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Author Topic: Dipole Tuning for Newbie  (Read 641 times)

Posts: 2

« on: November 25, 2003, 05:02:53 PM »

Hi All,

I just received two large boxes of radio equipment from a relative who has fallen out of 'tune' (pun intended) with the hobby in recent years.  The main parts are: an Argosy 525D, 40-meter dipole, and a MFJ Deluxe Versa Tuner II.

I just got around to stringing up the dipole today, and about 10 feet of one side slope down at about 45 degrees.

I came in, got the radio and tuner hooked up, and figured 40 meter CW (in the novice area) would be the best place to start.  The tuning directions i have say to tune the antenna without transmitting until you hear the loudest noise in the receiver, then do a little touch-up while transmitting.  I did that, and have the antenna matched at very close to 1:1.  However, the S-meter on the argosy reads S7 (S5.5  on 20m when I tried), which seems very high.

So the gist of everything i've said so far is:  Is it correct/acceptable to see a noise floor so high, or is something wrong on my end?

Thanks and 73,

Posts: 1484

« Reply #1 on: November 25, 2003, 05:10:36 PM »

If you've got close to 1-to-1 with a little transmitting power out, that S7 is just noise.  I've noticed a lot of QRN lately--though not usually S7!  If you're feeding that dipole with ladder line, try it on other bands above 40 meters and see if the noise goes away there, or try tuning up and down the band and see if it changes--my computer monitor throws about an S5 at certain frequencies but the noise spikes are only 20khz wide so I can tune around them.  (And if I want to operate where there is a spike, I just change the refresh rate on the monitor, which throws the spikes to a different area.)  If you can hear anybody through the noise, you might try working them and see if they're hearing the noise, too.  By the way, if you're using coaxial cable to feed that dipole, you might consider trying ladderline instead--with the tuner, you can use that antenna on all bands above 40 meters as well.  Let us know how this goes!  73--Ken AC4RD

Posts: 2

« Reply #2 on: November 25, 2003, 05:20:53 PM »

Yes, the antenna is fed with ladderline with about 6 feet of coax to make the hookup to the tuner.

After trying it on all bands, 15 and 20 meters show S5 noise, 40 meters has S7, and 80 (which still tuned to a little over 1:1) was around S6.  Can anyone by a rig confirm something in this range?

Just found out my keyer won't power on, so I'm off to rip that apart and see what's biting it's tongue.  (that or SSB).


Posts: 17483

« Reply #3 on: November 25, 2003, 06:44:39 PM »

I have the original Argosy 525, and  I don't think the
noise level usually runs that high.  But many noise
sources are localized - noisy powerlines, motors,
vacuum cleaner, aquarium heater, furnace blower, etc.
It is also possible that the S-meter gain is set too

A good first step is to disconnect the antenna (maybe
by switching the tuner to an unused position, or a
dummy load.)  If you still have a high S-meter reading
it must be in the radio, otherwise it is coming down
the coax from the antenna.  If the noise drops, then
you have enough receiver sensitivity.

Even though my Argosy is over 20 years old, it still
digs out weak signals better than my newer rig.

Posts: 310

« Reply #4 on: November 25, 2003, 09:42:39 PM »

How high up is the dipole? I had to raise mine higher to get rid of the noise generated in my house. One of my TVs has a switching power supply that is about s5-7 and my AC/Heater fan is about s-7 on almost on all bands. You could start unpluging appliances and turning circuits off to try and find if the noise is in your house.

Posts: 1484

« Reply #5 on: November 26, 2003, 09:30:33 AM »

I agree with the others; that sounds like a LOT more noise than usual and you've probably got some local source that is causing it.  I turned on the rig this morning getting ready for work and 40 meters (down around 7005) was very quiet--except for the /KH9 station and everybody working him!  ;-)  One step that might help you a lot in finding the source of the noise is to look for a local ham club or hams living nearby--they may be hearing it also, or may know what's up.  What sort of noise is it?  Harsh buzzing is often caused by an electrical appliance or device, I think--but I don't know much more than that.  Oh--and I think the ARRL has information on its website about this--worth taking a look there also!  Good luck and please update us with how you're doing in tracking it down!  73!  --Ken AC4RD
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