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Author Topic: Rx Signal Attenuates when amplifier is turned on  (Read 1941 times)
AB1PJ
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Posts: 33




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« on: May 28, 2012, 01:40:48 PM »

I have good Rx without the Ameritron 500 turned on using the remote control
When turn on the switch of the remote, the Rx signal attenuates by 30dB on 40m and
lower on lower bands.

I have checked all connections between radio and amp and tuner and antenna

Any suggestions?
thank you
jim
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AD6KA
Member

Posts: 2236




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« Reply #1 on: May 28, 2012, 01:51:14 PM »

Since it is band specific, maybe bad relay
contacts in the Low Pass Filter network?
Try cleaning those relay contacts??
73, Ken  AD6KA
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K1ZJH
Member

Posts: 949




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« Reply #2 on: May 28, 2012, 02:55:02 PM »

It sounds like you have a condition that is keying the amplifier continuously.

When the amp is OFF, the antenna change over relay is bypassing the amp and allowing the RX signals to pass
through.

If the relay is energized when the amp is turned on (which provides the keying voltage for the relay!!!!) you
will see a dramatic drop in signal strength if the relay is indeed being actuated during RX.


Pete
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AB1PJ
Member

Posts: 33




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« Reply #3 on: May 28, 2012, 03:27:42 PM »

Thanks Pete. That solved the problem.

I was sharing the relay keyeing line between the radio and the amp and an MFJ1026 Noise cancellation device
I basically made a Y cable from RCA cable and split the keyeing line between radio and 1026

Once i connected the radio relay out directly to the amp, the attenuation was gone, like you suggested.

Is there another way to do this i mean how to share the relay line between radio and two other devices such as an amp and a 1026?

thanks
jim
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K8AC
Member

Posts: 1465




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« Reply #4 on: May 28, 2012, 05:13:30 PM »

A power diode in each leg of the Y would isolate the two devices from each other.  Direction of diode depending on polarity of voltage being keyed.

73, K8AC
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KC4MOP
Member

Posts: 731




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« Reply #5 on: May 29, 2012, 03:41:11 AM »

A power diode in each leg of the Y would isolate the two devices from each other.  Direction of diode depending on polarity of voltage being keyed.

73, K8AC
I have been pretty lucky using a "Y" connector to share PTT around the shack. I do remember a similar situation with my station and I think I got out easy by reversing the key-up wires of the device that did not like the "Y".
And the diode approach might be a better engineering approach
Fred
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KM3F
Member

Posts: 501




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« Reply #6 on: May 29, 2012, 08:12:32 PM »

Anytime you try to share key up leads with multiple units this issue can arise.
Build a key up conroller or interface if you will, by using a separate relay to apply ground the the keying jacks' / cables' to the amplifiers.
In each line to the keying jacks use a diode so one unit does not back feed to another.
At Rat Shack, get a hobby housing, a strip of 4 RCA jacks or seperates, some diodes and terminal strips and a relay and your all set. You need to power the controller with 12 volts from some source and PTT switch it's ground to operate the relay the same as you would do directly to an amplifier..
You can even go with two sets of two or more if a relay is used with two sets of contacts that can ground each line set separately.
A controller like this can be expanded to handle any number of keying applications.
I control an AL80B, a 6m tube amplifier, two transverters and two solid state amplifiers using a 'collection key up' interface.
No 'equipment' keys unless you power it up and it's in XMT mode.
Good luck.
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