OK, here's my situation. Shockwave antenna with 50ft of lmr-400 into an MFJ meter with a 6ft lmr-400 jumper into the radio, and I know the radio swr may not be perfect but at the radio it is showing a 1.0 swr. I also tested the swr without the radio plugged in with a Nano VNA and swr is around 1.06swr. I can deal with that. that's fine. Now, when I add my amp inline, it is setup as from antenna into mfj meter then 6ft of lmr-400 into amp then 6ft lmr-400 into radio. Now after the amp is added, the swr on the radio shows as 1.9 swr. The amp is a brand new Davemade. So shouldn't be anything wrong with the amp. What do I need to do to get the swr lower between radio and amp?
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radio and amp matching....
- Thread starter CorruptHawkeyez
- Start date
This is a common issue with almost any custom amp. In most setups operators don’t see the input swr to the amp so they never know if it’s high/low. The issue is the input impedance on the Davemade amplifier. This can be rectified by adding an adjustable cap(464 or 468 mica adjustable) and or coil to the input inside the amp. Sometimes increasing the negative feedback on an amp will also rectify this issue. In my mind 1.9 is acceptable. I never trust the swr meter on the radio so using a more accurate meter between radio and amp would be advantageous. You can’t see the input swr into the amp unless it’s keyed.
Additional information would help such as what radio and how much power are you driving the amp with? Is the amp a straight 4 pill…6 pill…8 pill 2 x 4???
Brad
Several of us have had that issue with xforce, Fatboy, Carlbuilt and Texas Star.
See this thread by ShadeTreeMechanic: https://www.worldwidedx.com/threads/x-force-600hd-smoked.249976/page-12
Additional information would help such as what radio and how much power are you driving the amp with? Is the amp a straight 4 pill…6 pill…8 pill 2 x 4???
Brad
Several of us have had that issue with xforce, Fatboy, Carlbuilt and Texas Star.
See this thread by ShadeTreeMechanic: https://www.worldwidedx.com/threads/x-force-600hd-smoked.249976/page-12
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It is a straight 4 pill. I am using an Anytone 6666 to drive it. I was told the maximum deadkey after the amp that I should see with the amp on would be around 100w. I've already had to send the amp back due to popping a transistor and now I'm scared to put the amp back inline with the 1.9swr between radio and amp. Radio max output is around 70-80w.
Also, I don't know if it had anything to do with popping the transistor but I did xmit on FM for about 5-10 secs of talk time each transmission to a dx contact. Afterwards I switched back to lsb and within about 5 minutes lost full output power. Could transmitting on FM have heated the transistor too much?
Also, I don't know if it had anything to do with popping the transistor but I did xmit on FM for about 5-10 secs of talk time each transmission to a dx contact. Afterwards I switched back to lsb and within about 5 minutes lost full output power. Could transmitting on FM have heated the transistor too much?
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The higher swr between radio and amp will not adversely affect the amplifier only the radio. The Anytone has swr protection built in so should shut down the radio if it exceeds you set limits.
What was the cause of popping a transistor?
What was the cause of popping a transistor?
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As long as the dead key out of the amp was at the same 100 watt level as AM, FM will not harm the Amp.
It is when operators see 400 watts swing on AM and then try to run 400 watt dead keys on FM that you have a problem.
The 100 watt limit the builder recommended is for AM or FM.
Is this amp class c ?
Variable ?
Pictures of the board would help.
If it is a " newer" Dave made coming out of the camp they have been building them with negative feedback....well at least some of them.
It does sound like a input tune issue.
73
Jeff
It is when operators see 400 watts swing on AM and then try to run 400 watt dead keys on FM that you have a problem.
The 100 watt limit the builder recommended is for AM or FM.
Is this amp class c ?
Variable ?
Pictures of the board would help.
If it is a " newer" Dave made coming out of the camp they have been building them with negative feedback....well at least some of them.
It does sound like a input tune issue.
73
Jeff
I believe the amp to be AB biased. I have ran it on SSB with crystal clear audio reports. I am getting around 700w on SSB just using the Anytone to drive it and my MFJ 891 meter reading the output. The day I used FM, I seen around the same amount of wattage on FM as I was seeing on SSB PEP. So may have had too high of a carrier from the radio into the amp on FM?
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If it is dead keying 700 watts, that's too high, way to high.
With the Amp inline and keyed up its not the antenna your radio sees , it is the input of the amp.
The thread linked above shows a way to approach this problem.
73
Jeff
With the Amp inline and keyed up its not the antenna your radio sees , it is the input of the amp.
The thread linked above shows a way to approach this problem.
73
Jeff
If the ops is using 6ft of lmr 400, it sounds like he was trying to use a 1/4 wave length. 6ft is for 213, itsvel factor is .66 I think. I think lmr is much faster And therefore a 1/4 wave is a different length. Try using a 1/4 wave length coax, see if it makes a difference. Unless a load is Purely resistive it can make a difference.
I suppose it is possible but I really doubt your amp is AB. Davemade is known for their class C amplifiers. On their web site it shows a 40 dollar option to add a SSB delay on your amp. Unless you had a very specific conversation with them on building you a biased amp for SSB use you will have a class C amp.
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I would not worry about it but if it bugs you a simple fix would be try a 3 foot, 6 foot, or 9 foot jumper and see which one your radio likes to see. The issue is with your amp and is very common with cb amplifiers. So if you don't want to have to open up your amp and try to have it tuned to 50 ohm's the jumper swap is an easy way to fool the meter in your radio.
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