Bulk Purchasing and Buying Power - MkII

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marisca
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Bulk Purchasing and Buying Power - MkII

Postby marisca » Wed Dec 30, 2015 5:43 pm

Having submerged my mast vhf aerial connector (don't ask) and turned the braid an interesting powdery black colour, I have given up relying on the mantra that the signal flows over the outside of the conductor and I intend to purchase about 15m of RG-8U cable.

Price seems to be about £150 for 30m (RS); any taker for 15m? or does anyone know a better source?

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Re: Bulk Purchasing and Buying Power - MkII

Postby Silkie » Wed Dec 30, 2015 7:59 pm

Obviously I know better than to suggest an alternative but just wondering why you've chosen RG-8/U over RG-8X which most seem to recommend and is available by the metre for about £3?
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Re: Bulk Purchasing and Buying Power - MkII

Postby marisca » Wed Dec 30, 2015 8:43 pm

Always ready to listen to advice (before ignoring it - according to my wife!). RG-8U attenuation is about half the dB of RG-8X - maybe not that important over 15m but given my skills with soldering connectors, every little may count. My interweb skills seem inadequate at identifying stranded central conductor, all tinned, 50 ohm cable of RG-8X without going to the colonies even the eBay stuff is septic. Maybe I should just ask Salty John.

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Re: Bulk Purchasing and Buying Power - MkII

Postby marisca » Wed Dec 30, 2015 9:30 pm

Just checked Salty John's site and he is out of stock of RG-8X, though he does have RG-213 at £156 per 30m. That's 9.5mm dia. cf 7mm for RG-8X.

That would still leave 15m for someone else.

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Re: Bulk Purchasing and Buying Power - MkII

Postby Pilgrim » Wed Dec 30, 2015 10:40 pm

It is worth shopping around. Maplin are offering RG213U if you are prepared to buy 100m at just under £2.10 per metre. This is certified to the relevant US military specification so should be Ok.

The main area for losses even at the relatively low frequencies of vhf are the connectors. Avoid UHF connectors ( they were designed in the 1930's and their performance reflects this) and go for n type or bncor tnc for any cable joins. Make sure you buy the right connector for the cable you have. I prefor the solder type rather than twist on as I feel that even though they are more time consuming to fit they are less subject to corrosion in the marine environment.

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Re: Bulk Purchasing and Buying Power - MkII

Postby Silkie » Wed Dec 30, 2015 11:46 pm

The U probably weighs about 3x the X and I would have thought those extra kgs up the mast would have been important to a racing man. :)

I have a continuous run from masthead to VHF and remake the VHF end at the start of each season - reduces the chance of water ingress and probably compensates for some of the attenuation differential.

I hope this doesn't sound like I know what I'm talking about. :oops:
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Re: Bulk Purchasing and Buying Power - MkII

Postby sahona » Thu Dec 31, 2015 11:50 pm

I had a similar bout of 'blackbraiditis' and just used the normal skinny stuff. If the aerial is good quality (Salty John - Metz works for me) you can't make it any better than line of sight no matter how much power you fire up it.
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Re: Bulk Purchasing and Buying Power - MkII

Postby mm5aho » Fri Jan 01, 2016 12:18 pm

I have a part drum of coax at home. I forget which it is (and I'm currently in Lancashire), but I suspect RG mini-8. I'll look it out next week.
I've mostly bought coax from ham radio dealers, but it is quite a bit cheaper by the drum, say 100m. Buying cut lengths can double the price.
The issues to me are attenuation, outside diameter (got to get through glands etc), connector availability and price, and cable price. Cheaper versions typically have very poor braid density. Some have nasty foam dielectric which melts on soldering the centre core, some have nice high temp plastic of some type. I have a lot of Andrew heliax at home (FSJ4-50, LDF4-50 and LDF5-50), but that's not much use for this application.
Buying a larger quantity of suitable coax sounds to me a good cooperative buying project.
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Re: Bulk Purchasing and Buying Power - MkII

Postby mm5aho » Fri Jan 01, 2016 12:25 pm

Geoff.
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Re: Bulk Purchasing and Buying Power - MkII

Postby marisca » Fri Jan 01, 2016 9:30 pm

I am getting less certain by the minute. If only all cable specifications were written using the same units and at marine vhf frequencies. Anyhoo, in amongst the specs I have .....
ISAF in its Offshore Regs 2016-2017 requiring a power loss of <40% for a masthead antenna and co-axial feeder cable - they used to prescribe cable types with RG-213 recommended but that has gone.
Then I found a table which for a 15m run at 150 MHz gives RG-58C/U a 51.7% loss and the fatter RG-213 a mere 26.2% loss. Given that I have 6 connectors in my system - 1 hidden behind the radio; a pair that allow alternative connection to the pushpit aerial; another pair at the mast base; and the connection to the mast-top aerial - I feel I need the best cable possible and, if I take Mark's advice, the PL259/barrel combinations may need to go, though Amphenol seem to suggest that at <200MHz the N-type or TNC are overkill.
.......... And to think I used to use choc-block or just twist the wires together.
If anyone feels capable of offering advice, I'm listening!

Meanwhile I have an 2 off old reels of un-tinned solid core RG-59B/U (ideal if it wasn't 75 ohm); remains of a reel of 22awg shielded tinned twin core and earth (ideal for old Sea-Talk or NMEA 0198) - don't particularly want rid of them but reasonable lengths are available to the needy.

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Re: Bulk Purchasing and Buying Power - MkII

Postby mm5aho » Sat Jan 02, 2016 7:13 pm

RG mini-8 has similar attenuation to RG213, but at the smaller outer diameter.
What length do you need?
I have lots of various coax leftovers from projects. Solid core coax is to be avoided, in installations where there's movement of the cable, much more liable to break. Stranded centre core much better.
Amateur stuff for the 2m band is similar attenuation figures to marine (145 vs 156MHz).

What length?
Geoff.
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Re: Bulk Purchasing and Buying Power - MkII

Postby marisca » Sun Jan 03, 2016 10:40 am

According to the Nevada website their Mini-8 Super XX has 10.5dB/100m attenuation at 100MHz while their RG 213 has 7.2dB. The fun thing being that different manufacturer/suppliers quote different numbers for the same wire designations.
The question is - for my noddy application of 25W, 150MHz, 15m run with 6 connectors, does it really matter? I had hoped some others would be rewiring their mast and a 100m reel would make sense. The one thing I have out of my interweb wanders is the price variability (from £1 - £6 per metre for nominally the same cable) and that the 100m drum doesn't make much, if any, difference for some suppliers.
So, my apologies for wasting your time; my thanks to Geoff for his kind offer; but for the minimal cost involved (~£20), I think I'll go for 20m of the RG213.

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Re: Bulk Purchasing and Buying Power - MkII

Postby claymore » Mon Jan 04, 2016 11:15 pm

marisca wrote:Just checked Salty John's site and he is out of stock of RG-8X, though he does have RG-213 at £156 per 30m. That's 9.5mm dia. cf 7mm for RG-8X.

That would still leave 15m for someone else.


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Re: Bulk Purchasing and Buying Power - MkII

Postby marisca » Tue Jan 05, 2016 12:52 am

Many thanks, Claymore. I'm afraid your neighbour's price was a wee bitty steep even though it is for connection to one of his excellent Metz aerials.

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Re: Bulk Purchasing and Buying Power - MkII

Postby claymore » Tue Jan 05, 2016 9:01 am

Ok - I use a metz myself and as you say, excellent.
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