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Author Topic: 1 HF radio 2 amps  (Read 3791 times)
WY7CHY
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Posts: 1016




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« on: February 05, 2018, 08:12:45 AM »

Does anyone think there's a problem with hooking up 1 radio, with a 2-1 antenna switch to 2 different amplifiers. (Of course, I'd also have a 2-1 switch for the Send/PTT cable too).

I figure with the antenna switch, and the power OFF to the unused amp, there shouldn't be a problem. I have a solid state home brew amp that is around 350-400 watts. I also have an 800 watt amp. (Usually running around 700 watts). The solid state is convenient; no tuning required; etc. Good for MOST times when a little extra power is needed. 5-6db gain. The big amp requires tuning; but is nice when I need a lot more power. 8-9db gain.

Electrically; I know that it is totally fine. I'm just wondering if anyone has ever experienced any issues. I can't imagine any, but that's why I ask.

Thanks. Mike
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W8JX
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Posts: 13268




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« Reply #1 on: February 05, 2018, 08:21:51 AM »

You have to switch amp input AND amp output....
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Ham since 1969....  Old School 20wpm REAL Extra Class..
WY7CHY
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Posts: 1016




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« Reply #2 on: February 05, 2018, 09:22:06 AM »

My amps already go to a switch. Multi-Radio / Multi-Antenna.

Currently, I have 1 radio on 1 amp; and a 2nd radio on the 2nd amp. Outputs of the amps go to the multi equipment/antenna switch. I want to reconfigure things around and ONLY USE the one transceiver. But I want to keep the 2 amps.

On a side note; with only one amp POWERED UP at a time; do I need an actual switch for the PTT/SEND (RCA Cable); or can I just use a "Y-Splitter" for the RCA. With only 1 amp POWERED UP at a time, there's no chance of KEYING BOTH amps at the same time.

Thoughts?

Thanks. Mike
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W8JX
Member

Posts: 13268




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« Reply #3 on: February 05, 2018, 09:36:03 AM »


On a side note; with only one amp POWERED UP at a time; do I need an actual switch for the PTT/SEND (RCA Cable); or can I just use a "Y-Splitter" for the RCA. With only 1 amp POWERED UP at a time, there's no chance of KEYING BOTH amps at the same time.


Typically when you key a amp you are just grounding a low voltage DC line to key amp. It "should" be okay but it would not hurt to put a blocking diode in each PPT line going to amp to prevent keying voltage from one amp entering the other. Unlike tying PTT amp connections on multiple rigs that have no voltage of their one on circuit, a amp does.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
WY7CHY
Member

Posts: 1016




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« Reply #4 on: February 05, 2018, 10:06:06 AM »

Thanks JX.

But being the 2nd amp would be powered off; and because the transmitter is completing the circuit (Ground) for the PTT voltage coming from the "Hot Amp"; the voltage shouldn't have any reason to go to the 2nd amp.

With that in mind, I think I probably have a bunch of small video (RCA) switches in my junk box somewhere. Before the days of HDMI; where everything, composite, component, etc. was RCA. I could use one of those if need be.

Thanks. Mike
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
W8JX
Member

Posts: 13268




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« Reply #5 on: February 05, 2018, 10:19:38 AM »


But being the 2nd amp would be powered off; and because the transmitter is completing the circuit (Ground) for the PTT voltage coming from the "Hot Amp"; the voltage shouldn't have any reason to go to the 2nd amp.


But before you actually key amp it has voltage on that line and if paralleled with other amp that will place voltage on its keying line connection. It may not be a problem for other amp but a blocking diode will remove doubt.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
AA4PB
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Posts: 15065




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« Reply #6 on: February 05, 2018, 10:27:06 AM »

With the PTT circuits wired together (no switch), when the PTT is not keyed then the powered amp will be feeding voltage back into the amp that is not powered. What that does will depend on the design of the keying circuits in both amps. One possibility could be that the unpowered amp will leak enough current to ground to cause the powered amp to remain keyed all the time. Again, it all depends on the design of the amp. The safe solution is either a SPDT switch or a diode in each amp PTT line (anode side to the amp) in order to prevent the flow of current between amps.
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Bob  AA4PB
Garrisonville, VA
WY7CHY
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Posts: 1016




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« Reply #7 on: February 05, 2018, 11:05:13 AM »

Excellent points on both sides.

Like I mentioned, in my junk box, I know I have some old RCA switches for switching composite/component audio/video before the days of HDMI. One of those will work fine. They switch BOTH Positive and Negative so there's complete isolation.

Thanks. Mike
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
N1UK
Member

Posts: 2242




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« Reply #8 on: February 05, 2018, 11:27:28 AM »

I found a cheap multiplex pcb on ebay.  Something like this.

https://www.ebay.com/itm/1-Piece-8-Channel-Relay-Module-Optocoupler-Isolated-Relay-for-Arduino-Blue/332403059947?epid=5006637938&hash=item4d64c42ceb:g:dkIAAOSwEkhZ0wLi


I used 2 Ameritron 5 channel remote coaxial relay boxes to switch the amp inputs and outputs.  Everything it driven from one Ameritron control box and can switch up to 5 amps to one transceiver.


Mark N1UK

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W1VT
Member

Posts: 3395




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« Reply #9 on: February 05, 2018, 11:51:47 AM »

You never really know what is inside with an old Heathkit unless you open it up and look.  And just to be sure, look at it on an oscilloscope and measure the PTT line just to be sure the voltage is what you think it is.  Even if someone did carefully document what he did, that documentation may have gotten separated.

Zak W1VT
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WY7CHY
Member

Posts: 1016




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« Reply #10 on: February 05, 2018, 12:51:14 PM »

"Heathkit"Huh Where did that come from?

Modern, LOW VOLTAGE amps. Nothing special. Normal 12vdc relay type.

Anyway; I'll be using an AV switch. PCB types look cool, but way too complicated. I can burn 1.3 calories flipping 2 switches. One for the coax to the amp and one for the RCA relay to the amp.

Thanks. Mike
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
AA2UK
Member

Posts: 920




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« Reply #11 on: February 05, 2018, 01:21:51 PM »

Well a Heathkit even some of the older tube amps can try and pull a high current AC relay to ground not good for a solid state rig isolated by an AV switch. The rig needs to enable a low voltage relay, the contact closure (amp keying) needs an isolated contact closure.
Bill, AA2UK
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WY7CHY
Member

Posts: 1016




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« Reply #12 on: February 05, 2018, 01:39:25 PM »

Still have no idea what you or VT is trying to say.

I'm well aware of some of the high draw/voltage amps. E.g. I had a Kenwood TL-922A. They draw a lot. Too much for MOST solid state transceivers to handle. (Except for many of the Kenwoods that saw that coming)

Dealing with normal amps with 12vdc, 100ma low current requirements. My radios are already connected to these amps. They have no problem. An AV RCA switch will isolate the 2 amps PTT no problem.

PB and JX brought up the one concern. Voltage from the hot amp going into the cold amp with a "Y-Splitter" Cable. Definitely a concern I hadn't thought of. But an AV switch will work just fine isolating the PTT 12vdc relays from the 2 amps.

Thanks. Mike
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Born Wild - Raised Proud: 73
Cheyenne, Wyoming
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