Anyone know how many ohms I should be measuring at the end of a 25ft
coax cable connected to a 60ft Delta antenna? Right at the 529
connection at the connection end of the antenna the resistance is
infinite. But at the bottom of 25ft of coax feeder the resistance is
about 5meg ohms. Does that sound right? Also, if I measure the coax
at the antenna (not connected to the antenna (just going 25ft to
radio) it measures infinite. Don't understand it. Does it have
anything to do with my ground maybe?

Anyone know how many ohms I should be measuring at the end of a 25ft
coax cable connected to a 60ft Delta antenna?

Near zero. As I understand a Delta, or Delta Loop antenna, the DC resistance
should be zero ohms. The Delta is a closed loop. Down at the end of your coax
the DC resistance will be zero from center conductor to shield. Probably need
to disconnect the the coax from the antenna and check them seperately to insure
the coax is not shorted, and the antenna reads a short.

Right at the 529 connection at the connection end of the antenna the
resistance is infinite.
Not sure about a 529 connection, but if you take the ohm readings with the
antenna disconnected from the coax, you should find the problem.


73 Gary N4AST

On 07 Jul 2004 23:15:38 GMT, (JGBOYLES) wrote:

Anyone know how many ohms I should be measuring at the end of a 25ft
coax cable connected to a 60ft Delta antenna?

Near zero. As I understand a Delta, or Delta Loop antenna, the DC resistance
should be zero ohms. The Delta is a closed loop. Down at the end of your coax
the DC resistance will be zero from center conductor to shield. Probably need
to disconnect the the coax from the antenna and check them seperately to insure
the coax is not shorted, and the antenna reads a short.

Right at the 529 connection at the connection end of the antenna the
resistance is infinite.
Not sure about a 529 connection, but if you take the ohm readings with the
antenna disconnected from the coax, you should find the problem.


73 Gary N4AST

Appreciate the help but it's not a closed loop. At least I don't
think so. There are two antenna lines - ones 60ft and the other 16ft.
They are connected to the 529 center post. The ground lead (30ft) is
connected to the outer part of the 529. I'm pretty sure it's right
that there is infinite ohms there because they are not physically
touching in any way. I'm confused because simply adding 25ft of coax
causes a 2.5meg ohm reading. In essence I'm still across the 529 just
25ft further away. So nothing should change.

Tainted wrote:
Anyone know how many ohms I should be measuring at the end of a 25ft
coax cable connected to a 60ft Delta antenna?

DC? or RF?



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On Wed, 07 Jul 2004 22:45:26 -0500, Cecil Moore
wrote:

Tainted wrote:
Anyone know how many ohms I should be measuring at the end of a 25ft
coax cable connected to a 60ft Delta antenna?

DC? or RF?



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DC

Tainted wrote:
Cecil Moore wrote:

Tainted wrote:
Anyone know how many ohms I should be measuring at the end of a 25ft
coax cable connected to a 60ft Delta antenna?

DC? or RF?

DC

You will be reading the leakage resistance. What kind of coax?
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:

Tainted wrote:
Cecil Moore wrote:

Tainted wrote:
Anyone know how many ohms I should be measuring at the end of a 25ft
coax cable connected to a 60ft Delta antenna?

DC? or RF?

DC

You will be reading the leakage resistance. What kind of coax?

Isn't he talking about a loop antenna??

jk

Appreciate the help but it's not a closed loop. At least I don't
think so. There are two antenna lines - ones 60ft and the other 16ft.
They are connected to the 529 center post. The ground lead (30ft) is
connected to the outer part of the 529. I'm pretty sure it's right
that there is infinite ohms there because they are not physically
touching in any way. I'm confused because simply adding 25ft of coax
causes a 2.5meg ohm reading. In essence I'm still across the 529 just
25ft further away. So nothing should change.

You might (as someone else suggested) be reading some leakage
resistance from your coax. 2.5 megs seems a low reading for coax in
good condition... if it's the coax, you might have gotten some water
or other contamination into the connectors, or into the coax itself.

Depending on how you're holding your meter probes when you do the
measurement, you might be reading your skin resistance by accident.
Make sure your skin isn't touching the metal parts of either probe.

Depending on the meter you are using, you might not be reading just
the resistance. Since you're doing a measurement on a coax and
antenna, the antenna is likely to be picking up some amount of RF from
nearby transmitters. There would probably be some differential-mode
RF within the coax (from in-band reception by the antenna), and likely
some common-mode coming down the outside of the coax. Your meter's
circuitry might be acting as a pathway to complete the RF circuit -
this would allow some amount of RF current to flow through the
metering circuitry (in addition to the DC current which results from
the resistance-measuring voltage the meter is presenting), and the
meter's reading might be the result of this small RF current flow.

As an experiment, try bypassing the bottom end of the coax... create
an RF short circuit across the PL-259 with a .1 uF capacitor. See if
this makes the apparent resistance at this point go up... if so, the
resistance reading was probably due to stray RF getting into the meter.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Jim Kelley wrote:

Cecil Moore wrote:
You will be reading the leakage resistance. What kind of coax?

Isn't he talking about a loop antenna??

Here's a quote by the author from a few postings ago.

Appreciate the help but it's not a closed loop.

So it must be an open loop.
--
73, Cecil http://www.qsl.net/w5dxp



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