| Author |
Message |
    
Lazylizard
| | Posted on Tuesday, February 03, 2004 - 10:39 pm: | 
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This situation is hypothetical of course....but what if you had a Uniden PC76XL radio with a DK of 3 watts and a swing of 22-25 watts or so.....hooked to a Palomar Lizard 250 HD (Green Face with two 2290 pills).....feeding a Wilson 1000 mag mount on the roof of a 3/4 ton Chevy Pickmeup truck.
And this happened:
On HIGH power setting.....everything is happy. SWR is 1.1 to 1.2 to 1. Signal gets out strong with good radio checks. Cheapo Ratshack (not accurate I know but it gives a reference) meter shows 50 watt DK, 200 watt swing. All is cool.
On MEDIUM power setting.....everything is so-so. SWR is 1.4 to 1.5 to 1. Signal gets out strong with good radio checks. Cheapo Ratshack (not accurate I know but it gives a reference) meter shows 40 watt DK, 185 watt swing. All is so so.
On LOW power setting.....everything goes south. SWR is off the chart and red antenna warning LED lights up on radio. Signal gets out muddy on radio checks. Cheapo Ratshack (not acurate I know but it gives a reference) meter shows 30 watt DK, 150 watt swing. All is sad.
What could this be? A local radio guy said it could be a harmonic distortion in the low setting that could possibly be cleared up with a low pass filter....or something could be wrong with the switch...and to just go ahead and run on high or medium. What do you think?? I believe the low and medium modes on the power switch add resistance to the power circut.
Why would there be a huge amount harmonic distortion in low, a small amount in medium, and none in high? |
Bigbob
| | Posted on Tuesday, February 03, 2004 - 11:41 pm: |
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If all was well,without expensive test equipment no-one can tell the difference between 150 and 200,so why bother with 150,leave it on high and run it,it'll be cool and you'll be cool,I mean that's the point of an amp.For people to really notice a diff. in your audio you will have to get a 1-pill or a 4-pill amp,1/2 or twice the power,that switch is just something for you to play with,I got a palomar 250 with 2 1446 pills in it and it does the same as yours,but I got it for the 250 not the lower settings,the same for my boomer 400,I know this isn't the answer you were looking for,but in practice it is the most practical one. |
Lazylizard
| | Posted on Wednesday, February 04, 2004 - 12:53 am: |
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Bob....so yours does the exact same thing.....on high it is! Thanks |
sparkomatic
| | Posted on Wednesday, February 04, 2004 - 7:17 am: |
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My first amp was a gray 150 and it behaved the same way.......very high SWR on low and med stages but excellent swr on high and max stages.
Every stock amp I ever had did this but my comp amps don't do this.
I bet if you checked the swrs on low with modulation they would drop to normal.....why I don't know. |
Lazylizard
| | Posted on Wednesday, February 04, 2004 - 6:00 pm: |
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I opened up this amp....the amp has large resistors in line on the input signal from the radio when on either low or medium.
A friend of mine suggests that I am getting a signal feedback reflected back to the radio because my dead key is set to low to overcome the resistance of these resistors. Of course the high setting has no resistance in line and works fine.
My dead key is set at 3 watts. My friend also suggested a higher dead key of 7 - 8 watts would make it work fine on low and medium. He said since it is a HD amp (high drive) it needs an increased deadkey over a normal amp to work properly on low and medium settings.
What do you think of this idea? |
Bigbob
| | Posted on Wednesday, February 04, 2004 - 11:06 pm: |
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Try it,all these amps from palomar,boomer,shooting star are cheaply made,those are swamping resistors,supposedly matched to the input impedance to absorb some rf energy,but an L-pad one resistor in series and one to ground for both settings works better,but this should be done by a tech with experience in this,L-pads add cost so a swamping resistor is a compromise,I doubt that increasing the input will change anything positively,you see your radios output should be 50 ohms impedance,now look at the resistors,if they have a number with an inverted horseshoe at the end thats the ohmic value,if it's larger than 50 divide it by 50 that's your swr,if smaller than 50,divide 50 by the smaller that's your swr for that one,this is an over simplification but should be close,if the resistors have color bands instead,then I don't have time or space to give you the various designations,maybe someone who can type faster than I can give it to you.You say the amp is hi-drive,the 2290s show 8 watts drive per pair,not to high,my sd1446s show 10 watts per pair,and my palomar 250 is considered a low drve amp and I'm putting 5 watts through them dead key and I still have the same problem you have on the lower settings.One thing though I don't use any of my amps on AM just SSB my neighbors don't complain and the amp finals love me for it,that dead key really heats things up,both literally and figuratively.Bigbob |
Kiwikid
| | Posted on Thursday, February 05, 2004 - 1:07 pm: |
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Hi Team,Lazylizard where are you placing the meter?
Have you set your station up like this
Radio > meter > amplifier > antenna.
If so your amp input load resistors may be dud.Refer to BIGBOBs ideas or see a tech.
Have you set your station up like this
Radio > ampifier > meter > antenna.
You may have unusal radio frequency harmonics generated by the amplifier and or bad filtering or the design of the amplifier.See a tech. re-design or replace the amplifier with a better quality model.
73
CEF 195
Kiwi Kid |
ryan
| | Posted on Thursday, February 05, 2004 - 8:14 pm: |
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a bad antenna can also make a clean transmitter filthy on the radio dial |
Johnhenre
| | Posted on Friday, February 06, 2004 - 8:35 am: |
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JUST A TOUGHT SOLDER A 1000MFD MICA DIPED CAP. ACROSS THE OUTPUT TRANSFORMER ALONG WITH THE ORTHERS,AND SEE WHAT HAPPEN'S TO YOUR SWR AND TAKE NOTE OF YOUR OUTPUT WATTS? LET ME KNOW WHAT YOU SEE? |
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