Steve asked me to post the following message for him.
(he is having trouble getting his post to go through)
-Rick
--------
I say it's not 50:50 :)
The impedance will "rotate around" a Smith Chart centred on the open wire
characteristic impedance - typically 600 Ohms. So, for example, a 15:1 SWR
on the open wire will swing the impedance at the balun between 9,000 Ohms
and 40 Ohms; for the majority of lengths the impedance would be above 50
Ohms.
Only if it were 50 Ohm line would there be a 50:50 chance of it being above
or below 50 Ohms.
Steve G3TXQ
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Carl
Moreschi
Sent: Sunday, November 10, 2013 3:26 AM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Ten Tec 238 coupler and 160 meters
If you use coax for an 80 meter dipole and run it on 40 meters with coax,
the loss will be very high. That's because the additional loss from a high
SWR (around 100 to 1 in this case) is huge.
If you run open wire line on an 80 meter dipole and use it on 40 meters, the
additional loss is not that bad. That's why we use open wire line on a
single band dipole to use it on more than one band.
Carl Moreschi N4PY
58 Hogwood Rd
Louisburg, NC 27549
www.n4py.com
On 11/9/2013 6:49 PM, Ken Brown wrote:
>
>> That's a new one on me. How could loss be less with high SWR on a
>> short length of coax? It makes no sense.
>>
> The loss in coax at HF frequencies is not that high, and the
> additional loss due to high SWR is also not that high. (At least
> compared to what happens at VHF) For HF systems keeping SWR low on
> coax is still a good idea, but it is more to reduce the possibility of
> HV arc over than to minimize the loss. (A matter of opinion no doubt,
> but if you work out the numbers you may have the same opinion) If the
> added line is short and makes it easier for the tuner to match, the
> additional loss in the coax is likely to be less than the reduced loss
> in the tuner when it sees an easier to match impedance.
>
> DE N6KB
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>
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