Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Old March 3rd 19, 01:03 PM posted to rec.radio.amateur.moderated,rec.radio.amateur.homebrew,uk.radio.amateur,free.uk.amateur-radio
external usenet poster
 
First recorded activity by RadioBanter: May 2018
Posts: 15
Default [M1GEO] 2.4 GHz TX with LimeSDR & EDUP WiFi PA


George Smart - M1GEO

///////////////////////////////////////////
2.4 GHz TX with LimeSDR & EDUP WiFi PA

Posted: 02 Mar 2019 04:29 PM PST
https://www.george-smart.co.uk/2019/03/limesdr-edup-pa/



Following on from my Receiving EsHail-2 GeoSat article, the obvious next
thing to write something about transmitting. I created a draft of this
article, but it seemed to mix heavily with the specifics of my station and
was less generic. So I felt it better to create this page first, detailing
my 2.4 GHz transmitting station, which I have just cobbled together in the
time since writing the original article.



About the LimeSDR




Let me first start by saying that Ill be using a LimeSDR USB which has a
continuous frequency range of 100 kHz to 3.8 GHz. Clearly acceptable for
our requirements of 2.4 GHz. The bandwidth the SDR can support is
staggering 61.44 MHz. The SDR is based around an Altera Cyclone IV FPGA
with 256 MB of DDR2 RAM and a Rakon RPT7050A reference clock at 30.72 MHz.
It has 6 inputs and 4 outputs, and boasts a CW transmitter power of up to
+10 dBm (10 mW).



The RF sockets on the LimeSDRClock and USB sockets on the LimeSDR




Clearly the LimeSDR is nothing without some fancy software to drive it; and
there are plenty of good offerings. I decided to opt for SDRConsole V3 by
Simon Brown G4ELI, which at the time of writing was version 3.0.5 (Feb
2019).



SDRConsole with the LimeSDR




The process of setting the LimeSDR up was easy. I had to collect the
LimeSDR drivers for Windows and install those. That process is nicely
described on the Miriad RF LimeSDR USB Driver Install page, but the crux of
it is: (a) download the drivers from their GitHub page [direct link to
master here], (b) use Device Manager to find the LimeSDR, and replace the
driver with that in the zip.




Once the driver is installed, youre ready to set up SDRConsole. When the
program starts, it will state that you do not have any radios defined, and
give you the opportunity to define one. Simply select Search and then
LimeSDR and it will find your radio. Accept the changes youve made.



Radio Definitions: Define your LimeSDR




Once you have defined your radio, you should select it from the box that
pops up following the definition (and subsequently each time you start
SDRConsole). Select the LimeSDR you have just defined, make sure you select
a bandwidth that supports transmitting (TX) in the Bandwidth option, and
Start will become clickable in the bottom left. You should see the console
spring to life.



Select Radio: Make sure you select a bandwidth what supports TX.




From the Receiving EsHail-2 GeoSat article, you will recall that the
narrowband transponder input is 2400.050 MHz to 2400.300 MHz. Taking the
middle of this band to be 2400.175 MHz. The screenshot below shows the
radio on this frequency. I have put boxes and tails on some of the
important settings.








From the figure above, you can see the receive frequency on the top left
box, with the transmit frequency on the top right box. The Sync RX options
for frequency and mode show that the TX frequency and more are locked to
that of the receiver.




The Drive control on the top right box controls the RF power on the output
and we shall try to characterise that later. Just above it is a TX button
which causes the transmitter system to be engaged, and the receiver to be
muted.




Finally, in the bottom left there are controls which select which of the
LimeSDRs 6 receive sockets and 4 transmit sockets are in use.



LimeSDR Output Power




The next thing to do is measure the LimeSDRs TX power on the frequency of
interest: 2400.175 MHz, the centre of the NB transponder uplink. A CW
signal is used to generate a constant power level.




To achieve this, I have used a known calibrated R&S NRP18A, which will
measure power from 100 pW to 200 mW. We are expecting a maximum of 10 mW,
so we should be easily safe to use this.




The drive level is a percentage, ranging from 0 to 100. My basic plan was
to take a reading every 10%, and if there is a large non-linearity, Ill
take further measurements in those areas. At this point, the LimeSDR is
only powered via the USB bus, and has no external power source. With drive
levels below 50%, the reading was noisy, so I concentrated on the linear
part of the curve.



Drive Level (%)Power (dBm)Power
(mW)50-41.620.00006960-34.350.00036770-26.50.00223980-18.310.01475790-9.690.107399100-1.620.688652



Graph of LimeSDR output power vs drive level at 2400.175 MHz



EDUP 8W WiFi Power Amplifier




I purchased an EDUP 8W WiFi power amplifier for £35 in February 2019 for
use with the LimeSDR and EsHail-2 uplink. There had been talk on Twitter of
these amplifiers being suitable, so I decided to give one a go.



EDUP 8W WiFi Amplifier cost around £35 delivered




Without getting into details, the amplifier has a system which detects if
the WiFi radio is transmitting, and enables the PAs TX path, or if the
radio is receiving, and enables a separate RX path. This is exactly like
VOX on an amateur radio amplifier. However, since the packets are very
short on WiFi, with guard times in the order of 400 nanoseconds, the hang
time is very short, and thus not suitable for SSB. We thus need to modify
this behaviour, so that the amplifier is in TX all of the time, or, even
better, when the LimeSDR is transmitting perhaps using a GPIO pin to drive
the amplifier but thats unimportant for now.



PTT Modification: EDUP 8W Amplifier




Heres a snap of the insides of the amplifier. Its clear that there is some
room for improvement in gain with this amplifier, such as removing the
(likely lossy) TX/RX switching, etc., as we dont need these parts. However,
for now, well leave it. Swapping the RF-OUT RP-SMA connector for a standard
SMA connector is probably a wise decision for the radio amateur.



