VHF antenna thru top cabin connector

[mk1]

I had recently found in my closet an old antenna I bought for something else, and decided to install it on my masthead. At first, I was also worried about losing the signal over a long cable and connectors. So, I decided to make a simple experiment. I invested $5 in a microwave detector. First I secured antenna and detector with clamps in a position that gave me about full-scale reading when I clicked transmit key (making sure radio is not set to channel 16), and tried different configurations: antenna connected directly to the radio with a 6 ft cable, then added 40' cable with one joint connector between 40' and 6' ends then the same 40' cable plus a 10' cable now with two joint connectors, one to connect the 6' antenna cable to the longer cable and one bulkhead connector to connect longer cable to a shorter cable. I saw a very slight power loss, roughly 10-15% when adding the first cable. One cable and two cables were about the same. My microwave monitor is not a very precise tool, but I am sure I would have noticed if I lost 50% of the power.

So.. I have concluded that it is OK to have a couple of connectors, and I did use them. I ended up with three cables and two joints. One longer cable inside the mast, then a bulkhead connector and finally about 10' inside the cabin. I do hear a lot more chatter now than I did before with a handheld VHF, but this could mean anything, may be people talk more. I plan to test transmission range some day, I need to find some one to call. And may be I will even learn one day how to use DSC calling.

[vizwhiz]

Great post mk1 (as in Spitfire Mk1?), and apparently a simple experimental tool...because in one sense, it doesn't really matter what a wattmeter shows as cable losses, it matters what is coming off the antennae. I wonder what 10-15% loss means in range in the sense of value and safety. To a hammer, that much loss probably is intolerable...but to us, it might not be that significant (i.e. compared to going from a handheld to what you have now). If the handheld was sufficient, might what you have now be considered overkill...??**


**Not to be misconstrued as assuming that a handheld would always be sufficient, nor that having additional range might in any way be a bad thing. Simply a question of pragmatism - where does one normally sail, what are the conditions, and was a handheld sufficient for that?

[Russ]

You know, I've looked at this mast/rail mount issue for a while and the only valid reason I can find for mounting VHF lower is in the event of a dismounting of the mast. Then a handheld would be a good backup or even a rail mount as backup.

EVERY powerboater I know is envious of sailboat antenna altitude. When line of sight is so important and more so than all 25 watts making it to the stick, why not mast mount? If you find yourself in some decent sized swells or far from shore, that 30' off the sea will push your signal so much further. Sure 30' will have some loss, but not as much as altitude.
Ever wonder how Coast Guard stations reach so far with only 25 watts? It's the tall tower.
I used to sail with a group of boaters on Long Island sound. We sailboats could talk to each other over MUCH greater distances than our stink pot buddies.

Just sayin'

[Hamin' X]

JSYK: Coax types from highest to lowest loss/ft:

• RG 58
  RG 8X
  RG 8 (213)

RG 8 has about 1/3 the loss of RG 58, with 8X somewhere in the middle. This is at 150MHz.

~Rich

[vizwhiz]

Rich,
I'm guessing that the RG 8 is the "U" designation? (Thanks for the input!)

[Hamin' X]

The letter that follows a cable type is used to indicate features that differ from the basic. An example is: RG-58/U is the standard. This means that it has certain physical and electrical characteristics, such as size and impedance. RG-58/AU has a stranded center conductor, instead of a solid one. Designations can vary widely from manufacture to manufacture. RG-8X for example, is the most abused designation out there and can vary from pure junk, to quality double shielded cable. I would stay away from it.

I have several recommendations on the subject that come from a commercial and ham radio perspective, not necessarily from a marine point of view.

• 1. Buy the highest quality cable that you can.
  2. Don't worry about loss in the cable, you will lose more signal in connectors and aging coax.
  3. Do not use foamed dielectric coax on a boat. The foam is open cell and WILL absorb moisture and the soft foam allows the center conductor to migrate towards the shield when making tighter turns. This causes an impedance "bump" in the line, which increases loss and other nasty things.
  4. Use stranded center conductor cable. It withstands vibration and constant flexing, where solid will fatigue and fail.
  5. And last, but not least: If at all possible, stay away from the PL259/SO239 type connectors; the type found on CB radios and the back of your VHF. It is just barely suitable for indoor use and if used outside, must be wrapped and waterproofed. Not good for trailering. Most on the market are cheap junk that will distort when soldered, or fall apart with use. If possible, have someone that knows how, install N type connectors and waterproof where the cable goes into the connector. [end rant]

Connectors and proper installation will contribute more to a long lasting and good performing setup, than low-loss-cable. I realize that this is not practical for all and not necessary for some, just my thoughts on the matter.

When I redo my installation done by the PO, it will be with RG-58/AU, from an American manufacture and rubber booted N connectors for the deck. Since the SO-239 used on the VHF radio is a permanent installation, I will have to use a PL-259 to mate to it. Likewise, the connector on most marine antennas is an SO-239, so will require a PL-259 on the cable. It will be wrapped with Scotch-33 tape and covered with self fusing butyl-rubber tape, for permanent waterproofing.

~Rich

[Catigale]

Ever wonder how Coast Guard stations reach so far with only 25 watts? It's the tall tower.

..and a few more watts to I think....Im guessing kW or more....

[Russ]

Ever wonder how Coast Guard stations reach so far with only 25 watts? It's the tall tower.

..and a few more watts to I think....Im guessing kW or more....

Not to my knowledge. Coasties are limited to the same 25 watts as we are. But their towers are much higher and cables are top quality. VHF is mostly line of sight and altitude wins over wattage most of the time.
So, in a perfect world, use top quality cable (see Hamin's comments above) and mount that sucker up high. Not that a lower mount is bad, but higher is superior in most quality installations.

[mastreb]

Navy and coastguard VHF (referred to as bridge-to-bridge) in the Navy similarly limited so as not to destroy civilian receivers close by. For long range, they use HF transceivers that are optimal in over-the-horizon frequencies (3-30 MHz), xmit in the KW, and have a useful range up to 8000nm.

Matt