hello all i have a buddy that is having a pronlem. is running an antron 99 for an antenna and used to run a t.s.350hdv. when amp was on or off he ran around a 1.3 swr. he recently picked up a palomar 300a base amp and whenever he turns the amp on his swr's skyrocket to 4 plus. now at 4 plus the amp is doin the power it is supposed to, he recalibrated his meter for the power jump, checked all connections and everything seemed to be right. but for some reason he cannot get the swr to drop down, could anyone help me out?
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palomar high swr
- Thread starter 123michigan
- Start date
If you look at the plate-cap connections on the four final-stage tubes, you'll probably find ONLY a skinny bare wire joining each of the four cap clips to the ceramic pillar (plate choke) at the center of them.
When it was built, each of those bare wires had a ferrite "bead" slid over it. These served as parasitic-suppressor chokes. Trouble is, they would get hot, split apart and the broken pieces disappear out the holes in the lower cover.
Most of the time, you'll still see these tiny, black "beads" on the plate-cap wires of the two driver tubes. OR, you'll find a conventional-looking resistor with four turns of wire coiled around it on each of the two driver tubes' plate-cap clips.
Adding a conventional "parasitic choke" with four turns of wire around a 47 ohm 2-Watt resistor to each final-tube plate-cap clip (in place of the bare wire) will usually fix or at least improve this problem.
Without those chokes (or the ferrite beads) the amplifier pumps out additional frequencies besides the channel your radio is feeding into the amplifier. Those 'extra' frequencies will cause the SWR meter to read high, even though the antenna checks okay with the barefoot radio.
Not sure where I have a pic of this 'fix', but I'll look around.
Oh, and about that "recalibrated his meter for the power jump", was playing pin-the-tail-on-the-donkey. His meter is not calibrated any more. No big deal, but the power readings won't be trustworthy, anymore. The extra frequencies will tend to 'fool' a wattmeter, along with the SWR scales.
The meter is only calibrated if he used a 50-ohm dummy load with little or no SWR. No big deal, but the numbers he reads from that meter now are just that, "numbers", not a measurement. In the same way that moving the red line up on your tach doesn't keep the valves from floating at high RPMs.
73
When it was built, each of those bare wires had a ferrite "bead" slid over it. These served as parasitic-suppressor chokes. Trouble is, they would get hot, split apart and the broken pieces disappear out the holes in the lower cover.
Most of the time, you'll still see these tiny, black "beads" on the plate-cap wires of the two driver tubes. OR, you'll find a conventional-looking resistor with four turns of wire coiled around it on each of the two driver tubes' plate-cap clips.
Adding a conventional "parasitic choke" with four turns of wire around a 47 ohm 2-Watt resistor to each final-tube plate-cap clip (in place of the bare wire) will usually fix or at least improve this problem.
Without those chokes (or the ferrite beads) the amplifier pumps out additional frequencies besides the channel your radio is feeding into the amplifier. Those 'extra' frequencies will cause the SWR meter to read high, even though the antenna checks okay with the barefoot radio.
Not sure where I have a pic of this 'fix', but I'll look around.
Oh, and about that "recalibrated his meter for the power jump", was playing pin-the-tail-on-the-donkey. His meter is not calibrated any more. No big deal, but the power readings won't be trustworthy, anymore. The extra frequencies will tend to 'fool' a wattmeter, along with the SWR scales.
The meter is only calibrated if he used a 50-ohm dummy load with little or no SWR. No big deal, but the numbers he reads from that meter now are just that, "numbers", not a measurement. In the same way that moving the red line up on your tach doesn't keep the valves from floating at high RPMs.
73
I see those beads on my 300A....not very promising and none on the finals.
123michigan I know this is hella old thread but I think there are 2 caps for swr, 1 for the low side thats under the drivers and 1 for the high side behind the high/low switch.
123michigan I know this is hella old thread but I think there are 2 caps for swr, 1 for the low side thats under the drivers and 1 for the high side behind the high/low switch.
These are input-matching adjustments.
You set them with a SWR meter IN BETWEEN the radio and the amplifier.
The one on the back of the High/Low switch is for low side only. Tune the final for best modulated swing, and then set the trimmer behind the High/Low switch for lowest SWR on the meter between the radio and amplifier.
For High side, you'll need to make sure the driver tune on the rear is peaked, then you'll find that the Load and Tune for the final will peak at a slightly-different position than they did for Low side. Now set the trimmer under the driver tubes for lowest input-side SWR.
This does nothing for the SWR on the output side. These are input-side adjustments only.
73
You set them with a SWR meter IN BETWEEN the radio and the amplifier.
The one on the back of the High/Low switch is for low side only. Tune the final for best modulated swing, and then set the trimmer behind the High/Low switch for lowest SWR on the meter between the radio and amplifier.
For High side, you'll need to make sure the driver tune on the rear is peaked, then you'll find that the Load and Tune for the final will peak at a slightly-different position than they did for Low side. Now set the trimmer under the driver tubes for lowest input-side SWR.
This does nothing for the SWR on the output side. These are input-side adjustments only.
73
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