[Antennas] J-Pole

Thu Sep 30 18:46:34 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.
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
>>> >> >
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