Last VHF question--I promise!
 

I have a 5' CB whip antenna lying around. If I hooked that up to my VHF radio on the boat, would it work?

And, where's the best place in the Lakes Region to pick up a 3' whip antenna and stainless mount without paying a 200% (st)ealership markup?


Thanks

Not very well. CB radios operate around 27 MHZ and Marine VHF is around 156 MHZ. It may do something but a coat hanger would work as well. In the extreme case, it could damage your radio.

In the lakes region, you will have a problem getting stuff like this mark-up or not. If I had to buy it locally, I'd call all the marinas, and visit only the biggest stores. I'd really try to but it over the internet, there just isn't much selection of marine electronics in any retail store.

As JRC said, antennas are designed for specific frequenc(ies).

Take a look at Radio Shack, they have some nice prices for web only deals and one antenna available in (some) stores.

Check 'em out online.

I thought as long as an antenna had a certain amount of resistance (I think most VHF antennas are 50 ohms), it would not damage anything.

..And it would operate efficiently if the length of the antenna "matched" the length of the wave?

Airwaves? Where are you???

This place is my favorite.

http://ecatalog.westmarine.com/

You may be able to use this next place against the first with price matching.

http://www.consumersmarine.com/

I'd love to do business locally, but pricing must be within reason on this stuff.

Antenna stuff
 

The correct term here is impedance, not resistance. A huge difference when disscussing AC components versus DC.


In order to be a match (show the correct impedance of 50 ohms) the antenna's "electrical" length must match that of the output of the radio. That output is determined by frequency. (that is why you usually see antennas rated as 1/4 wave, 1/2 wave or full wave in design)

A CB antenna is electrically matched to show 50 ohms when it's length matches a certain fraction of the wavelength of 27 mhz. A VHF marine antenna therefore shows a 50 ohm impedance in the 156 mhz range.

Connecting a VHF radio to a cb antenna will cause no harm while it's receiving, although receive range will be greatly diminished. When you transmit however the impedance mismatch will cause much of the RF energy to be reflected back into the final output stage of the transmitter, While most modern transmitters have protection that will shunt this or decrease output power, continual usage will most likely result in damage.

Winni,
You pretty much have it right, the antenna must have the right resistance and the right wavelength. But the devil is in the details.

In the radio frequency world, resistance (ohms) is not accurate enough, you need to consider impedance as well (also ohms). You can think of impedance as resistance that changes with frequency. So a 50 ohm antenna at 27 Mhz is likely not 50 ohms at 156 Mhz. As Skip says, your radio is designed to have 50 ohms and with the wrong antenna it won't see 50 ohms.

Second thing is wavelength. The length of radio waves is inversely proportional to frequency. So at 27 Mhz your wavelength should be around 36 feet and at 156 Mhz its closer to 6 feet.

WOW Skip!

I didn't know you were a radio engineer. Another thing we have in common.

Electronics stuff....
 

In my cold war life electronics (and underwater acoustics) is what I specialized in when I served in the submarine service. I was a sonar supervisor on a Fleet Ballistic Missile Submarine (U.S.S. James K. Polk SSBN 645). Now a-days I have a side business where I program (and service) many of the Motorola digital radios issued statewide the last decade, emergency vehicle electronics upfitting and auto/marine electronics. I have recently branched into point-to-point wireless and wifi installations. Currently have configured a point-to-point system and am starting to implement wifi throughout a major campground.

I have toyed off and on with the idea of offering mobile marine electronics service to the Lakes region, but I am still working out the logistics as this is an hour away from my main service area (Strafford & Rockingham counties).

I hope to bend Don's ear at forum fest about some potential advertising I may want to do via this website...seems to be plenty of potential customers here...:)

Anyway, I am working into this gig gradually as I still plan to do a few more years in my Government job....this is definitely not the time to retire!

On the wireless stuff, I have c-level contacts at Firetide, Azalea and Fluidmesh if you start looking at mesh topologies. I also have a distributor in Chicago that specializes in wireless (they are a disti for our cameras as well).

Funny you mention the marine electronics/upfitter biz. I was looking at a couple of properties with lake/dock access for a similar reason. We should talk...

Small underwater world!
 

Hey Skip:

I used to service the Polk when I was stationed on the drydock in Holy Loch.

Misty Blue

Warning!...:offtopic:

USS Canopus?

USS Holland?

:look:

Gee, do I get to thank you for all the goats milk they always gave us there? :D

Excuse me for bringing this up, but isn't the Winnipesaukee vhs radio talk just a couple-three-four salmon fisherman who are out there troll'n around at 1.5 mph, tell'n some fish stories over the radio.

