The transmission over Qatar Oscar 100 satellite with SDR Console

L'amplification de signaux sur 2,4GHz

The amplification line

Now, I propose to focus on the transmission and amplification equipment, individually.

First element, the SDR transmitter

As indicated in the introduction, I only deal here with the case of an SDR transmitter. The power considerations obviously remain the same for a conventional up-converter transmitter.

LimeSDR mini

The LimeSDR is an open-source SDR receiver and transmitter USB stick, to be connected to a microcomputer, and covering frequencies from 10MHz to 3.5GHz (for the LimeSDR mini and LimeNET-Micro version) or from 100kHz to 3.8GHz (for the LimeSDR version) and operates in full duplex (simultaneous reception and transmission). Its maximum output power measured at the output of LimeSDR mini is 3 dBm (2mW).

Adalm Pluto Emetteur/Récepteur SDR

Other SDR transmitters / receivers are possible, such as Adalm Pluto from Analog Device (Amazon Link). A modification to improve stabilization is required for narrowband transmission (SSB). I invite you to refer to this modification of the Adalm Pluto of Lucien F1TE’s french article which concerns the replacement of the cristal by a TCXO whose temperature derivation is compensated. Another alternative is to provide a stable 40 MHz reference signal using a GPSDO (GPS disciplinated oscillator) generator

These SDR transmitters can be used for narrowband transmission but also as a broadband transmitter for DATV digital television (Maybe the subject of another article later ?).

Filtering

Before mentioning filters, I would like to recall some points of the regulations concerning the amateur band 2300 – 2450 Mhz. The amateur-satellite service may operate in the bands 435-438 MHz, 1260-1270 MHz, 2400- 2450 MHz, provided that this does not result in harmful interference to other user services. In these bands, the amateur service has a secondary status and any harmful interference caused by satellite emissions must be immediately eliminated (RR provision S5-282). As a reminder, the maximum transmitter output power is 120W (50.8dBm).

On the 2400 MHz band part, we will find public uses such as bluetooth and wireless networks Wifi 802.11b/g/n. It is therefore important that spurious emissions are properly rejected at low levels, and at least to those expected by the regulations [ APPENDIX 3 of the Radio Regulations for ground satellite stations: 43 + 10 log (P) or 60 dBc minimum]

It is therefore advisable not to drive the amplifier circuits into their non-linear operating area and to complete the stations, especially SDR, with a 2400 MHz band pass filter after the transmitter.

 

  1. A cheap filter exists on the Asian reseller market: the 2400 NMRF FBP-2400, with significant losses (4dBm) on 2400 Mhz and its Return Loss -20 dBm (SWR 1.2) Links. Links Aliexpress ou ebay.
  2. A second one is available in Canada, and sold by GPIO Labs: 2450 GPIO LABS. These losses are less significant (2.4dBm) for the same RL than the previous one. Link to Ebay.
  3. There are other more professional filters where losses are reduced:ID-Elektronik in Germany
  4. For do-it-yourselfers, there is a solution that consists in building a resonant cap “Pipe-cap filter”
The preamplification

Analog Device CN0417

On the diagram, after the transmitter, you will find a pre-amplification stage for the signal. In this diagram, it is a CN0417 board from Analog Device that is equipped with a two-stage, 1W, two-stage ADL5606 wideband amplifier (see ADL5606 datasheet), which operates over a frequency range from 1800 MHz to 2700 MHz. It integrates an in-line band-pass filter and will provide thanks to its real gain of 20 dB on 2400 MHz. It is powered by a micro-USB plug. Its maximum input level is 18 dBm.

SPF5189Z

 

Second possibility. The SPF5189Z is a 5V powered preamp that offers 8 to 11 dBm of gain. You will find a detailed measurement report on the Matthias DD1US website. My measurements give me 11 dBm of gain on 2400 MHz. According to the SPF5189z datasheet, the maximum acceptable input is 27 dBm. You can therefore completely cascade two preamplifiers, one after the other. The Chinese reseller market offers them for less than 5 EUR (link SPF5189Z Ebay, link SPF5189Z Aliexpress).

 

TQP7M9103 pour 2300-2400MHz

Alternatively, there are TQP7M9103 preamplifiers. Depending on the application diagram, you can expect 16 dBm of gain. A QORVO evaluation board exists for 2300-2400 MHz, with an announced gain of 16 dBm. However, this board is very expensive (Mouser USA). There are TQP7M9103 boards of Chinese origin (link Aliexpress 1, Link Aliexpress 2) at low prices, but it is not expected that they will gain on 2400 MHz. You will need to make the changes according to the application diagram for this frequency range. For amateurs, here is the Data Sheet of the Qorvo TQP3M9008 board (see page 16/25) and a link to DK5DN and DL5CN publications on the Amsat-DL forum showing the changes and their results. I have not personally tested the TQP7M9103.

Another alternative is the 2W amplification with the SKY66292-11 transistor. There is a SKY66292-11-EVB evaluation board (Mouser Link USA), which, like the previous amplifier, is offered at a rather high price (Here is the datasheet of the SKY66292_11_EVB board). An alternative is to make this amplifier using the diagrams put online by DB4UM on Github.

A last possibility (that I propose), is based on the Gali-84+ which proposes a gain of 17 dBm on 2400MHz with a maximum input of 0dBm (1mW). It is available on two kits from Minikits (Australia): Gali-84-R2 et Gali-84.

Remember to place an attenuator in front to ensure the maximum permissible input level (Link to attenuators Aliexpress).

The last stage amplification

After the first stage to bring your signal to more or less 200 mW (23 dBm), we can add a last stage of about ten dBm to bring your signal to 2.5 to 3 Watts.

There are two EDUP “booster wifi” amplifiers:

  • EDUP AB003, box labelled 8W : The gain of this amp (measured) is 14 dBm. The datasheet indicates a maximum level of 20 dBm signal at the input. Indeed, from 20dBm, the gain itself is reduced but the amplifier can still be used above it. The measurement curve below (red) shows that the gain is reduced to 7 dBm when attacked with 27 dBm at the input, the maximum reached being 35.3 dBm or 3.4 Watts (Link to Aliexpress, Ebay and Amazon)
  • EDUP AB007, box labelled 4W : The measurements show an almost identical gain, a little lower at 13 dBm. The maximum signal is 33.8 dBm, or 2.4W. The “4W” amp consumes 10W of electricity and operates nominally at constant RF power between 7.0V and 14V (I didn’t look for the maximum voltage). You can find this equipment on Aliexpress ou sur Ebay, et Amazon.

These two amplifiers are duplex wifi amplifiers (transmitter and receiver). We only need the emission amplifier part. The receiver preamplifier, which is active in stand-by mode, is automatically switched on when the input signal exceeds 3dBm when transmitting. Some publications propose to modify the amplifier so that the transmitter remains switched on. This modification is not necessary, as the switching is instantaneous and automatic, and does not bring any significant technical gain.

Intermediate power level after CN0417, after EDUP AB003, and EDUP “4W”

For amateurs who would have this need (DATV or small dish), there is also a 20W amplifier not personally tested but measured by DH2VA at a gain of 35dBm up to 15W (Link to  Aliexpress).