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Author Topic: LuLu Style Tx's 10W carrier, 40W Peak, with Modulator, Mod Tranny + 6925 XTAL  (Read 13646 times)

Offline ThaDood

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When I noticed some FM on the Radio Systems, I Am Radio (a.k.a. updated Talking House), TX, I grounded the case of the main crystal to chassis ground and that reduced the FM to better than 1/2 of what it was. The 13.560MHz AM Pixie-like TX I have, the main crystal is 13.560MHz (Thank you Fearless Fred on that one!). That crystal is also tied to chassis ground. On FM listening, I really have to crank the volume all the way to just hear it. It's better than any commercial AM TX gear that I have. You might want to give that I try. Where did I get the idea from? Before ICF (International Crystal Manufacturer.), closed up, I asked their engineers if that was a good practice to ground crystal cases, and they recommend that indeed. 
From DC to light, I take a huge spectrum bite!

Offline Stretchyman

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It's grounded already. I've already explained the fming is due to an inductor used to pull the Xtal L.F.

All future LuLus will use an AD9833, hopefully immune from any fming issues.

The end!

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Offline Stretchyman

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Just add a final (final!) note on the fming issue.

I have invested in an 8902A and can measure the fming, distortion, power, Freq and +/- mod level.

The fming issue is only present at mod levels exceeding 100%.

The mod level on the Tx is set by a control on the front panel. This does NOT adj the power and WILL cause distortion, fming of the carrier and causing the mod amp to cut out as it has a built in DC detectior to protect itself, if it is set too high.

The ONLY real way to monitor this with a scope initially and making sure ALL audio material NEVER exceeds a level that causes the mod level to exceed 100%.

To make sure your audio is LOUD it will need to be compressed. We're NOT talking MP3 compression here but 'audio compression' which raises the average level so everything is LOUD! Simple to achieve with pre recorded material as there's a wealth of software out there. However if you're running live you will need a decent audio compressor/limiter. I'm not going to go on about which one is best but you can spend $1000's on a real good one! However doing this with software on prerecorded material costs nothing!

If you'd like any more info please PM me.....

Str.
'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

Great discounts on ALL my transmitters if purchased via HFUnderground


                                              ;)

Offline syfr

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These Re fine transmitters and Stretchy is the man!!
NRD525/TenTec Paragon lotsa wires and some beams