[Boatanchors] Should dummy load oil ever need to be changed?

[J. Forster]

Gene,

I think not to first order, as long as the coax is fairly long (in
wavelengths at the frequency of operation). I suspect it's quite a long
piece of RG-8 to make a useful dummy load at a few MHz.

I suspect that the exact lengtn will make a difference if examined with a
VNA, but the longer the cable (in wavelengths) the smaller the effect.

Years ago, I was trying to test an antenna at 2.2 GHz. The only source
available was an AILtech Power Oscillator. 100' of RG-58 knocked the
output way down. Note that 100' is a lot of wavelengths of 2.2 GHz.

As to oil in Cantennas leaking, my experience has been that the cans do
rust if in a place of modest humidity, where the temperature cycles often,
causing the thing to "breathe". Water vapor consenses, as in a gas tank,
and reacts with some oils over time. The reaction products 'eat' the can.
I would expect far fewer failures in AZ than in ME, for example.

Best,

-John

================



> Does the length need to be something specific based on the frequency
> you're' using?
>
>
> 73 Eugene W2HX
>
>
> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net
> [mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of Ray
> Sent: Saturday, August 25, 2012 1:14 PM
> To: boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] Should dummy load oil ever need to be changed?
>
> A useful dummy note note which may interest some:
>
> A piece of coaxial cable open or shorted at the far end with a loss rating
> of about 15 db or more at your frequency of interest, will provide a very
> nice dummy load.  It will provide a return loss of about
> 30 db (-15db forward loss and -15db reverse loss) .
>
> If you use a piece of cable rated at about 20 db of loss at your frequency
> of interest, you will have a near laboratory quality dummy load (40db RL).
>
> Make sure the cable is rated sufficiently for the power level you are
> going to use it with.
> Ray, W4BYG
>
>
> On 8/25/2012 12:09 PM, Bill Cromwell wrote:
>> On Sat, 2012-08-25 at 11:45 -0400, Wayne D Anderson wrote:
>>> Gentlemen
>>>
>>> It seems to me that in a hobby that found the use of a lightbulb as an
>>> acceptable  load, the Cantenna looks like a pretty good alternative.
>>>
>>> 73
>>> K7WDA
>> Hi,
>>
>> There are some radios that went to war with a light bulb for tuneup.
>>
>> 73,
>>
>> Bill  KU8H
>>
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