Hello Jim, the previous owner removed the HT choke!
These sidebands are as expected for a 3PH 6 pulse capacitor smoothed supply.
The original choke is on its way here which will improve things by 20dB or so.
I even ran some SPICE simulations which was a nice reminder of exactly what is
going on. So, no great mystery after all. I will report the improvement.
I have must have always had these sidebands. It is only because they are
visible on FT8 on 144MHz and above, due to the low noise floor and high station
density in NW EU. This is why my attention was drawn to the 'problem'. As Bob
AH7I pointed out at 1KW out the sidebands are 10mW, so I will continue to use
the amp until the choke arrives.
73
Conrad PA5Y
________________________________
From: Amps <amps-bounces@contesting.com> on behalf of Jim <jimw7ry@gmail.com>
Sent: 26 May 2021 03:25
To: amps@contesting.com <amps@contesting.com>
Subject: Re: [Amps] 300Hz sidebands
What about a different amplifier power supply.
What about a different supply (or battery) for the exciter?
Thanks
73
Jim W7RY
On 5/24/2021 1:09 PM, Conrad PA5Y wrote:
> Hello Geert.
>
> Yes, I did try 3 different drivers, and several amplifiers off this HT
> supply. The same result.
>
> K3S>transverter>driver amp> PA
> TS2000
> IC746
>
> Same result.
>
> I eventually got the supply out of the rack and took the lid off. The reason
> for the sidebands was quite obvious, a previous owner had removed the HT
> choke, I also tested the 8uF cap, it was 7.85uF my DER EE DE 5000 LCR meter.
> The original choke will be sent to me this week. These sidebands have been
> there for the 5 years that I have run this amp.
>
> Regards
>
> Conrad PA5Y
>
> -----Original Message-----
> From: Amps <amps-bounces@contesting.com> On Behalf Of Geert Jan de Groot
> Sent: 24 May 2021 19:53
> To: amps@contesting.com
> Subject: Re: [Amps] 300Hz sidebands
>
> On 23/05/2021 20:52, amps-request@contesting.com wrote:
>> I have several tetrode amplifiers that run from a 3PH 50Hz supply. With the
>> advent of the FT8 I have become aware that I have 300Hz sidebands at only
>> -50dBc, this is obviously unacceptable.
> Apologies for asking, but have you tried a different driver transceiver to
> see if the signal (level and/or frequency) changes?
>
> Geert Jan
>
>
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