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Author Topic: kenwood 520  (Read 6181 times)
KC9VZB
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« on: November 29, 2012, 04:44:37 PM »

after cleaning and deox radio works pretty good. waiting for finals parts .issue is there's no meter movement in tune,I don't have a dummy load yet and I'm new at tuning,crippled by dyslexia,going from schematic to radio backwards! I checked resistors on high voltage board finding one that was way off,but still no change after replacing.Don't know if its a big deal,when I can tune into dummy while in transmit. hard on the tubes.I thought I'd get the giant print schematic and go from there,thought I'd stay off the air till I can tune it better. second issue is antennas.ask 5 hams and I get 8 different best for the beginner.What I put up is a dipole,130 feet center fed with coax (the fat stuff)no ballun .I have a fine tuner,and no matter what I do swr is pretty high.logic tells me I need a ballun to get it anywhere near 50 ohms.   
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AC5UP
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« Reply #1 on: November 29, 2012, 07:06:28 PM »

A 130' center fed dipole should resonate somewhere near the bottom of 75 Meters.  And maybe somewhere around 10 Meters.

If you're trying to force it to 40 Meters with a tuner, that is NOT going to work and a Balun will not help you. Remember that a coax-fed dipole is inherently a single band antenna. Coax does not tolerate a bad mismatch or high SWR without going lossy. If you want to try an All-Band Doublet it's the same size but fed with open wire parallel "Ladder Line".

You need to do some reading about antenna theory at two levels... What works, and why it works.
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KC9VZB
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« Reply #2 on: November 29, 2012, 07:30:38 PM »

I was afraid of that,I was on 80 meters when it was best.So I stay on 80 or drop with a ladder line
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W5RKL
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« Reply #3 on: December 12, 2012, 04:46:50 AM »

after cleaning and deox radio works pretty good. waiting for finals parts .issue is there's no meter movement in tune,I don't have a dummy load yet and I'm new at tuning,crippled by dyslexia,going from schematic to radio backwards! I checked resistors on high voltage board finding one that was way off,but still no change after replacing.Don't know if its a big deal,when I can tune into dummy while in transmit. hard on the tubes.I thought I'd get the giant print schematic and go from there,thought I'd stay off the air till I can tune it better. second issue is antennas.ask 5 hams and I get 8 different best for the beginner.What I put up is a dipole,130 feet center fed with coax (the fat stuff)no ballun .I have a fine tuner,and no matter what I do swr is pretty high.logic tells me I need a ballun to get it anywhere near 50 ohms.   

Have you checked the "SG" switch on the 520's rear panel? It must be in the "ON" position.

73s
Mike
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AC2EU
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« Reply #4 on: December 12, 2012, 01:39:07 PM »

I was afraid of that,I was on 80 meters when it was best.So I stay on 80 or drop with a ladder line

A ladder line may help a little, but the harmonic relationship between the 40 and 80M bands is not favorable.
The antenna and the coax are a "system" and always should be calculated as such.
A good investment would be  the ARRL antenna book. Lots of good info on all of this .
 
If you only want a single antenna for several bands an interesting compromise is an OCF dipole.
You can also use a trap type dipole . They fell out of favor due to TVI back in the old days, but probably are more useable with all of the TV changes in the 21st century.
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WN2C
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« Reply #5 on: December 12, 2012, 11:53:56 PM »

135 ft of wire split into 2 equal lengths, fed with 450 ladder line in to a good tuner (even a MFJ 949) with a 4:1 balun will get you on most all bands 80 thru 10.  Fed against ground and you can use it on 160 (albeit won't work well but will work)
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G3RZP
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« Reply #6 on: December 13, 2012, 03:56:18 AM »

Why should a trap dipole give any more TVI than an ordinary dipole?
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AC2EU
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« Reply #7 on: December 13, 2012, 05:47:47 PM »

Why should a trap dipole give any more TVI than an ordinary dipole?

I don't know this from personal experience, but form what I have read. The "decoupled" parts of the dipole could supposedly set up harmonic resonances of their own. Now that the TV bands have moved way north of the Ham bands it's probably a non issue.
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K8AXW
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« Reply #8 on: December 13, 2012, 05:55:02 PM »

Aaahhhhh....'scuse me.... the guy has a problem..... not with an antenna but with his 520!  No meter movement.... remember??  There should be some kind of meter movement even if he didn't have an antenna hanging on the radio.

