I left your message on this, don't normally do that but I think it is
important for context.
1. If the feed point impedance at your antenna is equal to the
characteristic impedance of your coax *at any given frequency,* then the
SWR you measure at the rig will be nominally 1:1. Note that not all SWR
measuring instruments are created equal.
2. Measuring the feed point impedance at an antenna is usually somewhat
hard ... up in the air, maybe not accessible ... you probably get the idea.
3. Measuring the SWR at the accessible bottom of the tower [I'm
assuming that's where you're measuring it], and finding it to be
anything other than 1:1 means that the line is not matched to the
antenna impedance, and begins acting as an RF transformer.
4. The SWR you will see in the shack, and remember that all SWR
indicators are not created equal, will be whatever results in the
impedance transformation along the length of the coax from the tower to
the shack.
5. A Time Domain Reflectometer will help clarify this for you if you
know how to use one. Sadly, they're very expensive and hard to
interpret if you've never used one. Check around among your friends but
don't hold your breath.
Bottom line, you can prune or un-prune your antenna [if it's wire] a
little, and you can adjust the length of the coax transformer to the
shack to get acceptable SWR at the rig.
Or, if your K3 accepts the SWR, ignore it. Honestly Mark, you'll never
know the difference while operating. There's also the KAT3, your SWR's
are easily within it's range.
There was a time, in my lifetime, when "Standing Wave Ratio" was NOT an
amateur radio term. You "loaded the antenna" and called CQ. Today's
radios are significantly more particular to SWR, but if it works, it works.
73,
Fred K6DGW
- Northern California Contest Club
- CU in the 2014 Cal QSO Party 4-5 Oct 2014
- www.cqp.org
On 9/2/2014 5:06 PM, [email protected] wrote:
Good Evening, This is Mark Griffin, KB3Z and I have some questions
regarding the SWR readings I get at my tower versus what I get on my
K3. I will give the SWR readings that I got at my tower for a 40
meter rotatable dipole at 55 feet.
Tower:
7000 2.2 7025 1.8 7050 1.5 7075 1.3 7100 1.0 7125 1.1 7150
1.3 7175 1.6 7200 2.0 7225 2.2
K3 Readings:
7000 3.5
7025 3.2
7050 2.9
7075 2.6
7100 2.4
7125 2.3
7150 2.4
7175 2.5
7200 2.6 7225 2.9
What would cause such a big difference. The cable run from my antenna
switch on the tower to my K3 is only an additional 75 feet. I am
using RG-213 cable. Is there anyway that I can test the SWR reading
that my K3 is giving me?
Mark Griffin, KB3Z
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
