Distored audio from RM Station 550 Base amp.

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minon
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Distored audio from RM Station 550 Base amp.

Post by minon » 08 Aug 2018, 10:22

Hi Guys,

I have a head scratcher here for me and not sure what exactly is going on.

First off all the equipment I am using:

1.) Ranger RCI-2970 N2
2.) RM Station 550 Base linear.
3.) MFJ- 826B SWR/Watt Metre
4.) President Himalaya WB antenna mounted at 35 feet from the ground.

What I am currently doing:

1.) Ranger’s power is turned down to 4 Watts for FM / and between 12 and 15 Watts for SSB
2.) The Ranger is running from a 50 Amp PSU also.
3.) The mic gain is also set to around 45 to 50%
4.) On SSB on setting 6 of the amplifier the Amp is putting out around 550 Watts PEP and on setting 1 around 90 Watts PEP
5.) My antenna’s SWR through the 11 Metre band is no higher than 1.2, even when driving the amp.
What results I am getting:

1.) On FM the audio is perfect and the 4 Watts produces around 200 Watts.
2.) On SSB on any setting from 1 to 6 the audio sounds narrow, scratchy and distorted, I am using a friends stream around 5 miles away to test.
3.) I have checked coax, patch cables, made sure there is no RF coming back into the shack etc. and even switched over to the G5RV and the results are the same.

The RM Station 550 is mint and practically brand new as is the ranger and also the SS9900 I have tried with it.

Could the amp be faulty or what could be the issue, as I am out of ideas?
Thanks

Robbie

Tim
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Re: Distored audio from RM Station 550 Base amp.

Post by Tim » 08 Aug 2018, 11:19

firstly, make sure that the linear is getting enough power input, a full 12V and the power cable is at least 17A rating. secondly remove every other box of tricks between radio and linear and keep all coax cables as short as possible, thirdly try the linear in SSB with 10W output from the radio, you could be over driving it, if it still distorts reduce the radio power output until the audio is clear, if none of the above clears it then the linear is either faulty, you have RF issues or it's just not compatible with your equipment.

minon
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Re: Distored audio from RM Station 550 Base amp.

Post by minon » 08 Aug 2018, 13:11

Thanks Tim but this is a base amp so has a built in PSU.

The equipment in my shack is also heavily grounded, I am almost thinking it could be an ALC issue but will have to check when I am home.

Usually I would drive it with around 10 Watts or even less, but from searching it seems these amps are not great on SSB from all accounts.

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Re: Distored audio from RM Station 550 Base amp.

Post by Tim » 08 Aug 2018, 14:43

I bought a brand new RM KL503 last year, the newest type with silver heatsink and blue controls/switches and that one had a very sticky relay which was causing a very similar fault, I sent it back.

minon
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Re: Distored audio from RM Station 550 Base amp.

Post by minon » 08 Aug 2018, 16:50

Tim wrote:
08 Aug 2018, 14:43
I bought a brand new RM KL503 last year, the newest type with silver heatsink and blue controls/switches and that one had a very sticky relay which was causing a very similar fault, I sent it back.

Mmmmmm you could be onto something there, tried it with my 7300 with the ALC at 30% Mic Gain at 15% and Power at 10 Watts and it was brutal.

So that well could be a possiblity.

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ch25
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Re: Distored audio from RM Station 550 Base amp.

Post by ch25 » 08 Aug 2018, 17:49

You have a problem with common mode current. Chris
You can't have too many antennas...

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cb4ever104
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Re: Distored audio from RM Station 550 Base amp.

Post by cb4ever104 » 08 Aug 2018, 18:31

ch25 wrote:
08 Aug 2018, 17:49
You have a problem with common mode current. Chris
I had that problem which was driving the relay in my BV135 a bit loopy Chris . Changed the patch lead , and problem solved .
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Re: Distored audio from RM Station 550 Base amp.

Post by minon » 08 Aug 2018, 18:44

How do you mean common mode current.

As for all the patch leads all are brand new and testing fine on the multimeter.

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radio pete
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Re: Distored audio from RM Station 550 Base amp.

Post by radio pete » 08 Aug 2018, 21:26

There is a bias mod you can do,~~~ or as I did a new mains Tranformer, Bridge rectifier 50A & a full regulated supply @14.5volts works well on SSB

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Re: Distored audio from RM Station 550 Base amp.

Post by cb4ever104 » 09 Aug 2018, 08:34

minon wrote:
08 Aug 2018, 18:44
How do you mean common mode current.

As for all the patch leads all are brand new and testing fine on the multimeter.
RF flying around the shack . From my experience , it's the length of the patch lead that can cause issues . Sometimes changing one for one that's longer , or shorter can cure this issue .

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Re: Distored audio from RM Station 550 Base amp.

Post by ch25 » 09 Aug 2018, 15:18

What about transmitting on dummy load? Is it distorted too?
Chris
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minon
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Re: Distored audio from RM Station 550 Base amp.

Post by minon » 10 Aug 2018, 09:38

I have since returned the amp but thank you all for your help and advice.

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Re: Distored audio from RM Station 550 Base amp.

Post by wa10 » 16 Aug 2018, 09:25

RM station 550's have a design fault in the bias switching circuit, bias does not turn on at low drive ssb audio keeps dropping in & out of class C & sounds scratchy.
i posted a simple mod om here & wwrf that cures it.

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