Like no, we ain't be catching nothing here, the fishing stinks....how 'bout you....catch anything? Nup...nuth'n here either! Dr Hook has headed over by Diamond Island..... following him back 'bout quarter mile.....yeah!:cool:

FLL, yes that's about all the chatter you hear these days. All the drinking buddies have switched to cell phones for obvious reasons. Everyone under 30 has a cell phone grafted to their ear at birth. Kids under 20 can't talk, they can only text. :D:D:D

I still haven't installed a permanent VHF on my boat (I use a hand held). I boat strickly on Winnipesaukee and VHF is becoming soley an insurance policy or a novelty during fishing derbys.

Me, too! and other VHF radio stuff...
 

I too am an RF engineer, though these days I deal more with fiber optics (who says data at 10 or 40 Gbits/second isn't just like RF?).

I spent over 20 years on radar systems and missile guidance systems working for Raytheon.

Like JRC, I also use a handheld on Winnipesaukee, though I do sometimes use the antenna mounted on the boat to extend the range. (I've rarely been unable to reach the Marine Patrol using the rubber duck, but it's nice to have the better antenna available if I really need it.) I also bring along my dual-band (144/440) ham handheld, but mostly for 'rag chewing' when I'm at anchor and kicking back a cold one (usually a Dr. Pepper).

Didn't realize that there were a whole lot of HAMs out there on the lake. Hmm.. may have to bring the 2M rig out with me next time. Doesn't seem like there are a whole lot of people out there at least on the Ossipee machine.

As already stated the antenna has to be matched to the radio and while as Skip says most radios do have some protection against a mismatched antenna most are not resilient to take to much of that, especially if they operate at high power. Once you fry the finals the radio is good as junk, 99% of the time it's not cost effective to fix them once that happens. Even if you get a marine antenna it's always a good idea to have somebody check the match on it before using it just to be sure. Plus the closer you are to a 1:1 match to the middle of the operational band spectrum you're sure to get the best performance out of your rig. Then again is it even possible to trim those glass marine whips if needed? Hey one question on that since I have too considered getting a marine radio in my boat, what do you use for a ground plane?

Antenna gound plane
 

Most of the fiberglass marine antennas don't require them as they are designed to operate as a half-wave dipole, with either a single or dual dipole element (dual dipole element antennas are usually configured as a collinear array). Remember, a dipole doesn't require a ground plane to radiate efficiently.

On the other hand, the base-loaded stainless steel whips do, but many of them are designed to be mounted to a railing, which acts as the ground plane. The radiation pattern won't be circular, but it will radiate better than the leaky dummy load that is the rubber duck antenna. Those antennas not mounted to a nice conductive railing will require some kind of ground plane, whether it is a plate or wire radials on the other side of the deck where the antenna is mounted.

I too made the switch from RF to optics engineering. I worked on microwave digital radio, then CATV stuff, and for the last 12 years DWDM gear. DWDM is just like CATV, only lots faster. Oddly, it's the backbone for FIOS.

Verizon is one of our customers, as is AT&T, Quest, ComCast, MetroCast, Sprint, FairPoint, Frontier, Cox, Time-Warner, BT, and a whole host of other telcos and Cable MSO's all over the world. We deal a lot with FTTH, CWDM, DWDM, PNG, and utilities, too.

These days most of my RF experience is with ham radio, VHF marine, and some military systems.

I must admit I do have fun with it. I like to listen to Channel 16 on the scanner at home. It never ceases to amuse/amaze me the things I hear going on around the lake!

Sounds like we work for the same company... My office is in Westford MA.

Are you on Robbins Road?

are you guys LUsers? :eek::eek:

Yup. I am indeed. 25 years now with this employer.

I work for a small fiber optics test equipment design/manufacturing firm in Belmont, NH and the main offices of our corporate masters are down in Spartanburg, SC.

Formerly a LUser, before that, AT&T/Bell Labs, now Alcatel-Lucent.

Wow
 

Not for nothin' guys, but this is fascinating....

BT

Not since 2001. When I started the company was called "Cascade", and it was a fun time to be in the business.

I served my time at the big red circle through an aquisition as well. And left in 2001. Given your Cascade time, we probably know some of the same people.

Yes a much more fun time to be in the business.

I thought I was pretty savy with most things mechanical but I've met my match on this thread.As my father always said."the more you learn,the more you find out how much you don't know".I feel I'm getting dumber.:confused::D:laugh:

Me too...
 

I'm with you SS. I've done more than a few installs of CB/UHF/VHF radios and antennas over the years in trucks and public safety vehicles and "understand" most of what has been stated here in this thread, but these guys are in a league all their own and I'm not afraid to say I learned something. Very cool. Thanks.

Blue Thunder

It is a small world (after all) ...
 

Hmmmm WE, sounds like we might have crossed paths in our former careers. Did you work for P. Ventresca ?


How's that tune go ....