| Author |
Message |
    
dcobb
| | Posted on Saturday, June 15, 2002 - 8:55 pm: | 
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I have an 'older' Midland 77-101B radio and want to run it into a KL-40 amp. I've checked the radio with a meter and it's putting out 3W. I've seen several posts that suggest limiting the KL-40 input to around 1W, but the KL-40 specs list an input range of 1-5W for AM operation.
I'm looking for opinions here - am I safe enough running 3W into the KL-40 or do I really need to lower the radio power some?
I don't know how to reduce the TX power myself. I've seen some online references to adjusting AM power on this radio by adjusting "L304, L305, and L306", but I don't exactly know how to do this. Are these pots to adjust? I'd just as soon not do anything dumb here, but I have a Master's Degree in EE, so I'm not totally out of my comfort zone.
Thanks in advance for the help!
DC |
Tech181
| | Posted on Sunday, June 16, 2002 - 12:16 am: |
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dcobb,
No more than a watt. Even a 1/2 watt drive is more than sufficient. You can get away with up to 1 1/2 watts if you are not long winded. That is the absolute limit.
Adjust L304, 305, and 306 in order for the desired carrier level in AM mode, no modulation.
Steve
Tech181
Tech181@copperelectronics.com |
Tech671
| | Posted on Sunday, June 16, 2002 - 7:20 am: |
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The objective is to get whatever amp you use to have a carrier-to-peak ratio of 1:4. So if you have an amp capable of 40w you would want a 10w carrier coming out of the amp, setting the radio accordingly to achieve this. The way your radio is set it's likely to have a 25-35w carrier with little forward power when you talk....resulting in a distorted or muffled audio and driving the (blank) out of the little amp.
With your radio you could adjust the tuners you mentioned to bring the carrier power down achieving the proper ratio, but it may take a little back and forth to get it to sound right/ work right. |
dcobb
| | Posted on Sunday, June 16, 2002 - 10:39 am: |
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The bummer part of adjusting the power downward is that I can't really use the radio by itself anymore without the amp.
DC |
Biged
| | Posted on Sunday, June 16, 2002 - 5:43 pm: |
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dcobb,
You will be suprised how far you could talk on 1 watt. ANTENNA ANTENNA ANTENNA !!! |
Taz
| | Posted on Sunday, June 16, 2002 - 8:30 pm: |
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hehe, i talked skip with 1 watt on 26.105 a few months back, of course i was swinging about 300.
hehe |
Tech671
| | Posted on Monday, June 17, 2002 - 5:28 am: |
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There's another method DC, but I'd have to have the radio to do it. |
dcobb
| | Posted on Monday, June 17, 2002 - 10:47 am: |
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Here are two follow-up questions:
1. I've seen where some radios have High/Medium/Low power settings on the front panel. If I were to get one of these radios and set it for Low power, would that probably be sufficent?
2. I have two coaxial power attenuators that can handle at least 5W. If I put one of these inline with my current radio, would that be okay? (The range of power coming out of the attenuator would be either 0.5 or 1.5W, depending on which I used). Would this adversely affect my SWR?
Thanks...
DC |
dcobb
| | Posted on Monday, June 17, 2002 - 9:39 pm: |
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Think I may be on to something. I've seen some positive posts regarding the Cobra 45WX handheld. There's a 5-minute mod to add extra channels and it also has a low power (1W) setting. Feedback I've seen on Copper's forums indicate it sounds good, plus it has weather channels, external antenna/microphone hookups, etc.
This sounds like a good solution to my problem. |
ChillyDog
| | Posted on Tuesday, June 18, 2002 - 10:10 am: |
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dcobb,
Putting attenuators in line with your radio's output will reduce to drive to your amp, but will also reduce your receive sensitivity.
Best Regards,
Bob |
dcobb
| | Posted on Tuesday, June 18, 2002 - 11:52 am: |
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Good point on the receive sensitivity. I'm attenuating in both directions.
I think the handheld is the way I'm leaning. The 1W level should be fine for the amp and it's got some unique features.
DC |
Dcobb
| | Posted on Wednesday, June 19, 2002 - 6:15 pm: |
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My KL-40 arrived and I tried it out. Here's some data from my test. Does this seem about what I should expect? It was a little lower than I expected.
The gain I measured is about 6 dB. With 1W in, I measured 4.5W out. With 2W in, I measured 8W out. At full power in (4.4W), I measured 17.5W out. I'm using a good multi-range cross-needle SWR/power meter, so I believe the readings.
My radio has never been peaked, modified, or adjusted in any way. I'm using a new Wilson 500 antenna. The manufacturer spec lists the input range as 1-5W and the output at 25-35W. I'm not getting that amount of power out of the unit. The readings were made with the input voltage at 13.6V.
Any thoughts? |
Taz
| | Posted on Wednesday, June 19, 2002 - 10:21 pm: |
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Is that deadkey ratings?
when testing for max swing dont whistle say auuuuudiiiooooooo |
Tech671
| | Posted on Wednesday, June 19, 2002 - 11:28 pm: |
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The KL40 is not rated at 25-35w for AM carrier. This is the maximum output peak or PEP. When you put a 1w carrier in you should get around 8-10w carrier out at 14v with a 1.5 or less swr. When you modulate the carrier (speak) your transmitter should do around 10-12w, and the KL around 25-35w. |
Dcobb
| | Posted on Thursday, June 20, 2002 - 6:52 am: |
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Those are basically deadkey ratings, but I can't see any significant changes in the meter when I modulate. The meter has settings for average and peak power, but they both give me the same readings. Maybe this is partially a meter issue?
So, would you agree that the amp is performing as I should expect? |
Dcobb
| | Posted on Thursday, June 20, 2002 - 9:04 am: |
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One more note, since you mentioned it: my swr varies across the band, but is less than 1.4 at all times. |
Taz
| | Posted on Thursday, June 20, 2002 - 9:07 pm: |
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whats your radios output power?
what does it swing? |
Tech671
| | Posted on Thursday, June 20, 2002 - 9:45 pm: |
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If you are using a radio shack meter, it has poor design for reading forward modulated power (peak). Basically it doesn't do it at all. Just remember the magic rule 1:4. 1 part carrier to 4 parts peak in the final out transmitter. Meaning If your KL40 is rated at 40w ssb, then your AM carrier out should not exceed 10w. Adjust your radio accordingly. |
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