Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Old style antenna match questions  (Read 823 times)
KD5NDQ
Member

Posts: 21




Ignore
« on: March 18, 2012, 06:57:12 AM »

Bear with me please to being new on the air and this equipment... I purchased a Dentron RT-3000 antenna match. My rig is a Kenwood TS-530S and a 1/2 wave 40m dipole that is in the air about 40' up and fed with 100' of RG-8X coax.

I bought the Dentron without seeing it first and now that I have it (and having repaired the roller inductor - thank you JB WELD!) I realize it's not like currently made tuners with the "cross needle" type meter. The panel has a single needle meter that says "RF Reflected Power" with 2 scales - one that goes to 200 and one to 2000.
http://opalko.smugmug.com/Other/Tuner/i-bPKCqLn/0/O/photo-5.jpg

The 1 page instruction manual that comes with it describes operation of the tuner as follows:
Quote
Operation:
1. Set transmitter matching and antenna matching controls to 50.
2. Listen on receiver for maximum band noise while turning roller inductor for maximum noise.
Caution: Do not turn counter below 00.00 or exceed 36.00 or serious damage may result to the roller inductor.
3.Appy enough power to the system to get a reading on the meter in the reflected position
4. Rotate the roller inductor for a drop in reflected power reading.
5. Adjust "transmitter matching" and "antenna matching" controls for a minimum reading of reflected power.

Now for my questions!
1) What is "maximum band noise"? Static? I gave up on trying to tell a difference on this step and went to step 3 instead.

2) Being young and naive, I tuned the TS-530S to the 20m band I wanted to work (remember I have a 40m dipole). I followed steps 4 & 5 and got the minimum reading of reflected power close to 0. I made 4 contacts with 5x9 signal reports shortly thereafter - 1 DX and 3 stateside.
Then I made the mistake of reading more on these forums... From what I read and understand, there is no way I should be able to operate on 20m with a 40m dipole, even with an antenna match... so why did it work? Did I hurt the transceiver in the process?

3) Should I buy a separate SWR meter to use with this tuner? If not, what is the advantage of having one?

Thanks,
Robert Opalko
KD5NDQ
Logged
K9YLI
Member

Posts: 848




Ignore
« Reply #1 on: March 18, 2012, 07:45:16 AM »

The noise  aka  band noise is the background  static   hisss etc where no signal is present.
In between  stations you can hear..

For  20 meters  the roller on the inductor  should be  about  1/4 of the way frm the non grounded  end.  (usually the front or   low  number on the counter)
The  noise change should be  quite noticable, but  possibiliy  rather sharp. ( only a few turns
counter numbers..so  crank slowly.)
Also I think  a  530  has  tube  finals  and therefore  a  PI net  output..  think   drive   tune and load  controls.
To use  tuner  I tihnk  you need to  tune the radio into a dummy load to set it up for  a given frequency..   then  leave the radio  contrls  alone while you  adjust the tuner..

 Yes.. put the  swr  functin on  calibrate.  apply a little power and  adjut meter control for full scale.     then switch to swr..   no apply  same power and  adjust  coil for  minimum.
then  antenna control for minimum, and  tramsmitter control for minimum.
tweak  all three for  final minumum..hopefully  below  1.5   

a 40 meter antenna is  just a fulll wave antenna on  20 meters.. impedance  of a full wave is  different  but the tuner  may  well cover it.. not every thing you read on the internet  is   gospel truth
Logged
N4CR
Member

Posts: 1650




Ignore
« Reply #2 on: March 18, 2012, 08:26:17 AM »

Tuning a 40 meter antenna for 20 meters and making contacts is only proof that a compromised antenna can still make contacts when propagation supports it.

Because a full wave antenna is high impedance at the feed point it sets your system up for creating a lot of power loss (as heat) in your feed line. The more mismatch, the more loss and feeding a full wave antenna at the center with low impedance feed line is pretty much a worst case scenario.

