EMRFD Message Archive 10035

Message Date From Subject
10035 2014-05-18 21:01:17 Jason W6IEE 2.98 hexfet linear amp, what am I missing?
Finally got around to building one. However, attempting to drive it with various small 7Mhz transmitters with anywhere from 300 to 750 mW, I cannot get any signal out of it, or even into it, as it seems. Appears to present a horrendous mismatch to the exciting tx. I am using an IRF510 with an idling current of 100mA.

Any suggestions would be appreciated!

Thanks,
Jason W6IEE
10036 2014-05-19 11:32:02 Dana Myers Re: 2.98 hexfet linear amp, what am I missing?
10037 2014-05-19 11:47:28 Lasse Moell Re: 2.98 hexfet linear amp, what am I missing?
Figure 2.98 in EMRFD

Looks pretty simple to me, input load should be 50 ohm as there is a resisitor at the input and the gate would provide high impedance at these frequencies.

/Lasse SM5GLC

19 maj 2014, Dana Myers k6jq@comcast.net [emrfd] skrev:

 

10038 2014-05-19 12:56:55 Dana Myers Re: 2.98 hexfet linear amp, what am I missing?
10039 2014-05-19 13:36:39 Dana Myers Re: 2.98 hexfet linear amp, what am I missing?
10043 2014-05-20 11:23:09 victorkoren Re: 2.98 hexfet linear amp, what am I missing?
One thing you have to check is whether you connected the windings of the transformer at the right polarity.
If you start from the ground end the windings direction should be the same to thev other end, the output coaxial connector. Its a pity that the polarity of the windings are not marked in the schematics. (at least in my copy).
Did you adjusted the gate bias voltage to get 100 mA DC current without signal?
Victor - 4Z4ME