Spectrain pre-drive info sought

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Spectrain pre-drive info sought

Post by radiogareth » Sat Jun 08, 2019 7:36 pm

After finding my Stealth Amp has possibly a mid-train device failure (N5, a bit odd but there's a lot less coming out than is going in!) I reached into the 'stores' and pulled out a Spectrain driver board. According to PyroJoe who sells these 10mW should see full output.
Using either my Pluto or Lime and 'various eBay' amps I can get as far as 0dbM which when fed to the SPectrian gives +30dBm as expected so the amp itself seems fine, I just need more drive.

So what sort of driver chain are people using to max this amp out for either NB or DATV?

Links, comments etc gratefully received..

Failing that, anyone know of suitable 2nd driver part (Labelled N5, the first in chain is labelled N4 and seems fine) to fix the Stealth amp?



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Re: Spectrain pre-drive info sought

Post by G4IUG » Sat Jun 08, 2019 10:22 pm

All I can say is that 10mW i/p gives 26W o/p unmodified.

Ex G6ANG/T and G8EAO

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Re: Spectrain pre-drive info sought

Post by DL4OCH » Sun Jun 09, 2019 10:49 pm


your issue seems to be common.
We have designed a pre-driver with approx. 37dB amplification and an output of max. 27 dBm out for DATV.
This should solve your issues, even with longer coaxial-cables.

If you can drive -10 dBm, you'll get 27dBm out. Enough to fiddle with low power.

Drop me a PM.

Best Wishes,
vy 73,
Wilm, DL4OCH

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Re: Spectrain pre-drive info sought

Post by 2i0jmt » Fri Jun 14, 2019 8:45 am


Just wondering, what eBay amps are you using and how many of each? I have a similar question but only for the "8W wifi amp"



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Re: Spectrain pre-drive info sought

Post by radiogareth » Fri Jun 14, 2019 8:01 pm

Hi Jonny, well I have a selection of things, some of them traceable to known devices and some not. Here is what I've found:
Search eBay for this "2MHz-700MHZ RF Amplifier Power Broadband For HF VHF UHF FM Transmitter Radio". For about £7.50 its got loads of gain up to 70cms then tails off but ideal for adding some poke to a Pluto either DATV or NB. I let the smoke out of mine when I was driving my Chinese MRF186 amp, mind you it went portsdown - amp - PA and hit 100+ watts....... briefly. Suspect the unshielded amp got back into everything at this level and sent it on its way. Too much gain for DATV on my amp anyway. It gets far too hot too but as far as I can tell that's mostly the regulator overhead burning off. Probably worth running it directly from 5 volts and bypassing the regulator altogether, then it might stay cool enough.
Next up are these "Low Noise LNA 0.05-4G NF=0.6dB RF amplifier FM HF VHF / UHF Ham Radio HighQ" or similar, they have got a bit more expensive recently but work well and have a named device SPF5189. I use these between Portsdown and various externals up to 13cm. I have one dead one, not sure what killed it but its on a nice board with SMA in and out and easy to replace with an active device, ones like are used in the Portsdown chain.
What works best for me is a nameless device that has clearly been re-worked on someone else's board and stuck in a small alloy box. This works best on 8.6 volts (gets hot above so suspect needless overhead again) up to and including 70cm and delivers clean power and decent gain. It wasn't so cheap but someone was using one at CAT18 and it worked well. Still listed, https://www.ebay.co.uk/itm/50-1200MHz-1 ... SwMmlbazre
Lastly I'm waiting on this from China https://www.ebay.co.uk/itm/TQP3M9009-50 ... 2749.l2649 once again a NAMED device with a great spec. Yet to arrive and be tested though.....
Hope that helps, I think they are ALL by-products of the cellular industry (?MODAMPS?) but cheap and ready built with SMA. Take the specs in the adverts with a pinch of salt and test for yourself. I'm still trying to convince myself which part is dead (or not) in the Stealth and how to bypass it without killing anything else. The drive seems to leak around devices making accurate measuring a bit tricky especiually as each stage seems to have attenuation after each amp.

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