New builder question - amplifiers.

[M5TXJ]

Hi all,
Just built a Minitiouner and now started building a Portsdown, wondering what people use for amplifiers. I have RF concepts linears for 2m (170W) and 70cms (100W), both for 10W input. Obviously I'll need an amplifier between the Portsdown and these so looking for suggestions. A 23cms amplifier will be on the shopping list eventually but will have to wait at present.

73 Dave

[g8vpg]

Hello Dave,
What we call linear amplifiers for use with SSB voice transmissions are unlikely to be sufficiently linear for use with digital TV signals. I tried some BNOS 2m & 70cm amplifiers and they were terrible. Their lack of linearity caused the signal bandwidth to spread alarmingly, especially on 146.5MHz where we have a very narrow band to use.
For digital TV use, a Class A linear amplifier is required. You can tell these because they draw a heavy bias current and get warm even when they are not being driven. Even then, they have to be severely de-rated from their standard ratings for digital TV applications; for example, the commonly used Mitsubishi block for 2m is rated at 60W, but is really only good for 10W TV duty.
You can buy these ready made from the German manufacturers such as Kuhne or DG0VE, or buy kits from Minikits in Australia. Also have a look at G4DDK's website, where he sells boards for use with the Mitsubishi power amplifier modules.
73 Shaun G8VPG.

[M5TXJ]

Thanks Shaun, I should have stated in my first post that I intend to modify the amplifiers to be suitable for DATV, I was planning (or hoping for) 15-20W but even for that I'll need 1-2W of drive. I wasn't sure if an RA07H4047M would be linear enough at those levels. Thanks for the advice, I'm sure I'll need lots!

73 Dave