You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
The Feb 2025 Radioddity Giveaway Results are In! Click Here to see who won!

Reply to thread

Message

Unfortunately this only holds true for the output side of LDMOS devices and the only real benefit this offers is the device can hold up to a near infinite VSWR. This is the side of the amplifier that almost all operators get right by providing a decent VSWR from the antenna.

The input gate of a 1500 watt LDMOS is many times more sensitive than the base of an older 100 watt 2SC2879. One watt of extra drive on some LDMOS devices is equivalent to 100% overdrive and virtually guarantees instant failure. Ten watts of extra drive on a 2SC2879 (and we rarely have just one) will push it into saturation but it will almost always survive this if properly cooled.

When you have one large device that has both the dissipation combined with more than enough gain to produce the same power as 10 or more smaller devices, you are playing with fire if you don't have lighting fast protection monitoring the input drive conditions. If that is too much work and you're determined to experiment, buy a 6db attenuator before you wreck the transistor.

Don't rely on your radios carrier or power control to hold it at one watt. They rely on your radios ALC or AMC to hold the output and that reduced level and are often not fast enough to prevent noticeable excursions above that level on sudden audio peaks. You are in a much safer position to let the radio run where it operates reliably and comfortably while attenuating that drive back down to a safe level for the LDMOS device.

<blockquote data-quote="Shockwave" data-source="post: 699721" data-attributes="member: 10882">Unfortunately this only holds true for the output side of LDMOS devices and the only real benefit this offers is the device can hold up to a near infinite VSWR. This is the side of the amplifier that almost all operators get right by providing a decent VSWR from the antenna.The input gate of a 1500 watt LDMOS is many times more sensitive than the base of an older 100 watt 2SC2879. One watt of extra drive on some LDMOS devices is equivalent to 100% overdrive and virtually guarantees instant failure. Ten watts of extra drive on a 2SC2879 (and we rarely have just one) will push it into saturation but it will almost always survive this if properly cooled.When you have one large device that has both the dissipation combined with more than enough gain to produce the same power as 10 or more smaller devices, you are playing with fire if you don&#039;t have lighting fast protection monitoring the input drive conditions. If that is too much work and you&#039;re determined to experiment, buy a 6db attenuator before you wreck the transistor.Don&#039;t rely on your radios carrier or power control to hold it at one watt. They rely on your radios ALC or AMC to hold the output and that reduced level and are often not fast enough to prevent noticeable excursions above that level on sudden audio peaks. You are in a much safer position to let the radio run where it operates reliably and comfortably while attenuating that drive back down to a safe level for the LDMOS device.</blockquote>

[QUOTE="Shockwave, post: 699721, member: 10882"] Unfortunately this only holds true for the output side of LDMOS devices and the only real benefit this offers is the device can hold up to a near infinite VSWR. This is the side of the amplifier that almost all operators get right by providing a decent VSWR from the antenna. The input gate of a 1500 watt LDMOS is many times more sensitive than the base of an older 100 watt 2SC2879. One watt of extra drive on some LDMOS devices is equivalent to 100% overdrive and virtually guarantees instant failure. Ten watts of extra drive on a 2SC2879 (and we rarely have just one) will push it into saturation but it will almost always survive this if properly cooled. When you have one large device that has both the dissipation combined with more than enough gain to produce the same power as 10 or more smaller devices, you are playing with fire if you don't have lighting fast protection monitoring the input drive conditions. If that is too much work and you're determined to experiment, buy a 6db attenuator before you wreck the transistor. Don't rely on your radios carrier or power control to hold it at one watt. They rely on your radios ALC or AMC to hold the output and that reduced level and are often not fast enough to prevent noticeable excursions above that level on sudden audio peaks. You are in a much safer position to let the radio run where it operates reliably and comfortably while attenuating that drive back down to a safe level for the LDMOS device. [/QUOTE]

Top Bottom