Assuming you were actually able to tune this antenna in the manner you describe there is no reason to think you damaged anything. The worst stress on your antenna system would be that trying to tune a huge mismatch puts a lot of stress on the tuner and might cause arcing across the internal components.

Take a look at a couple of antennas to alleviate this issue...

First, a fan dipole is a method of adding other resonant or near resonant elements to your existing antenna to add more bands.

Second, a ladder line fed doublet with it's wires a little too long for the highest band and a balanced tuner to feed it with.

Either of these will let you tune up with less power lost in the feed line. The entire point of this exercise should be to deliver as much power as possible to the feed point of the antenna.
Logged

73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
WB6BYU
Member

Posts: 13010




Ignore
« Reply #3 on: March 18, 2012, 09:28:11 AM »

Quote from: KD5NDQ

...The panel has a single needle meter that says "RF Reflected Power" with 2 scales - one that goes to 200 and one to 2000.


So there are two ranges for FORWARD power and one for reflected power.


Quote

The 1 page instruction manual that comes with it describes operation of the tuner as follows:
Quote from: the manual
Operation:
1. Set transmitter matching and antenna matching controls to 50.
2. Listen on receiver for maximum band noise while turning roller inductor for maximum noise.
Caution: Do not turn counter below 00.00 or exceed 36.00 or serious damage may result to the roller inductor.
3.Appy enough power to the system to get a reading on the meter in the reflected position
4. Rotate the roller inductor for a drop in reflected power reading.
5. Adjust "transmitter matching" and "antenna matching" controls for a minimum reading of reflected power.

Now for my questions!
1) What is "maximum band noise"? Static? I gave up on trying to tell a difference on this step and went to step 3 instead.


The general back ground noise - could be signals or whatever else you hear in the receiver.
Sometimes this has a sharp peak, sometimes it doesn't.  With some antennas I can pretty
much tune my tuner using this alone.  But it may be more abrupt tuning a capacitor than
with a roller inductor, which requires more time to move from one end of the range to the
other.

You don't have to do this step - it just helps you get close to the final setting.


Quote

2) ...Then I made the mistake of reading more on these forums... From what I read and understand, there is no way I should be able to operate on 20m with a 40m dipole, even with an antenna match... so why did it work? Did I hurt the transceiver in the process?



You didn't hurt the transceiver.  And, yes, it does work, just not very efficiently.
There are a lot of details to the answers in these forums.  Sometimes hams remember
to state the conditions and assumptions, sometimes they don't.  Rarely is there
a clear, unambiguous answer "yes it works" or "no it doesn't", rather there is a range
of how well it works, and whether there is a better option.

In the case of using a 40m dipole on 20m, I've done that, too.  Or maybe it was working
40m DX on an 80m dipole running QRP.  It certainly wasn't optimum, but it made contacts.

In your case, we can guess that the impedance of the 40m dipole used on 20m is around
2000 ohms (SWR = 40 : 1).  If we plug that into VK1OD's transmission line loss calculator
(http://www.vk1od.net/calc/tl/tllc.php) for 100' of RG-8X (Belden 9258) it predicts a
loss of 7.9dB, so about 16% of your power reaches the antenna.  If you are running 100W,
about 16 watts get radiated.

That's not very good for efficiency.  With a proper match you'd have 78 watts radiated
instead (due to the 1dB loss in the coax when matched.)  But I make lots of contacts
running 5 watts, and you're still stronger than that.  With good conditions it is still
enough to work around the world - but you wouldn't need the conditions to be quite
as good if you didn't have the the extra feedline loss.


Quote

3) Should I buy a separate SWR meter to use with this tuner? If not, what is the advantage of having one?



As long a the built-in meter is adequate to tune the antenna, you don't need one.
Sometimes it is useful to measure the SWR without the tuner in the line - for example,
you should be able to run the 40m dipole straight into the rig on 40m without any tuner.
In that case a separate SWR meter may be useful.
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!