[Boatanchors] Drake cable question (measured)

Mon Jun 9 17:34:31 EDT 2014

 Thank you Garey. As usual, you know your Drakes. Although I have been told I'm 'wasting' my time, it's my time and I made the following measurements using a Leader LCR bridge which was calibrated at Leader tracable to NIST standards. The results were verified with both a Boonton Lab Quality C Meter and a handheld Cap tool.
The cables were cut to 36.5 inches (just as a 'standard) and the extra 1/2 inch was prepped identically before connecting to the bridge.
This was 100% repeatable.

RG-8X (shielded)        spec = 25.0 pf/foot     measured = 25 pf/foot
RG-59 (shielded)        spec = 17.3 pf/foot     measured = 16.3 pf/foot
RG-58U                     spec = 28.5 pf/foot    measured = 29 pf/foot
RG-6U                       spec = 20.5 pf/foot    measured = 18 pf/foot  *
RG-62                       spec = 13.5 pf/foot     measured = 12 pf/foot
Audio cable                                               measured = 23 pf/foot  (.100" OD)
Phillips HDTV cable                                   measured = 16.6 pf/foot  **

* = this is Direct TV cable and quad shielded, of course. The notable thing about this cable is the fact the cap bridge had a very wide null. All the other cables had a very sharp null.

** = This cable has a clear covering, excellent braid, and is very flexable. It is about the same size as RG-59. However, this cable has 24 ct gold plated connectors. Since it is very close to the good 'ole RG-62, this is probably what I'll use for all the cables. I have some gold RCA connectors to install as well. Gonna use minimal cable length and align the R-4B/T-4XB twins with this pick.

Gotta love the 'bling'.........

FWIW

ron
N4UE

-----Original Message-----
From: Garey Barrell <k4oah at mindspring.com>
To: bonddaleena <bonddaleena at aol.com>
Sent: Sat, Jun 7, 2014 5:47 pm
Subject: Re: [Boatanchors] Drake cable question

Ron -

This is from the Archives....   The Belden 8421 is the best choice, as it is 
about the same size 
and flexibility as the other cables.  MUCH nicer to deal with than RG-62.

 >>>>>>>>>>>>>>>>>>>>>>

All original cables were 38" long tip-to-tip.

The INJ, (and CAR OSC in the C-Line,) cables used a foam inner dielectric and 
phono connectors 
with a white insulation.  This cable measures 60 pF total capacity.

All other cables used the standard for the day clear polyethelene inner 
dielectric and phenolic 
(brown) insulated phono connectors and measure ~100 pF.

Original Drake INJ and CAR OSC Cables = 19 pF/ft = .160" o.d. (foam poly)

RG-62 = 93R = 13.5 pF/ft = 0.240" o.d.
RG-59 = 75R = 14.8 pF/ft = 0.242" o.d.
RG-6 = 75R = 16.2 pF/ft = 0.270" o.d.
RG-174= 50R = 30.8 pF/ft = 0.110" o.d.
Mic Cable (Belden 8410) = Hi-Z = 33 pf/ft = 0.160" o.d. (foam poly)
Mic Cable (Belden 8421) = Hi-Z = 16 pf/ft = 0.180" o.d. (foam poly)
R/S Audio Patch Cable = 28 pF/ft = 0.165" o.d. (poly)

The best choice is the Belden 8421 Audio cable from their "Brilliance" line.  It 
looks just like 
the other cables, and is very flexible.  The RG-62 is OK, but it is 50% larger 
and far less 
flexible. RG-62 is also prone to shorting if bent over too small a radius, and 
is susceptible to 
heat damage when soldering connectors.  The best "feature" of RG-62 is
that it is often FREE, since there have been many miles of it pulled out of old 
computer 
networks. Belden 8421 is available by the foot from ACK Electronics in Atlanta.  
Other 
distributors have it as well, although many require purchase of a full spool. 
N7IOH, another 
list member, had some at one time that he was selling by the foot.

The only pertinent factor is the total capacity.  Impedance and "loss" are not 
important.

Any  _reasonably low capacity_  coax will work if the units are cabled together 
for the 
adjustment of the INJ trimmers.

The cable type ONLY affects the LEVEL of the PreMix signal, (5.645 MHz ABOVE the 

transmit/receive frequency,) and a small DC control voltage between the two.  If 
the shunt 
capacity is too high, insufficient LO level for the first mixer will reduce the 
sensitivity of 
the receiver and the output power of the transmitter.

Some of the "commercial" cable mfrs use RG-59A, but it's a little larger and 
also prone to 
shorting if bent over too tight a radius.

The ANT lead to the receiver is too short to matter, but you want good shield 
integrity, which 
usually eliminates R/S cables.

The best connectors I've found are the Switchcraft 3502 plugs, available from 
just about anyone, 
Digikey, Mouser, Allied, Newark and just about any reputable parts place.

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:
> Thanks to all who have responded. I'm gonna do a simple experiment....
> I have several lab quality cap meters/bridges. One is traceable to NIST 
standards.
> When I finally find my RG-62, I am going to measure the capacity of it and 
every other coaxial cable I can get my paws on.
> I think a 3 foot sample will be OK.
> Comments??
>
> ron
> N4UE
>
>   
>
>   
>
>   
>
> -----Original Message-----
> From: RAY FRIESS <rayfrijr at msn.com>
> To: Richard Knoppow <1oldlens1 at ix.netcom.com>; bonddaleena 
<bonddaleena at aol.com>; boatanchors <boatanchors at mailman.qth.net>
> Sent: Fri, Jun 6, 2014 8:02 pm
> Subject: RE: [Boatanchors] Drake cable question
>
>
>
> You are probably thinking of the Heathkit rigs.  Heath did recommend RG 62 for 
some of the connections between the sb 300 and 400.
>
>
>
>> Date: Fri, 6 Jun 2014 16:28:17 -0700
>> From: 1oldlens1 at ix.netcom.com
>> To: bonddaleena at aol.com; boatanchors at mailman.qth.net
>> Subject: Re: [Boatanchors] Drake cable question
>>
>>
>>
>>
>> -----Original Message-----
>>> From: Ron Bussiere via Boatanchors <boatanchors at mailman.qth.net>
>>> Sent: Jun 6, 2014 3:43 PM
>>> To: boatanchors at mailman.qth.net
>>> Subject: [Boatanchors] Drake cable question
>>>
>>> I finally found a 'rough' but complete T-4XB transmitter to go with my 
beloved R-4Bs.
>>> I have a lot of Drakes and the CDs, etc.
>>>
>>> Just wondering about the cables to connect the xmitter and rec. I know that 
RG-62 is 'recommended', and I actually may have some, In fact, I'm sure I do.
>>> However, just wondering why that 93 ohm cable was picked. Was it a matter of 
capacitance/foot, loss, resonance, what?
>>> That was a LONG time ago, and I have lots of the new low-loss RG-6, RG-59, 
RG-58. For such a small length, I'm wondering how much difference it makes on 
HF....
>>>
>>> Just an old timer trying to learn.........
>>>
>>> ron
>>> N4UE
>>      I double checked the handbook for both RX and TX and see nothing about 
recommended cable.  I use good quality hi-fi cables on my twins and they seem to 
work fine.  I have some memory that the injection cable should have relatively 
low capacitance but have not had any trouble the plain hi-fi hook up cables.  I 
am not sure if Garey Barrell, the maven from the Drake list monitors this list 
but if so I will defer to his opinion on this.
>>
>>
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