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Author Topic: feeding HF Dipole  (Read 6049 times)
YONU
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Posts: 67




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« Reply #15 on: December 26, 2012, 08:10:19 AM »

Thanks I will give it a shot when this rain stops.

 As to the pcv last it is 30ft high from 3in down to 1.5in I had planned to use it as the center support I have had it standing for the last week and it is still up so I figure it should work OK as a center support
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N8CMQ
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Posts: 373




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« Reply #16 on: December 26, 2012, 09:59:29 AM »

Hey Reg, if money is a problem, then, whatever you can get working for now is ok.
As far as coax goes, RG-58 is ok for HF to 30 MHz without too much worry at
reasonable lengths and power.
If you can put down radials in a circle about 30 feet long, you could put up a
vertical and have much better operation.
By swapping out vertical elements, you could have a multi-band antenna as well.
Or get a trap vertical, then you don't have to swap anything.
Just another option to think about for your current setup.
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W5DXP
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Posts: 3613


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« Reply #17 on: December 26, 2012, 10:31:14 AM »

As to the pcv last it is 30ft high from 3in down to 1.5in ...

30ft is asking a lot from PVC pipe - I've had trouble with heights above 20ft. But the good news is you don't need standoffs if the support pole is PVC.
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
W5LZ
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Posts: 477




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« Reply #18 on: December 26, 2012, 11:02:59 AM »

Would your idea work?  It can, if you -have to- do it that way.  But then, that RG-58 will work at least as well and be much simpler to use, and you can bury the stuff.
I haven't had much luck using PVC as an antenna support, just too flimsy and the sun does affect it.  There's not much benefit to using a non-conductive 'mast', metal masts have worked just fine for a lot of years.  Sure, there's some affect but nothing that's all that noticeable.
 - Paul

(I honestly don't know of any ham that just has -one- antenna and has never changed it.)
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YONU
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Posts: 67




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« Reply #19 on: December 26, 2012, 11:45:02 AM »

well I was rumaging through my rolls of RG6 looking for a small bundle and have a piece of RG8 in the box with them so I am replacing the Twin feed with RG8  I will more than likely use the PVC atleast until I find a good price on a metal mast.  out of curiosity I don't have a tuner yet so what should the proper length me for 10m for each Leg if I did my math right I am figuring 12ft.
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WB6BYU
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Posts: 13335




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« Reply #20 on: December 26, 2012, 12:03:06 PM »

No reason not to use RG-6 all the way from the rig to the antenna if that is what
you have on hand.  It is lighter and has lower loss.


The standard formula for a half wave dipole is 468/F.  For 10m this would be
468/28.5 = 16.4' overall, or 8.2' each side of center.  I'd make it a bit longer
than that to give you some room for pruning.

I also recommend putting a pulley and halyard on your mast so it is easy to raise
and lower the dipole for adjustments - it might take a couple tries to get the
antenna tuned where you want it.
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YONU
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Posts: 67




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« Reply #21 on: December 26, 2012, 12:47:59 PM »

well I got it up and trimmed both Legs to 9ft however I am getting no reception that I can tell I actually think I used to small of wire on the legs I used 18GA as I had it laying around should I up the size  I am getting a SWR of 1:1.5 though if I am reading the meter with however the odd think is with the radio on 100w it is only indicating 20w output

Thanks,
Reg
KK4NJC
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WB6BYU
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Posts: 13335




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« Reply #22 on: December 26, 2012, 01:09:01 PM »

If you have an SWR of 1 : 1.5 then the problem is you are reading the meter upside down.
SWR is always defined as being the ratio of a larger number to one, so 1.5 : 1.

But if you have a 75 ohm dipole at end of some 75 ohm coax, and then measure
the SWR with a 50 ohm reference meter at the rig, it should show 1.5 : 1, and the
rig should work OK at that impedance.

However, if the rig doesn't put out much power, there may be some other problem
that is causing an incorrect indication.

What are you using to measure SWR?  Can you find the frequency at which the SWR
is lowest?  If you plot both the SWR and the output power at a few frequencies across
the 10m band, does that give you a sense of where it works best?

What rig are you using?  What mode are you using to measure the SWR?

Wire size doesn't make any difference in this case.  I often use #24 or smaller. 
I'd guess that 9' is still too long.  This is where it is often most convenient to have
a nearby ham come over and look at your installation - sometimes you find quirks
such as a poor ground connection on the coax, or a switch in the wrong position,
etc., that it is difficult for us to find over the internet.

