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Author Topic: Tuning Multi Band Antenna  (Read 1360 times)
KD2CJJ
Member

Posts: 369




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« on: April 17, 2013, 01:14:23 PM »

Elmers,

What is best practice in general when tuning a multi band antenna that is trap OR top loaded.  Start with 10m  and tune each band to the lowest band like 20m OR visa versa start at the lowest band like 20m  and tune for each band up to 10m as an example?

thanks

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73

Mike
KD2CJJ
N6AJR
Member

Posts: 9921




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« Reply #1 on: April 17, 2013, 01:28:05 PM »

what kind of tune do you mean?  if you are tuning the physical antenna for length etc, I say start with the lower freqs (20 m) and tune up ( 10 meters). for the least interaction.   if you are tuning with a tuner  for a particular frequency, then it does not matter.
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KD2CJJ
Member

Posts: 369




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« Reply #2 on: April 17, 2013, 01:43:15 PM »

Yes physically tune the antenna for least interaction...

Thanks

what kind of tune do you mean?  if you are tuning the physical antenna for length etc, I say start with the lower freqs (20 m) and tune up ( 10 meters). for the least interaction.   if you are tuning with a tuner  for a particular frequency, then it does not matter.
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73

Mike
KD2CJJ
K1WJ
Member

Posts: 460




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« Reply #3 on: April 17, 2013, 02:06:56 PM »

Start at the bottom of the antenna - 10m then 15m then 20m then 40m. Go to DX Engineering site & down load the Hustler 4BTV install instructions - that is how you do it, your dimensions will be different but basic principles still apply. 73 K1WJ David
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KD2CJJ
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Posts: 369




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« Reply #4 on: April 17, 2013, 02:16:22 PM »

As you can see why I asked - I am getting conflicting recommendations.  This is a rigid dipole - some say start at 10 meters and work your way out to 20.. other say start at 20 outer, and work your way in 10m.

Which is it?
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73

Mike
KD2CJJ
K1WJ
Member

Posts: 460




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« Reply #5 on: April 17, 2013, 03:06:03 PM »

A rigid trap dipole is the same as the Hustler 4BTV vertical
Because the 1st section of tube & trap from feed point is 10m.
The adjustment of 10m will effect the adjustment of tubes & traps for the lower bands beacuse they are additive. Look up the cushcraft D3 install instructions = a trap dipole.
Again the Hustler 4btv vertical install applies the same principals.
Just do it..........73 K1WJ David
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WB6BYU
Member

Posts: 13486




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« Reply #6 on: April 17, 2013, 08:41:02 PM »

If you have a traditional trap dipole, say, for 10 / 15 / 20m, the 10m length
adjustment affects all three bands, the 15m affects 15m and 20m, and the tip
length affects only 20m.  If you tune 20m first, then when you adjust either
of the other bands it will throw the original tuning off.  That's why, in this case,
you start with 10m first, then 15m, then 20m.

If you have parallel dipoles on a common feedpoint, then you'd adjust the
longest wire first, because the short wires for the higher frequencies have
less effect on the low frequencies than the other way around.


In both cases you start with the adjustment that will impact the most other
bands, but which adjustment that is depends on the specific antenna
design.
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KB5UBI
Member

Posts: 97




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« Reply #7 on: April 17, 2013, 08:54:32 PM »

If you have a traditional trap dipole, say, for 10 / 15 / 20m, the 10m length
adjustment affects all three bands, the 15m affects 15m and 20m, and the tip
length affects only 20m.  If you tune 20m first, then when you adjust either
of the other bands it will throw the original tuning off.  That's why, in this case,
you start with 10m first, then 15m, then 20m.

If you have parallel dipoles on a common feedpoint, then you'd adjust the
longest wire first, because the short wires for the higher frequencies have
less effect on the low frequencies than the other way around.


In both cases you start with the adjustment that will impact the most other
bands, but which adjustment that is depends on the specific antenna
design.

KD2CJJ,

You didn't mention what kind of antenna you have. I am assuming you have a trap antenna and not an antenna with resonating coils such as a Butternut HF6V which may require starting with the lower frequency bands and working your way up.

KB5UBI
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KD2CJJ
Member

Posts: 369




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« Reply #8 on: April 18, 2013, 06:34:26 AM »

I have a TGM MQ26 mini beam.  It is top loaded with Capacitance hats for each band... The manufacturer says to tune from 20m (outer ring of spokes) up to 10m (the inner ring of spokes).  It didnt make much sense to me as it seems to me each higher band loads the lower band - so I was trying to get more of a general understanding how to properly tune a multi band antenna.  I guess I should have asked the difference between tuning a trap based antenna vs a capacitance loaded antenna.

Here is the antenna -
http://www.tgmcom.com/index.php?option=com_content&view=article&id=31:model-mq-26&catid=42:5-bands-2017151210-meters&Itemid=63

If you have a traditional trap dipole, say, for 10 / 15 / 20m, the 10m length
adjustment affects all three bands, the 15m affects 15m and 20m, and the tip
length affects only 20m.  If you tune 20m first, then when you adjust either
of the other bands it will throw the original tuning off.  That's why, in this case,
you start with 10m first, then 15m, then 20m.

If you have parallel dipoles on a common feedpoint, then you'd adjust the
longest wire first, because the short wires for the higher frequencies have
less effect on the low frequencies than the other way around.


In both cases you start with the adjustment that will impact the most other
bands, but which adjustment that is depends on the specific antenna
design.

KD2CJJ,

You didn't mention what kind of antenna you have. I am assuming you have a trap antenna and not an antenna with resonating coils such as a Butternut HF6V which may require starting with the lower frequency bands and working your way up.

KB5UBI
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73

Mike
KD2CJJ
WB6BYU
Member

Posts: 13486




Ignore
« Reply #9 on: April 18, 2013, 09:48:24 AM »

What adjustment are you making to tune the antenna?  The length of the
element between traps, the size of the capacity hat for each band, or
something else?

If you are adjusting the capacity hat, there might be enough interaction
among them to require adjustment at 20m first.  With 5 traps in such a
short space, each with loading capacitance that will couple to the
surrounding capacitors, there likely will be a lot of interaction and following
the manufacturer's instructions is the best approach (at least until it is
shown not to work.)
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KD2CJJ
Member

Posts: 369




Ignore
« Reply #10 on: April 18, 2013, 12:59:16 PM »

For each of the bands on the driven element there are two (one on each leg) tuning spokes where by you lengthen or shorten.    I have yet to tune the antenna - hopefully this weekend.

thanks

What adjustment are you making to tune the antenna?  The length of the
element between traps, the size of the capacity hat for each band, or
something else?

If you are adjusting the capacity hat, there might be enough interaction
among them to require adjustment at 20m first.  With 5 traps in such a
short space, each with loading capacitance that will couple to the
surrounding capacitors, there likely will be a lot of interaction and following
the manufacturer's instructions is the best approach (at least until it is
shown not to work.)
Logged

73

Mike
KD2CJJ
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