Inside the EDUP 8W WiFi Amplifier




The mod, in its basic form, is just a solder bridge across pins 4 (VS) and
5 (+IN2) of the ADA4851-4 quad rail-to-rail op-amp on the opposite corner
of the board to the DC power socket. The mod makes it appear that the diode
detector is detecting a huge signal (5.787 V, the supply rail). The
reference voltage (-IN2) is set at 0.189 V. When the voltage at +IN2
exceeds -IN2, the device enters transmit mode.



Before modAfter mod




If the amplifier is in receive mode, the status LED illuminates red.
Conversely, if the amplifier is in transmit mode, the status LED
illuminates green.



Measurements with the EDUP Amplifier




In terms of the experiment, the EDUP amplifier input is connected with an
SMA barrel to the LimeSDR output, and the EDUP amplifier output is
connected (via RP-SMA on the included short RG174 patch cable) to a 20 dB
attenuator which in turn connects to the power meter.




Using this configuration, I do not expect that the output power will be
come very high, since their is not enough drive level from the LimeSDR at
−1.62 dBm. I see about 13 dB of gain, with an output of around +11dB
(~10mW) of RF output power.




At this point the EDUP amplifier is drive limited. Working backwards, to
achieve a theoretical +39 dBm (8 W) output, we would need to input +26 dBm
(0.4 W) input.




The amplifier draws around 170 mA in receive, and about 380 mA in transmit
with no RF (just quiescent bias).



More Gain!




Clearly connecting the EDUP directly to the LimeSDR does not provide enough
power. There is a need for some more gain. Looking around what options are
available cheaply, you quickly come across some options.



Qorvo SPF5189Z



SPF5189Z breakout module available from eBay, AliExpress, etc.




The Qorvo SPF5189Z has a small signal gain of 11.9 dB at 2.2 GHz (the
closest listed frequency to the required 2.4 GHz) and an output P1dB of
22.7 dBm. This output power is close to the 26 dBm input required for the
EDUP, although it is not recommended to run the system close to the 1 dB
compression point (P1dB). With the SPF5189Z in line, we see approximately
20 dBm output (100 mW) from the EDUP.




Adding another SPF5189Z following the first gives around 30 dBm (1 W).
Adding another 10 dB of gain early on in the drive chain will get us closer
to the goal of 8 W output, but the system was becoming unwieldy and would
probably not be suitable for use on air without inter-stage filtering as
the parts used are wide-band.



Analog Devices CN0417 Evaluation Board



Analog Devices CN0417 Evaluation Board (bottom side) [source]




Another part brought to my attention by @Manawyrm on Twitter is the Analog
Devices CN0417 evaluation board (EVAL-CN0417-EBZ). It is a USB Powered 2.4
GHz RF Power Amplifier, and can be purchased for around £26 ($35 USD).




I have not used this part yet, but I know that others have with some
success. The EVAL-CN0417-EBZ is based on the ADL5606 is a broadband,
two-stage, 1 W RF driver amplifier which operates over a frequency range of
1800 MHz to 2700 MHz.



Nearly there




With some tidying of the interconnects, I was able to get to 32.98 dBm
(1.95 W). More filtering will be required before letting this loose on air.



Screenshot of SDRConsole with RF Power Meter inset. +32.89 dBm = 1.95 W



Getting it on air!




At this point I was pretty keen to see if I could make it to the EsHail-2
satellite. The day I tried, 2 March 2019, followed an announcement by AMSAT
that the narrowband transponder gain had been reduced, so I was keen to



AMSAT-DL reduced the transponder gain by several decibels on 28/02/2019




Using a WA5VJB quad-patch antenna purchased from Sam G4DDK, I was able to
get going sooner than if I had held out to wait for the dual-feed solution
that Mike G0MJW and others had been working on. The patch can be seen
connected to the amplifier with a simple SMA barrel connector.



Patch antenna and EDUP PA




Balancing the amplifier and patch antenna on the back of a large reclining
chair in the garden, I was able to align the patch antenna to the
satellites location. Setting the TX frequency of the LimeSDR to the centre
of the transponder band (2400.175 MHz), with an output power of around 1W
of I was able to hear a single tone through the EsHail-2 narrowband
transponder, I quickly added a CW paddle and was able to confirm my signal
by sending M1GEO TEST several times, listening via the BATC NB WebSDR as
discussed in my Receiving EsHail-2 GeoSat article.




I took a short recording using the BATC WebSDR:



M1GEO TEST received at BATC Goonhilly Web SDR



Some filtering?




W1GHZ has a nice study on pipe-cap filters and there are other articles
that describe their construction such as KO4BB Pipe Cap Filters
construction page. Other options include inter-digital filters and similar.




Not much to report here I still have some experimentation to do.



Where next?




The next article in this set describes making a dual-band feed. It is still
being written

This posting includes a media file:
https://www.george-smart.co.uk/wordp...89674.0kHz.mp3

Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
[M1GEO] Receiving EsHail-2 GeoSat M1GEO via rec.radio.amateur.moderated Admin Homebrew 0 February 21st 19 01:43 PM
[M1GEO] Operating as G3PYE/M M1GEO via rec.radio.amateur.moderated Admin Equipment 0 May 12th 18 02:29 PM
WIFI DJboutit Equipment 0 September 1st 04 01:30 AM
WIFI DJboutit Equipment 0 September 1st 04 01:30 AM
WIFI DJboutit Equipment 0 September 1st 04 01:30 AM


All times are GMT +1. The time now is 02:56 AM.

Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 RadioBanter.
The comments are property of their posters.
 

About Us

"It's about Radio"

 

Copyright © 2017