And sometimes you can't hear anything on 10m because the band is dead: 
generally you'll hear the most signals between about noon and 4pm local time,
but it can be quiet for weeks (or months, or years) at a time.
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YONU
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Posts: 67




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« Reply #23 on: December 26, 2012, 01:20:23 PM »

ok the Rig is a YAESU FT-757GXII  the SWR meter is a jetstream 1.8-200mhz meter.  ok now for the very stupid question I don't have the rig hooked to a separate ground as I wasn't sure if it was nessesary as I am running it straight from a 12v Deep Cycle

and yes I know that 10m tends to be dead I just figured I would start there get it working then move to the other bands I am authorized for.
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WB6BYU
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Posts: 13335




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« Reply #24 on: December 26, 2012, 02:09:31 PM »

Quote from: YONU
ok the Rig is a YAESU FT-757GXII  the SWR meter is a jetstream 1.8-200mhz meter. 



That may give us some clues, anyway.

I think the Jetstream is a manual meter - that is, the sensitivity has to be set
manually for full scale, then you switch to reflected power to read the SWR.
(I don't have one, so am going from the generic case.)

To do so, you need a continuous output carrier from the rig.  So I'm assuming
that you are keying the rig in FORWARD mode (or whatever it is called), adjusting
the sensitivity control so the meter reads full scale, then switching it to read
SWR.  If the output power changes for any reason you have to repeat this process
to get an SWR reading.  Otherwise, if the sensitivity control isn't set properly for
the output power, the SWR reading will be incorrect.

There are several ways to get the rig to generate a carrier:  I use CW mode
since I have a key connected anyway.  But for those don't, then AM, FM or
RTTY are often used instead.  If you use AM mode then the carrier output
is usually limited to about 20 or 25 watts - is that what you are doing?
Otherwise, the rig should be capable of full output in CW mode.

If you are using SSB, then it is much more difficult to measure the SWR
unless you have a peak reading meter.  That's because there is no output
power until you speak into the mic, and the output power changes with the
voice modulation waveform much faster than the meter can respond.  With
the mic level set properly, you'll probably see around 20 to 30 watts measured
on a non-peak reading meter.  THAT'S NORMAL FOR SSB.  If you crank up the
mic gain to get a higher reading it will distort the signal badly, and you'll splatter
up and down the band.

All of these contribute to uncertainties in both the SWR and output power
measurements - that's why it makes a difference how you are taking them.



Quote

ok now for the very stupid question I don't have the rig hooked to a separate ground as I wasn't sure if it was nessesary as I am running it straight from a 12v Deep Cycle



A separate ground connection shouldn't be needed for proper operation of a
self-contained antenna like a dipole.  I don't bother with them, especially for
portable operation. 

It can change the SWR, however, if you aren't using an effective balun, because
then the outside of the coax and everything attached to it (rig, battery cables,
etc.) become part of the antenna.  In such a case, adding an external ground
connection (or removing one, for that matter) can change the SWR because
you are changing the antenna
.  With an effective balun at the antenna
feedpoint, a ground connection shouldn't have any effect on the SWR.

That's not to say that there aren't cases where you would a ground connection
for some other purpose:  lightning protection is probably the biggest one, if you
are in an area where that is a problem.   But making an adequate ground to
protect your station is an entirely separate topic own its own.
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YONU
Member

Posts: 67




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« Reply #25 on: December 26, 2012, 02:36:32 PM »

well I sent out a message to a couple of Local HAMS to see who is free if nothing else but to send out a couple of test transmissions for me

Thanks Again I will let everyone know how it goes,
Reg
KK4NJC
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YONU
Member

Posts: 67




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« Reply #26 on: December 27, 2012, 05:56:24 PM »

Hey guys I wanted to say thanks I got my antenna working for the most part however I have a question and the local ham I was working with was not sure of the cause so I shot a quick video of the noise to see what you might think it is.

https://www.youtube.com/watch?v=TSkqMuaH5lY&feature=youtube_gdata_player

Thanks,
Reg
kk4njc
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N8CMQ
Member

Posts: 373




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« Reply #27 on: December 27, 2012, 06:45:31 PM »

Your video is set to private and needs a password.
Good to hear you are making progress!
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YONU
Member

Posts: 67




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« Reply #28 on: December 27, 2012, 07:00:34 PM »

ok I changed the video it is now public sorry about that I didn't even realize I had set it to Private
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W5DXP
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Posts: 3613


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« Reply #29 on: December 28, 2012, 08:06:15 AM »

...what you might think it is.

It's one second intervals - like a clock - electric fence timer?
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
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