>Rich,
>
>I am rapidly getting the feeling that I totally misunderstood what everybody
>meant by "hot switching". I thought it meant that the transceiver was seeing
>undesirable transients because it changed modes - ie receive to transmit -
>before the amp could switch and present the proper load on the transceiver.
>Now I'm getting the feeling that you are referring to opening and closing
>SB220 relay contacts while they are carrying current.
>
>Could you help clear up what you mean by hot switching?
>
Hotswitching usually means that the transceiver begins delivering RF
before the amplifier relay contacts have closed and stopped bouncing.
The way to tell if this is the case is to watch the SWR indicator in the
transceiver. If the SWR indication briefly spikes upward when the VOX
trips, or the PTT button is pressed, hotswitching is indicated.
A better test is to send CW dashes, watch the SWR indicator on the
transceiver, and vary the speed.
If RF is on the amplifier relay's contacts during contact-bouncing, rapid
contact errosion takes place.
Some modern radios begin producing RF in 5mS. If the amplifier relay can
not beat 5mS, it will get beat up. The circuit shown in Figure 7B on my
Web site will switch in 2mS or less. [circuit also in "The Nearly
Perfect Amplifier", 1-94 *QST*]
- - (note: a Jennings RJ-1A vacuum relay will not switch fast enough to
beat modern radios unless it is driven with a v-limited {100v - 160v}
current source instead of a fixed voltage {usu. 26v} source.)
Rich...
R. L. Measures, 805-386-3734, AG6K
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