Alternative to using 2n4427 for 1 watt drivers

[Albert H]

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.

[nrgkits.nz]

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

[Albert H]

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!

[rigmo]

2n3553 4-5W out (mrf237 any tray?)

[teckniqs]

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.

[rigmo]

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.

[Albert H]

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!

[radium98]

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

[rigmo]

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

[Albert H]

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).

[Bton-FM]

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’?

[teckniqs]

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

[Bton-FM]

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

[Albert H]

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

Here's my copy!

Book.jpg

[yellowbeard]

https://1lib.eu/book/1080423/019e52
Piracy! Yarr!

[reverend]

Has anyone tried the 2SC2851? These seem good for a Watt, though I would imagine they're more difficult to heatsink being a TO-92 package.

Rev

[Zozo]

Has anyone tried the 2SC2851? These seem good for a Watt, though I would imagine they're more difficult to heatsink being a TO-92 package.

Rev

Not tried one of those, I think you can get heatsinks for TO-92 case.

I've moved on now with my project, and gone with the MRF4427. After speaking with someone who uses them regularly, it seems they need very little to no heatsinking at all. They are so much more efficient compared to the 2n4427.

Sneak preview.

MK3+.JPG

[MiXiN]

https://1lib.eu/book/1080423/019e52
Piracy! Yarr!

Nice one fella.

I like reading now & again, but I like it even better when it's free.

[Bton-FM]

Has anyone tried the 2SC2851? These seem good for a Watt, though I would imagine they're more difficult to heatsink being a TO-92 package.

Rev

Not tried one of those, I think you can get heatsinks for TO-92 case.

I've moved on now with my project, and gone with the MRF4427. After speaking with someone who uses them regularly, it seems they need very little to no heatsinking at all. They are so much more efficient compared to the 2n4427.

Sneak preview.

MK3+.JPG

Why have you included the 2.2 Ohm resistor and 1nF capacitor to ground but then grounded all the other pins? Why don't you do away with the resistor and capacitor and connect the pin directly to ground like you have done with the other pins.

Also, the gain an order of magnitude better than the 2N4427! The datasheet specifies 18dB of gain @ 175MHz with 15mW input for 1 Watt out so the ~100mW out of the driver stage is going to be way too much. You could to add an attenuator between the 82pF capacitor after the transformer and the base of the MRF4427 or change the resistors around the MPSH10 so that it outputs less power.

[Zozo]

Has anyone tried the 2SC2851? These seem good for a Watt, though I would imagine they're more difficult to heatsink being a TO-92 package.

Rev

Not tried one of those, I think you can get heatsinks for TO-92 case.

I've moved on now with my project, and gone with the MRF4427. After speaking with someone who uses them regularly, it seems they need very little to no heatsinking at all. They are so much more efficient compared to the 2n4427.

Sneak preview.

MK3+.JPG

Why have you included the 2.2 Ohm resistor and 1nF capacitor to ground but then grounded all the other pins? Why don't you do away with the resistor and capacitor and connect the pin directly to ground like you have done with the other pins.

Also, the gain an order of magnitude better than the 2N4427! The datasheet specifies 18dB of gain @ 175MHz with 15mW input for 1 Watt out so the ~100mW out of the driver stage is going to be way too much. You could to add an attenuator between the 82pF capacitor after the transformer and the base of the MRF4427 or change the resistors around the MPSH10 so that it outputs less power.

I know what you mean in regards to the 2.2 ohm resister and bypass capacitor. All I've done at the moment is change out the 2n4427 for the MRF4427.

With the Rev 1a board I used for the first tests, I ended up with having to cut 1 track and introduce a resister. These mods have made there way over to the new revision boards which should be here on Tuesday next week. Once I've built one and tested it, I should finally and "hopefully" be able to say complete on that revision.

This newer revision is yet again another experiment, which I'm sure without doubt will require a track or two to be cut and the odd bodged in component in true "Dead Bug" fashion. I'll possibly just short out the 2.2 ohm and do away with the 1nf bypass, I may lose a few MRF4427's in the process as I play with the design. But the MRF4427 is a completely new animal to me, so it's all an uncharted area.

I know the datasheet can probably provide all the required information to develop a good working output circuit, however the results from the practical experiment will still need to be assessed.