Alternative to using 2n4427 for 1 watt drivers

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Albert H
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Re: Alternative to using 2n4427 for 1 watt drivers

Post by Albert H » Sat Jun 13, 2020 12:33 am

BFS22A is a great little transistor. At 12V, you get exactly 1 Watt out for 80 mW in. In my broadband circuit, it gives a perfect 72Ω match at 1 Watt.
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Re: Alternative to using 2n4427 for 1 watt drivers

Post by nrgkits.nz » Sat Jun 13, 2020 12:39 pm

Albert H wrote:
Sat Jun 13, 2020 12:33 am
BFS22A is a great little transistor. At 12V, you get exactly 1 Watt out for 80 mW in. In my broadband circuit, it gives a perfect 72Ω match at 1 Watt.
That would be excellent for a link using tv coax into tv yagi’s

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Re: Alternative to using 2n4427 for 1 watt drivers

Post by Albert H » Sun Jun 14, 2020 2:35 am

Exactly! We still use UHF STLs. I just did a system that's concealed in the vestigial sideband of a local TV station! The customer's station is "quasi-legal", and they don't want their studio found. A combination of microwave and UHF got their STL requirements nicely sorted. The microwave stuff is spread spectrum PCM, so just looks like digital hash to the casual observer.

Until we supplied their new system, they were using a weird Band 1 set-up which worked in "burst mode". They'd send ~1 hour of programme as a short burst of data over about 90 seconds. The link transmitter had white noise modulating the baseband, with a subcarrier at 60 kHz that actually carried the data. The link receiver had a demodulator using a PLL to recover the data, then the logic fed a 4GB RAM module that the audio was assembled on to. This system was pretty secure, but was only capable of mono, and the audio bandwidth was limited to about 8kHz - not really "hi-fi".

The new system gives them full broadcast bandwidth stereo, and operates in "real time" allowing properly "live" programmes. The path length is only 5 km, but it's through a busy city, so it has to robustly ignore noise and interference. The UHF portion is really difficult to track because of the field strength of the TV station - when I did a similar trick in the 1980s, Gotts couldn't understand why he couldn't find the link frequency!

Covert link systems are great fun to design and implement. They're also good for studio security!
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Re: Alternative to using 2n4427 for 1 watt drivers

Post by rigmo » Fri Jun 26, 2020 8:53 pm

2n3553 4-5W out (mrf237 any tray?)
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Re: Alternative to using 2n4427 for 1 watt drivers

Post by teckniqs » Fri Jun 26, 2020 8:59 pm

MRF237 connects up slightly different to the 2n3553, the collector and emitter connection points are the opposite way around.

....That is why on the old RDVV boards they had 2 holes drilled in to connect the base for output device, one hole at the front and one at the back, depending on what way the transistor connects up. :tup

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Re: Alternative to using 2n4427 for 1 watt drivers

Post by rigmo » Fri Jun 26, 2020 9:22 pm

teckniqs wrote:
Fri Jun 26, 2020 8:59 pm
MRF237 connects up slightly different to the 2n3553, the collector and emitter connection points are the opposite way around.

....That is why on the old RDVV boards they had 2 holes drilled in to connect the base for output device, one hole at the front and one at the back, depending on what way the transistor connects up. :tup
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Re: Alternative to using 2n4427 for 1 watt drivers

Post by Albert H » Sat Jun 27, 2020 2:36 pm

Don't connect that mess to an aerial! There will be generous amounts of harmonic energy. There will also be spurs at the crystal frequency either side of the carrier - probably on an inconvenient frequency!
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Re: Alternative to using 2n4427 for 1 watt drivers

Post by radium98 » Sat Jun 27, 2020 8:52 pm

Albert H is wright in his answer.terrible harmonics and spurs will be spread .

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Re: Alternative to using 2n4427 for 1 watt drivers

Post by rigmo » Sun Jun 28, 2020 12:43 pm

sure albert and radium but im interested for final stage of 2n3553 and matching....

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Re: Alternative to using 2n4427 for 1 watt drivers

Post by Albert H » Mon Jun 29, 2020 4:26 am

It's NOT the way to do it!

Get Bostian, Raab & Krause's wonderful "Semiconductor RF Power" book. It gives you all the formulae and the principles you should follow when designing a PA stage. You'll need some mathematical ability (and if you haven't got mathematical ability, you should forget engineering and take up needlepoint or something).
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Re: Alternative to using 2n4427 for 1 watt drivers

Post by Bton-FM » Mon Jun 29, 2020 10:16 am

Albert H wrote:
Mon Jun 29, 2020 4:26 am
It's NOT the way to do it!

Get Bostian, Raab & Krause's wonderful "Semiconductor RF Power" book. It gives you all the formulae and the principles you should follow when designing a PA stage. You'll need some mathematical ability (and if you haven't got mathematical ability, you should forget engineering and take up needlepoint or something).
Are you sure it’s called ‘semiconductor RF power I could only find a book by all 3 of them called ‘solidstate radio engineering’?

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Re: Alternative to using 2n4427 for 1 watt drivers

Post by teckniqs » Mon Jun 29, 2020 10:42 am

Bton-FM wrote:
Mon Jun 29, 2020 10:16 am
Albert H wrote:
Mon Jun 29, 2020 4:26 am
It's NOT the way to do it!

Get Bostian, Raab & Krause's wonderful "Semiconductor RF Power" book. It gives you all the formulae and the principles you should follow when designing a PA stage. You'll need some mathematical ability (and if you haven't got mathematical ability, you should forget engineering and take up needlepoint or something).
Are you sure it’s called ‘semiconductor RF power I could only find a book by all 3 of them called ‘solidstate radio engineering’?
https://books.google.co.uk/books?id=HrD ... er&f=false

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Re: Alternative to using 2n4427 for 1 watt drivers

Post by Bton-FM » Mon Jun 29, 2020 11:02 am

teckniqs wrote:
Mon Jun 29, 2020 10:42 am
Bton-FM wrote:
Mon Jun 29, 2020 10:16 am
Albert H wrote:
Mon Jun 29, 2020 4:26 am
It's NOT the way to do it!

Get Bostian, Raab & Krause's wonderful "Semiconductor RF Power" book. It gives you all the formulae and the principles you should follow when designing a PA stage. You'll need some mathematical ability (and if you haven't got mathematical ability, you should forget engineering and take up needlepoint or something).
Are you sure it’s called ‘semiconductor RF power I could only find a book by all 3 of them called ‘solidstate radio engineering’?
https://books.google.co.uk/books?id=HrD ... er&f=false
thanks :tup

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Re: Alternative to using 2n4427 for 1 watt drivers

Post by Albert H » Tue Jun 30, 2020 2:22 am

My ageing memory... You're right. It's "Solid State Radio Engineering".

Here's my copy!
Book.jpg
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Re: Alternative to using 2n4427 for 1 watt drivers

Post by yellowbeard » Tue Jun 30, 2020 6:01 am


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