For portable microwave operations, my station requires "smallish" 144MHz transceivers as the "tunable IF". I have previously used:
-IC275 (10 W version) - somewhat on the large size and heavy but an excellent performer
-FT290R Mk II- excellent also but has some drift issues and mode changing is "painful"
-TM255 A - Excellent radio for the purpose but mine recently "died
-"FT817ND - Very good for the purpose also, but the menu system can be "fiddly" and in addition this radio has more features and bands then required.
When on a "hilltop" it's nice to set up multiple dishes for the different bands that I operate (all bands through to 47 GHz) and it is nice to have a few "dedicated" tunable IFs so one isn't constantly changing these. Good IC202's and low power versions of the IC275 are hard to come buy and the price of multiple FT817s is somewhat prohibitive. I have been interested in SDRs for sometime and have built several Rx only versions of the "softrock" style SDRs. I had also been considering building a base transceiver based on the "UHF_SDR" project. However taking a computer out into the field to operate the "radio" was not a good solution to my need for small fully self contained 144MHz SSB transceivers.
When I was notified of the "SDR2GO" standalone controller for the UHF_SDR I decided this could satisfy my urge to build a tunable IF and decided to "have a go". The UHF_SDR + SDR2GO controller allows for a small SDR Tx/Rx package. All that was required was a few additional items to come up with a useful portable 144MHz transceiver:
-BPF (3 stage filter)
-Suitable PA (Mitsubishi 5W module Kit from "MINIKIT")
-Enclosure (made mine out of PCB stock with aluminium covers)
-Preamplifier (Kit from "MINIKITS")
-Interstage amplifier for Tx (ERA3 based)
-Rx / Tx switching
-Misc items.
Below are some photos of my build. For anyone contemplating such a project, an Internet search for UHF_SDR and SDR2GO will point you to ALL the required information. There is also a "yahoo group" for the UHF_SDR project and the SDR2GO controller resides on the "AQRP" forum.There is a lot of SMD soldering and some of the IC's to be soldered for the SDR2GO controller might be challenging for beginners. Anyone with appropriate soldering equipment a good set of magnifiers and some experience with SMD will find this project relatively easy. The documentation requires a little experience but is complete. Help from the forums is very forthcoming for those that need a question answered.It is also noteworthy that whilst I built my unit for 144MHz, this combination will also work at 432MHz for those wanting a 70cm "tunable IF".There is constant development by the developers and the software is user up-gradeable. As can be seen in the photos, there is no S meter and whilst I don't see this as a huge disadvantage for field microwave operations. I note that the developers have now implemented an add-on graphical display that shows absolute signal strength and a +/- 6kHz Panadapter!
MODIFICATIONS / ADDITIONS:
Initial testing showed that there was +17dBm of power from the UHF-SDR board at 144MHz but there was a lot of significant sideband leakage and other spurii. At much lower levels the signal was VERY clean with all spurii being down by 50dB or more. So it was decided to run the SDR at a much lower power level and use an "interstage " MMIC amplifier to bring the signal up to the desired level (and to limit it as well) to drive a Mitsubishi power module. An ERA 3 with suitable attenuators was used. A preamplifier was added because I used a three stage BPF that added significant loss ahead of the mixer. The NF of the base UHF_SDR is supposedly OK at 144MHz but I needed some gain ahead to overcome the switching and BPF losses. I decided that I would only need the "Adjustment Encoder" during initial set-up. As such i didn't include this in the front panel.
The audio out of the UHF_SDR is very low for driving a speaker but more than adequate for headphones. As such i added an audio amplifier to my unit to drive an internal speaker. The headphone connector is stereo whilst the internal speaker is for only a mono channel. I set my unit up for 3W output to be compatible with my portable microwave equipment.
INITIAL SETUP AND ON AIR TESTS:
A "signal Hound" spectrum analyser and tracking generator was used (itself an SDR based instrument) to align the transceiver. Adjustments / setup is required for:
-Rx levelsTx levels in SSB and CW
-Sideband rejection
-Phase and Amplitude adjustments for both Rx and Tx
The documentation on getting the SDR2GO aligned was excellent. Initial on air tests as a stand-alone transceiver were very good.
I'm looking forward to using my unit in the field. If you are looking for a 144MHz tunable IF then this type of build may be what your after!
