[Boatanchors] Drake cable question (measured)?

Wed Jun 11 13:54:02 EDT 2014

Ron -

Au contraire!

First of all, 'RG-6' doesn't mean anything.....  It's a holdover from a military standard that 
DID specify characteristics, but is no longer effective.

There a several 'kinds' of RG-6, depending upon who sells it and what it is intended for.

The cheapest type, probably what you get from Radio Shack and Cables-R-Us outfit, is a steel 
center conductor with a thin copper plate, 60% shield coverage braid, and an aluminum foil outer 
shield.

The stuff sold for burial has a gel injected dielectric to discourage water ingress.

The best stuff has a stranded copper center conductor, a gas injected foam dielectric, and a 
full braid and aluminum foil outer shell.  This is probably closest to the original 'real' RG-6, 
although I haven't checked that.

Yes, the copper clad steel center conductor version is reasonably low loss 'up to 2200 MHz' as 
you say.   However, below ~7 MHz the loss (specifically center conductor) increases due to skin 
effect.  The 7 MHz figure is for a specific copper plate thickness, but you can bet the 
'bargain' boys are making that copper plate a little over a micron thick!  It only has to look 
like copper down to 50 MHz or whatever the bottom end of the cable TV band is.

Taking it on down to about 1 MHz (or 1 kHz?) used in your bridge, is ALL in the steel, which 
'may' account for your 'Lo-Q' (broad) dip!

So...  The PreMixer signal for the stock 4-Line radios runs from 7.145 MHz up to 35.605 MHz.  So 
it's probably ok, but NOT optimum, depending upon which version you happen to get.

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>

Ron Bussiere via Boatanchors wrote:
> Richard, thank you for the tip about the periods. I knew there had to be a way...
>
> One last thing on the cable, since this poor equine has been flogged enough.
> I do have 2 Q Meters. A nice GR and a Heathkit. I didn't even think to measure the Q of the cable.....
>
> Lastly, what is strange about the RG-6 cable, is this stuff is supposed to be good to 2200 MHz, so it can't be too lossy... ha ha
>
> ron
> N4UE
>
>   
>
>   
>
>   
>
> -----Original Message-----
> From: Richard Knoppow <1oldlens1 at ix.netcom.com>
> To: bonddaleena <bonddaleena at aol.com>
> Sent: Wed, Jun 11, 2014 12:42 am
> Subject: Re: [Boatanchors] Drake cable question (measured)
>
>
>
> ----- Original Message -----
> From: <bonddaleena at aol.com>
> To: <1oldlens1 at ix.netcom.com>; <boatanchors at mailman.qth.net>
> Sent: Tuesday, June 10, 2014 2:26 PM
> Subject: Re: [Boatanchors] Drake cable question (measured)
>
>
>
>   Hi Richard, no,it doesn't measure df. I used extreme care
> dressing the VERY short leads from the Leader to the cable
> under test. I repeated the tests multiple times. I use this
> bridge to measure ePay, er, eBay variable caps for the new
> VHF linears I am building (someday) ha ha
>
> I have used this bridge hundreds of times and measuring the
> RG-6 was the only time I have ever seen this broad null. The
> 'tuning knob' is a 10 turn pot and it's easy to find a
> normal cap's value.Normally, the 'dip' is extremely
> sharp.......It went back to Leader a couple of years ago due
> to trying to measure the value of an 'orange drop'... Long
> story, but funny and expensive!!!
>
> I don't know what to say... I'm sorry about the results. I
> should have used a different format. What I typed in is NOT
> what came out!
>
> It's worth everything you'all paid for it.... ha ha
>
> ron
> N4UE
>
>
>      I didn't mean to sound critical, I was only trying to
> figure out what happened.  It would be interesting to
> measure this cable on a regular impedance bridge like the GR
> bridge or even on a General Radio XY bridge. The latter is a
> PITA to use but will balance on anything including negative
> values.  I suspect the cable may have some sort of loss that
> is keeping it from balancing on the capacitance meter.
> Since you are measuring open circuit this may be loss in the
> dielectric (would have to be large). Very odd. Anyway, I
> don't think I would use this cable for anything.
>      I found for sending tables in text its sometimes helpful
> to use rows of dots.  I discovered this when posting
> photographic developer formulas.  A sample
>
> Kodak D-76
> Water (at about 125F or 52C)................750.0 ml
> Metol.........................................2.0 grams
> Sodium sulfite, desiccated..................100.0 grams
> Hydroquinone..................................5.0 grams
> Borax (granular)..............................2.0 grams
> Water to make.................................1.0 liter
>
> Use full strength of diluted 1 part stock to 1 part water.
>
>      Usually this arrangement will hold together even when
> the format is changed.  Let me know how it comes through.
>
>
> --
> Richard Knoppow
> Los Angeles
> WB6KBL
> dickburk at ix.netcom.com
>
>
>
>
>   
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