| Author |
Message |
    
Bozzman3
| | Posted on Tuesday, March 12, 2002 - 8:59 pm: | 
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Hello! When using a filter, The correct way to measure operating swr would be: radio/amp/meter/filter/antenna?? I know the correct way to read swr when making antenna adjustments it would be: radio/amp/filter/meter/antenna. Is the first example correct?I feel it is so, because this setup allows us to see the effects the filter has on swr. |
Tech181
| | Posted on Tuesday, March 12, 2002 - 11:39 pm: |
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Bozzman3,
The SWR meter is always the last inline. Radio, amp, filter, meter, antenna.
Steve
Tech181
Tech181@copperelectronics.com |
Bozzman3
| | Posted on Wednesday, March 13, 2002 - 7:16 pm: |
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Then how would you know if the low pass filter was stopping unwanted harmonics that the antenna was rejecting ?? |
bruce
| | Posted on Wednesday, March 13, 2002 - 10:24 pm: |
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the only SURE way would be to put a spectrum anlizer in the field of your antenna set the band width wide enougth to see atleast 3 rd harmonic then take readings with and with out the filter now a second method would be a scanner tuned to the frequency you needed to get rid of and take readings and the simplest would be did it fix the problem??? as a rule a good filter will due what it tells you it will do.
bruce |
Bigbob
| | Posted on Wednesday, March 13, 2002 - 10:45 pm: |
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Tech 181;The low-pass is always last to filter harmonics including those made by the rectifying diodes in the swr meter.My mfj filter has .1db loss which changes swr .o6.My meter is between radio and amp so I can monitor any changes in swr in amp itself. |
Tech181
| | Posted on Friday, March 15, 2002 - 9:36 pm: |
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Ahh yes, once again I have made an a** of myself. Yes, the filter becoming part of the feedline and antenna system should be last inline. I just got a chance to read this thread and realized the screwup I hath made.
Steve
Tech181
Tech181@copperelectronics.com |
Bozzman3
| | Posted on Monday, March 18, 2002 - 7:53 pm: |
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4. If the SWR is good until power is applied:
The antenna is not the problem. In this case, it is the amplifier. You have already established that the antenna is properly tuned and in good working order with low SWR, except when power is applied. Assume a ham operator is on 10 meters using a solid state amplifier. With the radio only, the SWR is 1.1:1; when the amplifier is turned on, the SWR jumps to 2.0:1. The amplifier is not only transmitting at 28 MHz, but is also transmitting on a second frequency of 56MHz. This is known as a "second harmonic" (2X the fundamental frequency of 28 MHz, transmitting at 56 MHz). Thus the SWR meter is reading both the reflected signal of the normal frequency and the rejected second harmonic signal. The antenna will not accept energy transmitted at 56 MHz, and returns it all back to the radio, which shows up on the meter as high SWR because the meter can not tell the difference between 28 MHz and 56 MHz. In fact, as much as 30% of the power is at 56 MHz. This is generally due to an amplifier that is not adequately filtered. Adding a Low-pass filter at the amplifier output is the only solution. For best results, connect the low pass filter directly to the amplifier using a barrel connector. This came from wilsons site. When I take a swr reading with the amp on, filter in place and hooked up Radio/amp/meter/filter/antenna --my swr is much lower then without a filter can I measure swr this way? |
bruce
| | Posted on Tuesday, March 19, 2002 - 4:49 am: |
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a sad comment on that amp..... shoot the engineer who designed it |
Jyd
| | Posted on Tuesday, March 19, 2002 - 11:06 am: |
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i went from a palomar 250 with a 2swr to a texas star 350hdv my swr went way down to less than 1.5 |
bruce
| | Posted on Tuesday, March 19, 2002 - 11:58 am: |
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jyd was that amp dirty or just mismatched???? |
Taz
| | Posted on Tuesday, March 19, 2002 - 2:13 pm: |
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THE TEXAS STAR HAVE A BETTER DESIGN! |
409
| | Posted on Thursday, March 21, 2002 - 2:59 pm: |
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Did you look inside the Palomar ?? Some of them have adjustments inside and can be tweaked a little. |
bruce
| | Posted on Thursday, March 21, 2002 - 8:03 pm: |
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maby im getting old but i remember what ALL amps had adjustments
(ant load) (plate tune) (grid tune)
and a few a bias level pot |
Insider
| | Posted on Thursday, March 21, 2002 - 11:59 pm: |
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The issue of harmonics above your fundamental frequency is well addressed and understood by virtually anyone who uses radio gear. But if the transmitter/amp is producing echos above your your operating frequency, is it possible that it's producing echos below your frequency? Sub-harmonics if you will, and if so, then why is that not addressed the way harmonics are? |
409
| | Posted on Friday, March 22, 2002 - 3:59 am: |
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Yea.....me too bruce, those were the good-ol days when you could sit by your rig in the dark and watch those tubes "blue up" when you keyed the mic and modulated the carrier. Brings back memories....... |
bruce
| | Posted on Friday, March 22, 2002 - 7:41 am: |
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Insider the way to supress sub harmarmonics is a band pass filter. My guess they can happen if you mixed a bunch of 2, 3, 4, 5 ect somewhere you get a sub harmonic out of it. Now ive never see that but the mixing of 2 signals produces a add and subtract result.. a lot of numbers .. hummmm anyone ever measured this?? |
Insider
| | Posted on Friday, March 22, 2002 - 4:21 pm: |
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Thanks for your help bruce. |
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