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Sunday, 22 June 2014

History Repeating....

Well,

I've bought myself a new RSGB book; it's called "Building a Transciever" and is actually a reprint of a load of RadCom Homebrew columns. Those of you been here a while may remember I actually made the exciter from these articles a while ago back hare:

http://g0mgx.blogspot.co.uk/2010/11/radcom-dec-2010-ssb-exciter.html

Now, there has been a lot going on here since then and I probably have a bit more experience in these matters, so, to cut a long story short, I am planning to start again from scratch and have a go at the books contents.

The book itself is here:

http://www.rsgbshop.org/acatalog/Online_Catalogue_What_s_New_26.html

and the authors website is here:

http://homepage.tinet.ie/~ei9gq/

So, today I have made the exciter (again):


I could be a bit critical of this book (well actually I am and have told the RSGB so), here's why:


  • The photos in the book are exceptionally small (even compared to the original magazine copy)
  • They are black and white making component identification impossible in some cases
  • Some of the book schematics dont have all the component values in th picture or the text (crystal frequencies for the SSB exciter oscillator and also the Op-Amp in the Mic amp) - and that's just so far
Here's the output of my exciter on LSB with a 2KHz audio signal injected into the Mic amp and the carrier adjusted for what I think will be about right. Each of the SA images includes a sweep of the crystal filter - I have no real idea why the top of the passband has appeared to be so wibbly wobbly - could it be an impedance thing? The filter is 450 ohm ish and the SA is 50 - but I doubt it somehow.


I've used a GQRP club SSB filter 10.7MHz and the two carrier crystals that match it; however, my USB carrier point was **way** too high in frequency so I have had to add an inductor into the circuit to pull the crystal downwards (this is why I would like to know what frequency crystals the author used). Here's the exciter in USB:



Also the output of my oscillator is no where near the amplitude the author suggests he had from his. We will see.

Here's another shot showing the actual frequencies of my USB and LSB carriers:


I used a TL072 op-amp in the mic amp and here are the gain figures I measured:


So, all in all a good start I think.

Here's the latest two additions to the household (the dogs not the wife - she has been around for quite a while):



Good, egh?

3 comments:

  1. Hi,
    Nice comment in liter vein, (the dogs not the wife - she has been around for quite a while)

    I have been a fan of many designs of ei9gq. it is lovely that this designs come up again. All the best to you and Emon Skelton (ei9gq)

    ReplyDelete
  2. dear sir,
    Can you please try TL072 instead of 082 for lower noise as it is Mic pre-amplifier?

    ReplyDelete
    Replies
    1. Ah, my error - I did use a 072, just typed it in wrong!

      73s

      Delete