VZB:  You can tune into a dummy load to your heart's content.  The limiting factor is the heat build up in the dummy load.  However it also needs to be understood that key down time during the tune up should be minimized because this is where it's hard on the tubes.

If you don't have a dummy load, get a piece of coax with a PL-259 on one end, connect it to the 520.  Split out the other end and connect the center conductor to one terminal or wire of a light socket and the shield to the other terminal or wire.  Screw in a 100W light bulb and have at it.

This is what we used before Cantennas were sold.  This isn't a 50ohm load but it works and won't hurt anything.  

If you are able to light up the bulb you can then see the effects of the tuning process by the brilliance of the light bulb and can pretty well conclude you have metering circuit problems.  If it doesn't light you have a problem in the radio besides the meter circuits.

If memory serves me right, the meter also is used to monitor or check your HV.  If you don't have any meter deflection here and you're able to measure HV with a meter inside the radio then you have a metering problem common to all functions of the meter.

After this you can then continue getting 5 answers from 8 guys on this antenna question. This part of your question will surely go on for a few weeks!

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ZL1BBW
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« Reply #9 on: December 13, 2012, 07:00:47 PM »

Dont know about the 520, but make sure that if there is a switch to select what the meter is reading that it is set correctly.

On the 530 it will read ALC IP RF HV.

100% on the light bulb best dummy load ever for 100 watt valve finals you can actually get a feel and see what is happening.


On the antenna front, dump the coax get some ladder line a 4:1 balun just in/outside the shack and off you.
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ex MN Radio Officer, Portishead Radio GKA, BT Radio Amateur Morse Tester.  Licensed as G3YCP ZL1DAB, now taken over my father (sk) call as ZL1BBW.
AC2EU
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« Reply #10 on: December 13, 2012, 08:51:08 PM »

Quote
Aaahhhhh....'scuse me.... the guy has a problem..... not with an antenna but with his 520!  No meter movement.... remember??  There should be some kind of meter movement even if he didn't have an antenna hanging on the radio.

He had no meter movement in "tune" which is low output anyway and if his match is terrible that might be the case.
Tuning these old rigs takes a little practice. At least this one only has drive/plate/load controls, no preselect. Since none of us are there, we can only speculate on a myriad of possibilities...
A bulb would take the antenna out of the equation for sure!

The only way to control the information and feedback, is to try a specific "known good" procedure to set up/tune/test a 520 then see what result is obtained. When all else fails...read the manual!
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KE3WD
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« Reply #11 on: December 14, 2012, 05:34:23 AM »

A '520 can load a bedspring. 
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N4NYY
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« Reply #12 on: December 14, 2012, 04:02:40 PM »

Why should a trap dipole give any more TVI than an ordinary dipole?

That makes no sense. I have a trap dipole and never heard of this. The biggest cause of TVI seem to be antenna (both TV and ham), that were too damn close to each other, as well as excess power in a populated area. I know people that run 100 watts with wires in heavy populated areas, without TVI.

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AC5UP
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« Reply #13 on: December 14, 2012, 06:43:58 PM »

Give it some thought and you realize the traps are essentially low pass filters. The full length of the wire is used on the lowest designed frequency (all traps passing current), then as you go up through the bands each successive pair of traps blocks current to the endmost wires.

So?

In a single band dipole there is no frequency selectivity. The dipole is free to radiate on the first odd multiple of the design frequency as a 3/2 wave wire and every odd multiple above that. In the case of the typical HF trap dipole anything above ~ 22 MHz is limited to the two shortest wire segments. Not the entire antenna. Reason this through and a good argument could be made that an 80 Meter dipole has more TVI potential than a legacy five band trap dipole of the same length...........  ( ? )
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N4NYY
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« Reply #14 on: December 15, 2012, 04:43:17 AM »


Quote
Reason this through and a good argument could be made that an 80 Meter dipole has more TVI potential than a legacy five band trap dipole of the same length...........  ( ? )

He had it the other way though. Regardless, I never knew that. Likely because it did not present itself.


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