VHF Connectors

[Tsatzsue]

I am in the process of relocating my VHF antenna to the masthead. I was wondering if anyone knows if there is a reason why I shouldn't use standard cable connectors at the places where I have to splice the cable? I am going to solder everything and have access to these fittings. The antenna and radio connections are going to be the standard VHF.

 

[Don S/V ILLusion]

Don't even think about it! Proper coax connections preserve the characteristic impedance of the line and antenna which must be precise. If not, you risk damaging the transceiver or, at a minimum, creating a severe mis-match such that the output power of the transceiver decreases.

Even a 1 dB loss in a connection means you lose 20% of your transmitted signal and a generic splice such as you contemplate will be far greater than that.

A huge false economy not using the proper connectors which only cost a few dollars at most.

 

[Maine Sail]

Don't even think about it! Proper coax connections preserve the characteristic impedance of the line and antenna which must be precise. If not, you risk damaging the transceiver or, at a minimum, creating a severe mis-match such that the output power of the transceiver decreases.

Even a 1 dB loss in a connection means you lose 20% of your transmitted signal and a generic splice such as you contemplate will be far greater than that.

A huge false economy not using the proper connectors which only cost a few dollars at most.

Yep just re-wired a mast last week and had under $20.00 into all the PL-259 VHF connectors & the splice, from the radio all the way to the mast head. Of course you really need to know how to solder these things, out doors in 15 knots on a rainy day, and the vast majority do not. Perhaps 95% or better of the VHF connections I come across are improperly soldered and test horribly, it's usually the braid.

What ever you do DO NOT use those gold Shakespeare terminals that cut through the jacket to make contact with the braid, they are joke.

I prefer the crimp/solder connectors where the pin is soldered and the braid is crimped. Easy, repeatable and I have never had one fail if done correctly. You also want to the biggest wire you can fit for the best performance. At a minimum an RG-8X or better for a 25' boat... LMR-400 or 9913 cable are probably out of the question on a 25 footer...

 

[Dan Hill]

Would you recommend dialectic grease on these connections?

 

[Maine Sail]

Would you recommend dialectic grease on these connections?

I don't use it, but I do use DeoxIT Shield. There is a study out there comparing dielectric to no dielectric on antenna connections and the dielectric is argued to cut into performance. There are also studies that contradict that one. I just put together clean connections, with a little DeoxIt Shield or DeoxIt D5 and then 100% seal them with self vulcanizing tape or a good electrical tape like 3M Super 88.

There is nothing wrong with applying dielectric grease but then it is nearly impossible to seal it with tape because nothing really sticks to silicone.

 

[Dan Hill]

Thanks for the info MS and apologies to tsatzsue for the thread hijack.

 

[Dan Hill]

Thanks Don, always a wealth of good advice here.

 

[Bill Roosa]

Hey tsatzsue
You do need to use the UHF connectors and I'm with Don on the dialectric goop being a weather proofing means. You also need to understand that that coax you buy at radio shack is 75 ohm and will work horrably in your 50 ohm impedance VHF antenna. you will have to go to the ham radio sites for 50 ohm cable and you should not skimp on the quality. with a 40'ish run from vhf to mast head your line losses can go as high as 5 db with the lower quality cables. that is a loss of around 3/4 of your power when you transmit (25 watts --> 6 watts)

 

[Tsatzsue]

I appreciate all your input and am amazed at how awsome this site is for help. I am heading your recomendations. I have some good communication cable and I am going to purchase the rest of the connectors. I have Sea choice connectors. Unfortunately they do not come with any installation lit. I plan on soldering everything then heat shrink. No problem on the Hijack. I have gotten my pe-pee slapped for that myself.

 

[Bill Roosa]

Again, it does not matter how fine your communication cable is if it is 75 ohm impedance.
You need good 50 ohm impedance cable, no options.

 

[kenn]

MS and I are of different schools of thought. I have used dielectric grease on all exterior coax connections for decades. I agree it doe not itself conduct but it isn't intended to in this application. It does permeate all voids thereby precluding moisture penetration while not creating any shorts between the coax dielectric, shield and center conductor.

I guess the best you might take from these opinions is that you probably won't go wrong either way.

I was initially confused on what is meant by dielectric grease... now I'm a bit better informed. At least with regards to silicone-based products.

... but still a bit confused. I currently use Grote Ultra-Seal on external connectors like mast lighting and trailer lights. It doesn't actually say 'dielectric' on the tube, but I've seen it referred to as a dielectric grease elsewhere on the Inter-google. This Grote stuff is apparently ok to apply on contacts, presumably because there's enough wiping action or contact pressure to displace the fluid. Anyway, it has worked fine for me so far.

 

[Forrest15112]

I'm not sure what you mean by standard cable connectors where you splice the cable. To me, standard cable connectors are VHF connectors screwed together. That's fine, but each one will add about 0.2dB of loss if done properly. You aren't limited to just pl259's which are very difficult to solder properly. N connectors are easier to put together, generally less lossy, but more expensive.

The dielectric grease is useful on threaded connectors, but not necessary if properly sealed. I wouldn't get it anywhere near the braid or center conductor of the coax cable though for the same reasons mentioned by MS.

The cable loss is something to keep in mind, but your choices ( cost) are pretty good at VHF. I like LMR240 cable. It's about the same size as RG8X, but has much better loss figures and is reasonably priced. At VHF frequencies, the loss with LMR240 is 3dB per 100'. RG8X-5dB, & RG58u is over 6dB. RG8x and RG58u are typical of the types found at Radio Shack. A good rule of thumb with regard to this term for loss is for every 3dB of loss, you effectively cut your power in half. 25w transmit power is now 12.5 at the antenna, 6dB loss would be 6.25, 9dB=3.125w and so on. Actual noticeable performance differences aren't as bad as that appears though. Typically, a receiver will require the transmitting station to increase it's power 3dB ( double) to notice a difference. That includes a station transmitting at 10 watts or 1000 watts. Every little bit does help and is compounded with cable losses and antenna gain.

Your antenna is probably rated for some degree of gain as well. This doesn't mean it amplifies your signal, but it redirects energy from useless directions, like straight up or down to horizontal. Picture a spherical ball and then a flat disk. The higher the gain, the flatter the disk. Some antennas focus the radiation into a single direction and extend their range even more in that direction.

If you have 3dB of loss in your cable, and 3 dB gain in your antenna, you end up with effecticvely the same signal as you would with no cable loss into an antenna with no gain. The gain vs loss does cancel out, but noise is increased and that reduces receiver performance. All in all, it isn't a big deal unless your cable runs are over 100'.

My point in this is to try to explain how it works and to let you know that the losses you are likely to incur on a 25' boat are not horrible, even with the cheap cabling. Installing connectors properly and good weatherproofing will be what makes it work best and last.