[hpsdr] Help with Alex SWR

[Graham / KE9H]

Don:

It sounds like you are fighting several problems.

Apparently you are trying to build an Alex from a bare board?

You seem to be having problems with both the low pass filters on 10 and 6
as well as the directional coupler.

For the purposes of all toroid windings, the definition of a "turn" is one
pass through the center of the toroid.  Any pass through the center hole 
is a turn.
Are your turn counts correct?

Do you have, or have access to, an antenna analyzer, like the MFJ-259 or 
similar/equivalent?

Did you use the exact part number for the detector diodes (D1 and D2), 
or substitute something else?

Did you use the exact part number for the 50 Ohm (actually 51.1 Ohm) 
resistors for the power bridge(R2 and R3)?
... or substitute something else?

Where did you get your toroids?  Are you using genuine MicroMetals and 
FairRite toroids, or did
you substitute something else? Or get a set of the Chinese toroids from 
TAPR?

What gauge wire did you use to wind your 10 Meter toroids?
... your 6 Meter toroids?
... your directional coupler toroid windings
... your directional coupler "staples" (single through toroid jumpers)?


73's,
--- Graham / KE9H

==

On 10/26/2013 9:42 AM, dlwaddel at netzero.net wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Help please!
>
> My Alex is reporting high SWR even though my external VSWR meter reports 1.0:1 VSWR into a dummy load.
>
> The history is that when trying to find why I lose 50% power on 6 meters when going through Alex, I discovered that I had wound T1 and T2 on the wrong core. I removed them and wound new T1 and T2 on the specified FT50-43 cores. Now Alex is reporting high SWR on all bands.
>
> Here are some specifics:
> 20 Meters
> Tune power level set to 50
> SWR in PowerSDR 1.7
> External meter SWR 1.0:1
> Jack J2 pin 2 reads 0.8 volts
> Jack J2 pin 3 reads 0.17 volts
> Forward power in PSDR 7 watts
> Forward power on external meter 50 watts
>
> 10 Meters
> Power level at 25
> SWR 47.7 in PSDR
> External meter SWR 1.0:1
> Jack J2 pin 2 0.4volts
> Jack J2 pin 3 0.4 volts
> Forward power in PSDR 3 watts
> Power on external meter 20 watts
>
> Before rewinding T1 and T2, high SWR was reported on 10 and 6 meters only. I had wound the originals on T50-10 cores. (Hey, they are both black.)
>
> T1 and T2 were wound with the same convention as other coils such that the leads are in the correct positions to mount on the board. I have inspected both numerous times and re-installed several times to make sure the problem isn't incorrect installation.
>
> Resistors appear to be correct values and the diodes are installed in the correct direction.
>
> The transmit seems to work fine on all bands into a dummy load with SWR protection turned off, except for losing about half the power on 6 meters and about 10 watts on 10 meters versus without Alex in the circuit.
>
> Don
> K3DLW
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