1. Get the Best from your Masthead Preamp Ian White GM3SEK Click to view the slides

2. Masthead Preamps 1.Why use a preamp? What’s a preamp FOR ? Why at the masthead? Dynamic range – weak and strong signals How to optimize preamp gain 2.Making it practical All in one box, all on one board Weatherproof Cost-effective Nothing on the market  The DG8

3. What’s a preamp FOR ? “To boost signal strength”? “To overcome the noise”? “To make signals more readable”? To improve Signal-to-Noise Ratio Why Use a Masthead Preamp? NO. Getting warmer... Definitely NO!

4. Why Use a Masthead Preamp? Why at the masthead? To improve Signal-to-Noise Ratio - SNR is better than with a preamp in the shack (or the rig) - SNR is better than with the same preamp in the shack Why? - Because losses ahead of the preamp increase the system Noise Figure and decrease the SNR. - That loss of SNR can never be recovered...except by moving the preamp to the masthead.

5. Why Use a Masthead Preamp? Let’s run some numbers...

6. Why Use a Masthead Preamp? Let’s run some numbers... 1.Preamp in the Shack Transceiver 4.0dB NF Preamp 1.5dB NF High gain Cable 12m of RG213 1.0dB loss 4.0dB NFApproaching 1.5dB NF 2.5dB NF for the Receiving System Antenna

7. Why Use a Masthead Preamp? Let’s run some numbers... 2.Preamp AT THE MASTHEAD Transceiver 4.0dB NF Preamp 1.5dB NF High gain Cable 12m of RG213 1.0dB loss 4.0dB NF5.0dB NFApproaching 1.5dB NF for the Receiving System Antenna

8. Why Use a Masthead Preamp? For the lowest achievable Signal-to-Noise Ratio (always better than the same preamp in the shack) But that’s not the whole story...

9. Dynamic range – weak and strong signals Weak-signal performance is important ALL THE TIME “If all the DX is S9, you’re missing the Real DX!” In contests, the highest-scoring contacts are likely to be the weak ones. You never know if the next reply to your CQ call is going to be a weak one. But sometimes there are also extremely STRONG signals about You don’t want receiver overload to interfere with the weak signals

10. Dynamic range – weak and strong signals Too much preamp gain can CREATE receiver overload! Extremely high-gain preamps are a Bad Thing.

11. Dynamic range – weak and strong signals Effect of preamp gain Transceiver 4.0dB NF Preamp 1.5dB NF Gain: adjustable NF for the Receiving System Antenna

12. Dynamic range – weak and strong signals Effect of preamp gain

13. WEAK SIGNALS Dynamic range – weak and strong signals Effect of preamp gain

14. WEAK SIGNALS STRONG SIGNALS Dynamic range – weak and strong signals Effect of preamp gain

15. WEAK SIGNALS STRONG SIGNALS Dynamic range – weak and strong signals Effect of preamp gain

16. WEAK SIGNALS STRONG SIGNALS Dynamic range – weak and strong signals Optimum preamp gain is... The minimum gain that is absolutely necessary to get most of the possible SNR improvement. Every dB of un-needed preamp gain will also reduce the Dynamic Range by the same amount.

17. WEAK SIGNALS Dynamic range – weak and strong signals Effect of preamp gain

18. WEAK SIGNALS Dynamic range – weak and strong signals

19. Preamp Gain needs to be ADJUSTABLE. WEAK SIGNALS STRONG SIGNALS

20. Why Use a Masthead Preamp? For the lowest achievable Signal-to-Noise Ratio (always better than the same preamp in the shack) with smallest possible impact on Dynamic Range.

21. Masthead Preamps 1.Why use a preamp? What’s a preamp for ? Why at the masthead? Dynamic range – weak and strong signals How to optimize preamp gain 2.Making it practical All in one box, all on one board Weatherproof Cost-effective Nothing on the market  The DG8

22. Making it Practical Traditionally, masthead preamps have been: Expensive to buy Complicated to build Not very weatherproof Not very reliable. Not surprising that many people do without!

23. Making it Practical I wanted something that would be: High-performance Cost-effective Simple to build Weatherproof Reliable, so it’s always available when needed. Nothing on the market, so...

24. The DG8 2m Preamplifier High performance (RF front-end of G4DDK/G4SWX Anglian transverter) Integrated single-board design No expensive coax relays (ideas from muTek and HA8ET) Customized cable lengths for minimum RF losses. Proof against rain from all angles Optimized specifically for use at the masthead

25. The DG8 2m Preamplifier Performance Frequency range: 144-147MHz (bandpass filter) Noise Figure: 1.2-1.3dB typical (including relay losses) Gain: adjustable, 18dB to 11dB TX power handling: 500-750W (full carrier, JT65 duty cycle) TX VSWR: < 1.1

26. Weatherproofing Plastic box (IP65) so no leaks, no corrosion No exposed metal – once again, no corrosion Waterproof cable glands – no connectors. The DG8 2m Preamplifier

27. In short: a preamp that makes it easy to install in the right place – AT THE MASTHEAD.

28. Masthead Preamps 1.Why use a preamp? What’s a preamp for ? Why at the masthead? Dynamic range – weak and strong signals How to optimize preamp gain 2.Making it practical All in one box, all on one board Weatherproof Cost-effective Nothing on the market  The DG8

29. Masthead Preamps Three things to remember...

30. Masthead Preamps 1.The optimum location for a preamp is always AT THE MASTHEAD, as close as possible to the antenna. 2.Optimum preamp gain is the lowest level that will that will deliver most of the possible SNR improvement. 3.Every dB of un-needed preamp gain will subtract a dB from the Dynamic Range.

31. Get the Best from your Masthead Preamp Lots more information on my website: www.ifwtech.co.uk/g3sek