Power Amplifier trigger signal

[Patrick Anglum]

I bought this https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.ebay.com%2Fitm%2F314893484937%3Fmkevt%3D1%26mkpid%3D0%26emsid%3De11051.m43.l1123%26mkcid%3D7%26ch%3Dosgood%26euid%3D908e0031b7484b4ea6076acad9123e84%26bu%3D43154424851%26osub%3D-1~1%26crd%3D20231120185100%26segname%3D11051&data=05%7C01%7C%7C49672edcc28741b64d7b08dbea345082%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638361282641753531%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=WH65dd9vaHlxVDmMoNSfbbqQQTrDhm%2FrSBflfdWjNqk%3D&reserved=0

power amplifier.  But I'm not sure how to tell it to go into transmit mode.

I know the Hermes supplies a ground via Q5, but I'm not sure what the PA wants.

For some reason that I can no longer remember I thought the PA wanted +5vdc to go into transmit mode.  I emailed the seller asking this question and this is what I got back:

"PTT trigger level: +VCC-2V (low trigger), GND+5V (high trigger)"

The power for the PA is 12-16VDC.

Does anyone have experience with this PA?

Thanks,

Pat N6XTM

[Pierre Martel]

High Pat,

From what I could find on the web, this is the schematic of the amplifier
https://neatcircuits.com/pix/pa70-sch3.jpg

You can see that the ptt in is feed by a pair of 10 k resistor in serie that drive the base of a PNP transistor, and that transistor drive back the relay and the 7805 regulator that set the PA bias voltage. 

The PTT pin should be more than 5 volt to go in to TX and lower than 2 volt to go into RX. 

The best way to do this would be the put the pin that have the voltage on the ptt connector of the amp to the ext ptt line RCA jack center pin of the Hermes lite 2 and connect the gnd of the amp connector to the RCA jack ring of the hermes lite. 

THis should provide the ptt line with the right signal as when the EXTPTT center pin get sent to ground on PTT ( Usually by default) this should put the transistor in conduction and feed the bias and the relay to put the amp in TX mode. 

Hope this helps

Pierre

VE2PF

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[Evan Hand]

Pierre,

The PTT transistor is a PNP, not an NPN.  The PTT signal will turn on Q* when connected to ground via a relay contact or open collector type of PTT.  I recommend a relay for the Hermes Light 2.

73

Evan

AC9TU

[Patrick Anglum]

Just be sure we are all on the same page, the Hermes will put a ground signal out EXTTR (via Q5) when the Hermes is transmitting.  I have tested this and found it was correct as I described.

The question is what do I need to do with this ground signal to activate the PA switchover on the amp.

If the schematic that Pierre found is accurate it looks to me like putting a short across pins 1-2 of the PTT line or a ground on pin 1of PTT will cause Q* to start conducting and activate the TR relay.  (assuming the Hermes and the PA share a common ground.)

What do you all think?

[Evan Hand]

Patrick,

You are correct that grounding the PTT signal on the amp will turn it on.  If I am reading the HL2 schematic correctly, the PTT output of the HL2 is an N channel MOSFET that can handle 28 volts of Drain to Source.  As long as the power to the amp is below 28 volts, you should be OK.  A lower voltage is better.

73

Evan

AC9TU