[GreenKeys] Coax type for simple vertical

[Bob kb8tq]

Hi

The impedance of a quarter wave vertical over a perfect zero resistance / infinite extent ground is 
half the 75 ohms of a dipole far from ground. Whatever ground resistance you have adds to the 37 ohms.
It is *rare* to get below 10 ohms for the ground side of the antenna…..

If you have a vertical that is something other than N x 1/4 wave, you will need a matching network to
take out the reactance. The design of that network will impact the impedance presented to the feed line.
It could be quite low, quite high, or 50 ohms ….

Bob

> On Oct 13, 2017, at 10:59 PM, Ralph Irish <w8roi at wowway.com> wrote:
> 
> Tony, et al
> 
> It seems to me that the 'natural impedance' of most quarter wave verticals is below 50 ohms.  I
> remember reading in one of the ham magazines that putting a "Tee" fitting on the back of a mobile
> rig and feeding the antenna with  TWO  pieces of RG-59 coax (resulting in a 37.5 ohm impedance)
> seemed to do quite well in many mobile installations.  I tried this once with a borrowed SWAN-240
> that I hurriedly installed in my Ford Mustang convertible.  (1966?)  
> 
> I was planning a trip to Milwaukee to attend the wedding of a cousin.  I ran the two pieces of coax
> in the 'tunnels' on either side of the car, under the plates that sat on top of the 'tunnels'** and
> into the trunk.  I used a clamp type mount on the front edge of the trunk.  The antenna was a 40M
> Mark Mobile 'heliwhip' antenna, already tuned for the middle of 40M phone.  I had great QSOs all
> the way to and from Milwaukee, and really impressed a brother of the bride, when I showed him the
> rig and made a handful of contacts from his driveway.  Didn't plant seeds for a new ham, but he 
> thought that the concept of talking to people all over was 'pretty neat'.
> 
> Ralph - W8ROI
> 
> **   The 'tunnels' were under the bottom of the closed door.  There was a decorative and 
>      functional cover which enclosed some wiring from under the hood to the tail lights, turn
>      signals, etc.  The coax was pushed 'parallel' to the small bundle of car wires and followed
>      the same path into the trunk.  One of the easiest mobile antenna install jobs I can remember.
> 
> ROI
> 
> - - - - - - - -
> 
> On Oct 13, 2017, at 8:45 PM, tony.podrasky wrote:
> 
>> GA OMs;
>> 
>> I'm going to try using a 28' telescoping fiberglass pole
>> with a wire taped to the top, running down the length
>> of the pole, to an SO-293. The pole will be attached
>> to my upstairs balcony - so I can take it down when I'm
>> done (CC&R stuff).
>> 
>> Should I be using 52 or 75 Ohm coax to feed it?
>> 
>> UE,
>> K2EAA - TONY
>> NNNN
>> ZCZC
>> 
>> -- 
>> Sure, we can do it - just select any TWO:
>> +---------------------------------------+
>> |    GOOD    |    FAST    |    CHEAP    |
>> +---------------------------------------+
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