Re: [TowerTalk] MFJ-1025/1026

[Roger D Johnson <n1rj@adelphia.net>]

Tod - MN wrote:

> > 4.To protect the Aux Antenna input, it employs a internal, 
> > soldered in, 12v dial lamp as a "fuse". If you are the 
> > careless kind you may want to modify this  to avoid having to 
> > remove the unit from the case, unsolder the lamp and resolder 
> > in a new one if that terminal gets large input voltage from 
> > xmtr. Time consuming  if you are contesting or just DXing and 
> > the unit is the only reason you are  hearng the DX.
>
>
> I happen to have an MFJ-1026 and happen to have replaced the 12v dial light
> bulb fuse several times. Finally, I decided I should ground the AUX input
> whenever I was transmitting. I won't bore folks with the details, but I
> found that one can control an FET which handles the relay that does the
> grounding from the circuit point where the FET on the 1026 board controls
> the TX/RX relay for the MAIN inputs. Using an FET is necessary so that you
> don't load the existing circuit too much. Put the FET and the relay on a
> small prototype board and mount it near the AUX input. Wire length for the
> relay and FET is unimportant because you are dealing with control lines not
> RF lines. The leads from the relay to the AUX input and ground as best made
> short.
>
> One of the small, fast 12 volt SPST NC relays from DigiKey or others
> (costing about $3 + shipping) is quite adequate. To be really safe one wants
> to have the relay closed (grounded) when transmitting and also closed when
> there is no power to the MFJ-1026. Use the relay to ground the AUX input at
> the connector (leave the bulb fuse in place)and you will protect the LC
> filter at the AUX input.
>
> Folks who have this unit will have the schematic and can figure out what I
> wrote. Everyone else should simply hit the delete key.
>
> Tod, KØTO

On my FT-1000D, I broke the coax between TR circuitry and the receiver
and brought the ends out to a pair of RCA jacks on the back panel. I ran 
RG-58 from the jack connected to the TR circuitry to an external antenna 
switch for Beverages, etc. The pole of the switch goes to my preamp, 
through my MFJ-1025 and back to the RX input of the FT-1000. No worries 
about transmitting into the 1025 and easy to hook up external antennas.

73, Roger

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