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Amp That Does NOT Make SWR Rise

U

unit511

Member
Jan 21, 2012
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Want a amp that does not make swr change much when engaged. I am sure you guys would know. Don't want mega watts just alittle something for dx'ing. Also I would like to be able to adjust output so I don't bother my neighbors. Max. maybe 300 watts on ssb? No tubes and must be either mobile 13.8vdc or a base 120vac.Thanks .....
 

i dx alot on 10 and 11 meters with out an amp. mother nature is wonderful sometimes.

but when i feel i need a little power to make or keep a contact a little longer i have a tnt350hd, it is a two pill, and it is all I really need. I purchased from xforce amps. Google for their website.
 
An amplifier does not change SWR, unless you get to power levels that the antenna or transmission line starts arcing internally.
SWR is essentially a ratio of forward to reflected power. As your forward power increases, the reflected power will also increase. The ratios should remain constant.
Perhaps what you are experiencing is an increase of harmonics or other spurious outputs. These will often be reflected by a tuned antenna and appear to cause the SWR to increase. What you should be looking for is an amplifier that is linear and does not create spurious output. This can also happen if you over drive an amplifier. Back off your power a little and the results may be promising.

To better explain, at work I check antenna frequency response with signal level of about 0.1 watt. The transmission line can be several hundred feet long. There are multiple transmitters combined to the antenna. Transmitter power ranges up to about 20kW with power to the antenna up to about 70kW. The expected SWR is better than 1.1:1 and it remains the same at full power. We have experienced major failures in which transmission lines have melted and square steel tubes have had large holes burned in them. Once that starts all bets are off, but quite often the SWR remains reasonable until the antenna has been severely damaged. At a few hundred watts there is no chance of this happening. :)
 
So when I check my swr with the amp on and I see the swr is no longer 1.1:1, I will not harm my finals? Yet on am my swr warning light flickers abit.
 
There is nothing you really can do but add a longer jumper. Some cheap amps are not quite at 50 ohms and then you see this happen. Just make sure your antenna is set right barefoot, the amp is grounded good, and you have a 6 or 9 foot jumper and roll with it. I have found that most Palomars have some issues on Hi power so run lo or med. Texas Star is alittle better but still mass produced. Something like the TnT from X-Force should be right on the money.
 
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Woooo! It's been a while.
I'm having an SWR problem as well when a Carl Built HD400 is keyed up. SWR is normally 1.2 on ch 1 & ch 40. When keyed, the SWRs on ch1 fluctuate 1.7-2.5 (LP-100a meter), but on ch 40, they are rock solid steady at 1.2. Weird.
Using rg400 coax 3ft jumper from radio to amp, 6 ft from amp to meter, then Sirio 827 antenna.
Carl said to do what 9C1Driver mentioned...use a longer jumper. I went from 3 ft to 6t. Not much changed.
Weird that the FatBoy 4pill doesn't affect the SWRs at all, but this Carl Built one sure does.
 
What kind of SWR meter are you using? If it's the kind that you have to switch to adjust it to full scale (sometimes with a switch marked "CAL" or "FULL SCALE") and then switch it to "SWR", then the meter is likely the problem. It's responding to the change in forward power with a change in reflected power. If you set it for a full scale reading of ten watts forward power and it measures, say, two watts of reflected power, that two watts won't, or shouldn't, change as long as the ten watts output remains constant. But if you increase the output power to 100 watts, the reflected power should increase to somewhere around 20 watts.

This type of meter HAS to be re"calibrated" every time you change power level or frequency/channel.
 
If your vswr rises with increased power, there is an issue somewhere with the transmission line and/or antenna.
 
Beetle said:
What kind of SWR meter are you using? If it's the kind that you have to switch to adjust it to full scale (sometimes with a switch marked "CAL" or "FULL SCALE") and then switch it to "SWR", then the meter is likely the problem. It's responding to the change in forward power with a change in reflected power. If you set it for a full scale reading of ten watts forward power and it measures, say, two watts of reflected power, that two watts won't, or shouldn't, change as long as the ten watts output remains constant. But if you increase the output power to 100 watts, the reflected power should increase to somewhere around 20 watts.

This type of meter HAS to be re"calibrated" every time you change power level or frequency/channel.
Click to expand...

I agree. I have a WM-1, and it shows higher than normal SWR for some reason. I have heard they sometimes have RF bleed issues.
 

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