for proprer impedance match for the frequencys. Since there were areas requiring a shorter verson the base loaded coil came into being. The purpose of the base loaded antenna was to allow a shorter whip, but still give the proper feedback to the radio so it thinks the antenna is 6 feet long and thus proper impedence match and max power output. If you know a HAM operator he would more than likely have a standing wave meter that you could borrow or would come measure the standing wave of your antenna both with and without the whip. The standing wave for a perfect match is one to one, anything different will degrade your power output and thus distance capability.

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Tom Potter
Master Marine Consultant

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USA
1913 Posts

Response Posted - 10/16/2006 : 19:30:45

Here's a picture of the "port" deck connector as you described in use. I soldiered my coaxial to the connector, it was a interesting job to say the least.

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sterngucker
Navigator

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USA
169 Posts

Response Posted - 10/19/2006 : 12:33:54

Tom,
In your picture I see you have white washers on each screw of the bulkhead connector. Are these to help seal the holes or to prevent dissimiliar metal corrosion, or both? Just curious. I could not find a "marine" version of that bulkhead connector on the internet or the West Marine catalog, so I am going to use the one I got from Radio Shack and seal it real good. Thanks again.

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Tom Potter
Master Marine Consultant

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USA
1913 Posts

Response Posted - 10/20/2006 : 17:38:11

Charlie,
My connector was not "a marine version" either, just one I ordered off the web. I think it had a silver coating or something like that on it to help when I was soldiering the coaxial. (Or at least that's what the guy told me when I bought it.)

The little "white washers" is actually 3M-4200 I used to seal it. I put lots of 4200 around the screws and around the connector.

I have a rubber end cap like goes on the foot pop top legs that fits over the threaded part of the connector when I have the coaxial disconnected to keep water from getting in it.

I believe your radio shack connector will work just fine.

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Turk
Admiral

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USA
736 Posts

Response Posted - 10/20/2006 : 22:15:20

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">[i]
Now I am in a bit of a quandry as to the best method for going through the deck. I am looking at the two choices below.

The bulkhead connector (to port) would require a smaller hole and let me snake a cable through the deck to where I could get a hold of it via the cabin swivel light hole.
The female barrel connector (to starboard) might be more resilient but require a larger hole. Tightening the nut on the inside from the afore mentioned hole and then attaching a male plug to the end seems much more difficult. What has been your experiences with this? Thanks again.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

I used one of the "clam" thru deck devices. That allows the antenna wire to go thru the deck without creating another 2 connections. The fewer the connectors the less problems down the road. Buy a big enough one to allow the your end connector to fit through the clam's hole. If you are wiring to a location that you cannot remove the wire when you take the mast down, I would go with your connectors for ease of removal when you take the mast down.

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Arlyn Stewart
Master Marine Consultant

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USA
2980 Posts

Response Posted - 10/21/2006 : 09:01:29

Tom makes a good point about SO-232 and PL-259 connectors. The common variety found at radio shack are nickle plated brass. They are cheap so are popular but are not near as good as silver plated connectors.

Nickle plated connectors need the nickle plating filed off in the area of the solder holes including inside the holes in preparation for soldering the braided shield to a PL-259 connector.

Even so, soldering the shield to the brass requires greater heat and the greater heat melts the dialectric in the cable causing the inner wire and outer jacket to lose there intended seperation distance. This produces what is known as an impedance bump and will degrade the ability to match the antenna to the radio perfectly.

Many of the nickle plated connectors also use cheap plastic to hold the center conductor at the end and when overheated, it distorts or melts away. This probem is greatly magnified on cables with lower shield weave percentages because as heat is given to the braid... the exposed dialectric melts and contaminates the wire making it difficult to solder.

Much much better is to use a silver plated connectors. The solder will flow very easily on the silver plating and heat can be kept to a minimum when soldering the braid thru the barrel holes.

The other consideration to using nickle plated is probably not a big issue, nickle to nickle is not a good lubricant and the connectors do not screw smoothly together.

The one advantage of nickle is they look better than silver. They stay shiny and don't discolor whereas silver plated oxidise and discolor.

The SO 232 (not sure I remember the number accurate) base female connector has some issues as well. Extract some center conductor out of the shield by forming a loop and opening some braid and using an awl, pull the conductor out. The center conducter is soldered to the center pin of the SO connector and a eye lug is soldered to the braid and attached to one of the four mounting screws. It is important to keep the center conductor and braid as short as possible as the longer the seperation of conductor and shield... the greater the impedance bump.

It is also wise to use some dialectric greese both in the female connector and around the cable where the inner conductor is pulled out to protect from water migrating through the connector and following the inner conductor through the cable. Water causes the cable to be lossy, destroying the 50 ohm impedance of the cable and the SWR match of radio to antenna. Remember, an SWR match of antenna to radio depends upon a 50 ohm impedance transmition line with minimum bumps.

I agree that a chassis connector with the four mounting screws is superior to the barrel connector for this installation though both will work.

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