[Public-List] VHF cable

[Gordon Laco]

Good day friends, 

This talk of antenna cable reminds me of a discussion I had with my brother in law when he came aboard many years ago.     He is a professional in the commercial antenna business, serving radio and television stations, as well as his own very extensive Ham radio gear at his farm, which makes the place look like the ground station for the bad guy in a James Bond movie.

When I was positioning my VHF antenna, I thought I’d like to still have an antenna in the event of a dismasting, and wanted the simplest of ordeals when installing it.  The two objectives led to my putting it on the port stern quarter.   Yes, it’s not very high up, and in the reception department we find the weather station fades in and out as the boat swings at anchor due to the rig masking the signal, but it works well enough.

John, my brother in law, was horrified.   ‘Well enough’ was offensive to him, who reckoned that maximizing my radio’s performance was a primary concern.   He was about as offended by the antenna’s position as I would have been if he’d had a boat, and happily sailed it with empty batten pockets and a miss-matched headsail that didn’t fit. (which I’ve seen at our club)

Oh well.

Gordon Laco
Surprise 426




> On Apr 17, 2019, at 9:20 AM, Paul Wilson via Public-List <public-list at lists.alberg30.org> wrote:
> 
> I should mention than dB are logarithmic, so a difference of -3 dB is
> double the power loss. If your radio is rated at 25W at the transmitter
> output, 3 dB of loss means you're radiating 12.5W at the antenna.
> 
> Assuming your coax cable run is 50' (35' the up mast and 15' to your radio)
> the difference between LMR200 and RG8X is 0.4 dB. In terms of power ratio
> at 50' of run LMR200 = 0.64; RG8X = 0.58. Assuming 25W at the radio LMR200
> means you're radiating 16W with LMR200; with RG8X it's 14.5 W.
> 
> Quality and properly installed connectors that are well-sealed against
> water infiltration are also critical to long-term performance of the
> antenna and feed line. Water in the dielectric material (between the shield
> and core) is the downfall of coax cable. The February 2019 issue of
> Practical Sailor discusses this issue in some depth. They recommend "F"
> style connectors in lieu of the ubiquitous PL259/SO239 combo.
> 
> On Wed, Apr 17, 2019 at 8:31 AM Paul Wilson <dcmcrider at gmail.com> wrote:
> 
>> Here's a link to some coax attenuation charts, as well as cable diameters.
>> 
>> http://www.w4rp.com/ref/coax.html
>> 
>> LMR200 has 3.9 dB of loss per 100' at 150 MHz. (Marine VHF band is ~160
>> MHz.) RG8x has 4.7 dB/100'.
>> 
>> On Wed, Apr 17, 2019 at 7:27 AM Rod Symmes via Public-List <
>> public-list at lists.alberg30.org> wrote:
>> 
>>> RG8  and  RG8X are not the same item.
>>> RG8 is nearly 1/2" diameter, stiff and heavy.   8x is half the size and
>>> weight with ALMOST as low loss.
>>> I don't know the spec for LMR 200 to say how much of an improvement over
>>> RG8X it would be.
>>> 
>>> 
>>> Cheers,  Rod
>>> 
>>> -------- Original message --------
>>> From: Philip Bartlett via Public-List
>>> Date:16-04-2019 10:53 PM (GMT-05:00)
>>> To: Alberg 30 Public List -- open to all
>>> Cc: Philip Bartlett
>>> Subject: Re: [Public-List] VHF cable
>>> 
>>> You might want to use LMR 200. It’s lower loss, thinner and half the
>>> weight of RG8.
>>> 
>>> Philip
>>> 
>>> Sent from my iPhone
>>> 
>>>> On Apr 16, 2019, at 5:41 PM, Christian Douglas via Public-List <
>>> public-list at lists.alberg30.org> wrote:
>>>> 
>>>> I cut the existing VHF cable when I lowered the mast. Need to place a
>>> new
>>>> run to the top of the mast. The old cable is RG8X. Any thoughts on the
>>> new
>>>> cable? Any reason why I’d need a different cable?
>>>> 
>>>> Christian
>>>> Kittiwake #76
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>> 
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