HF Transmitter #17 - RF Pre-Amp AGAIN and Performance Tests

Подписаться 3 тыс.

50% 1

OUCH!! I blew up the RF Preamp due to a dumb but yet commonly made oversight when building a push pull amp from BJT's. A quick fix later, I'm back in action and going through the CW power and spurious emissions tests.
No endorsement is made nor implied to any commercial products referenced in this episode.

Наука

Опубликовано:

7 авг 2024

Ссылка:

Скачать:

Готовим ссылку...

Добавить в:

Мой плейлист

Посмотреть позже

Комментарии : 5

@M0UAW_IO83 Год назад

I like this series, it's thoroughly enjoyable and informative. But, can I offer what I hope might be useful advice? You don't need a 1A diode at these power/bias current levels so changing it for a part with a smaller package, 1N914 for example, will help because it will react faster with less package to heat up. You almost definitely don't need to monitor both transistors because they share bias current and, if they're from the same batch, will be pretty closely matched but you do need the diode to be as closely thermally coupled to the transistor as possible, ideally in contact with the actual transistor if possible. I'd probably try and mount it to the black heatsink tab, either mechanically and with a dab of heatsink grease or glued with cyanoacrylate or epoxy, rather than in a chunk of aluminium Looking forward to the next in the series 🙂

@technishn Год назад

If you load the Si5351 with high impedance rather than 50 ohms then the even harmonics may be significantly reduced which should reduce even order spurs

@t1d100 Год назад

I am presently DIYing a demo board for the A model. If you decide to consider this chip, here are somethings to know. Even the brand name (AdaFruit) demo boards/modules are built with 25MHz pill-can reference oscillators. There are two problems with this oscillator - 1) They are significantly subject to thermal drift. 2) The 25MHz oscillator will not allow the chip to output some very particular RF frequencies, because of the way the chip multiplies and divides the reference oscillator. You need to use a 27MHz reference oscillator. See data sheet for allowed reference oscillator frequencies. The cure for the A model is to use a TCXO reference oscillator. But, the B model 5351 includes an internal VCO and it is not much more expensive than the A model. It may be cheaper to buy the B model, rather than the A model and a TCXO. The 5351 has a quirk on its reference oscillator pins. A TCXO is input only on its XA pin and, when used in this configuration, this pin is limited to 1V. Meaning, level shifting is likely needed. See DS Figure 6.6 and Table 13. Additionally: The AdaFruit module includes 5V/3V3 level shifters on the SDA and SCL lines, as they assume that you will power your Arduino with 5V. There is a trick to using an Arduino at 3V3 Vdd, which avoids needing the level shifting on these lines. Input 3V3 on the Arduino's 5V OUTPUT pin and it will run just fine. The 5V Output pin is connected after the Arduino's voltage regulator. See the 328P DS. HTH

@R2AUK Год назад

👍 ❤

@user-ij1lh4eb1e Год назад

Hello, my name is Sam. I designed a HF transmitter circuit. And I have a problem with the antenna that I explained in a video. Please let me know if you have a email address to send it to you. thank you Best regards