[Antennas] J-Pole

Fri Oct 1 05:01:19 EDT 2004

> John,
> Are you suggesting that THREE baluns would make the measurement possible?
>> A- --------------------
> N |4:1 balun|-swr meter-|1:4 balun|[open wire feedline]|4:1 balun|-coax
> T- --------------------
>> Hope that diagram looks ok...
> Antenna connected to 4:1 balun connected to coax with 50-ohm swr meter 
> connected to 1:4 balun connected to open-wire feedline connected to 4:1 
> balun connected to coax ... to rf source.
>> I can't see ANY other way of measuring feedline LOSS AT THE ANTENNA.

 No.. I'm saying coax from rig to matching unit, to open wire line, to 
matching unit, to coax to antenna.. The matching unit is not neccessarily a 
4:1 balun..
John EI7BA..
> Don
> N8DE
>> John Tait wrote:
>>>> Subject: Re: [Antennas] J-Pole
>>>>>>> John...
>>>>>> We knew all of that... But anything other than coax is impractical from 
>>> a
>>> measurement standpoint...
>>>>>> I don't see why??? you need to measure power in from the TX, and the 
>> power to the antenna at the other.. The difference between the two tells 
>> us the efficiency of the line.
>>>>> How much test gear exists that will provide
>>> reasonable accuracy with ladder-line..? With the exception of ancient
>>> LECHER WIRES, I can't think of any...(smile)
>>>>>> The same gear that you use for your 50 ohm coax will suffice. If you're 
>> feeding an antenna that was built to be fed by coax, you're coming from a 
>> 50 Ohm source to a 50 Ohm load via two transformers, ATUs or WHY, with 
>> open wire line between them. You could measure efficiency in the same way 
>> as you would a 4:1 balun ..i.e.two baluns back to back, measure power in 
>> and power out .
>> e.g 100W in.. 80W out. 20W lost, so 10W lost in each balun so the baluns 
>> are 90% efficient. (at that frequency). Same procedure with your open 
>> wire line.
>>>> 73
>> John EI7BA
>>>>>>>>>> 73, Larry - W1GOR
>>>>>>>>> ----- Original Message -----
>>>>>>> From: "John Tait" <bravo at iol.ie>
>>>>>> To: "Joe" <nss at mwt.net>; "W1GOR" <W1GOR at maine.rr.com>
>>> Cc: <antennas at mailman.qth.net>; "Durwydd MacTara" <durwydd at hotmail.com>
>>> Sent: Wednesday, September 29, 2004 1:18 PM
>>> Subject: Re: [Antennas] J-Pole
>>>>>>>>>> No.. I don't think he's kidding.. The whole point of open wire feeeder 
>>>> is
>>>> that it has very low loss. It is the most efficient feeder type that's
>>>> available to us. Line loss increases with frequency, with SWR,and with
>>>>>> line
>>>>>>> length, so VHF/UHF antenna system have the most to gain by using open 
>>>> wire
>>>> line. Good quality "Ladderline" is a less efficient feeder than proper
>>>>>> open
>>>>>>> wire line, but has less loss than coax..'specially if SWR is high.
>>>> However.. coax is much simpler to deploy than open wire line, and 
>>>> good
>>>> quality hardline has acceptable losses so long as SWR is low, and 
>>>> lengths
>>>> reasonable. Most of us settle for that, and put up with the losses. We 
>>>> can
>>>> compensate for loss of transmitted power by using a linear amplifier, 
>>>> and
>>>> for RX loss with a good low noise mast head preamp.
>>>> 73
>>>> John EI7BA http://www.iol.ie/~bravo/
>>>>>>>>>>>> >
>>>> > W1GOR wrote:
>>>> >
>>>> >> Ladder-Line for VHF/UHF...? You've gotta be kidding..!
>>>> >>
>>>> >> 73, Larry - W1GOR
>>>> >>
>>>> >> ----- Original Message -----
>>>> >> From: "Durwydd MacTara" <durwydd at hotmail.com>
>>>> >> To: <Antennas at mailman.qth.net>
>>>> >> Sent: Tuesday, September 28, 2004 10:20 AM
>>>> >> Subject: [Antennas] J-Pole
>>>> >>
>>>> >> > I have a homebrew 2M/70CM J-pole 50 ft. in the air for use with
>>>> a 5W
>>>> >> > HT.
>>>> >> Am
>>>> >> > currently using RG-213 for feedline. i am wondering if it is worth
>>>>>> the
>>>>>>> >> > effort to switch the feed to ladder line, and if so how to do it?
>>>> >> >
>>>> >> > "Carpe` Diem!"
>>>> >> > Durwydd MacTara
>>>> >> >