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LF: Ultimate 2 or 3 as driver for external Class D

To: <rsgb_lf_group[email protected]>
Subject: LF: Ultimate 2 or 3 as driver for external Class D
From: "Dave G3WCB." <[email protected]>
Date: Fri, 4 Apr 2014 20:53:02 +0100
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Hi, Laurence.
Yep, done that. My U2 usually drives an outboard 20W 475 kHz PA in WSPR mode, and at the moment is driving a 180W PA on 137.500.
 
I leave the U2 PA in circuit, and feed it into a 50 attenuator to reduce the drive to the outboard PA. (My outboard PA has it's own driver, and only needs about 10dBm drive)
 
You can buy a 630m or 2200m plug in LPF from Hans Summers, or make your own, as I did. For a long time, the only LPF I had for my U2 was a 20m filter. I left this in circuit, and relied on the filter in the PA to remove any harmonics. The 20m LPF is completely transparent at 630m.
 
I've also rigged Send-Receive switching for my U2. The U2 processor keys a BS170, which is in series with the output BS170. You can use the same keying voltage to drive another BS170 that controls a Send-Receive or antenna changeover relay. It also switches the PA from "Standby" to "Send". The relay switches over with each of the QRSS symbols, which gets a bit noisy, but is fine for WSPR.
 
I've added a slight delay to my outboard PA so that the PA driver doesn't turn on for a few milliseconds after it is switched to "Send" by the U2. This removes the risk of the Send-Receive relay hot switching when there is RF present.
 
My 630m PA uses a single IRF540 in Class E, running from 13.6VDC, and is loosely based on one of Roger's designs. (GW3UEP). Efficiency and output could be improved by running it from 24VDC, but it's fine when running WSPR2 at 25W out.
 
There's a couple of pics of the U2 on my QRZ.com page.
 
Hope this helps!
 
73, Dave G3WCB IO91RM.
-----Original Message-----
From: [email protected] [mailto:[email protected]]On Behalf Of Laurence KL7 L
Sent: 04 April 2014 17:43
To: [email protected]
Subject: LF: XXM decode and Ultimate 2 or 3 as driver for external Class D

If anyone has successfully used a Ultimate 2 or 3 to drive an external 500kHz class D PA direct from the DDS outpins or via the BS170 (say into a TC4426 driving a IRF640) Id like to hear about any pit falls/expereinces before I let smoke escape :-)
 
with thanks
 
One lonely decode last night WG2XXM 475.712 -31 @1006Z on L400B/25ft @ 4600Kms  - sure was a noisy night. Nothing decoded non the NNE/SSW 1/4Y resonant loop - sometimes small is better :-)
 
Laurence KL7L WE2XPQ Alaska

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