Experimenting with an SDR on a military radio
Browsing bands with a military radio is not as simple as it is with commercial radios. In the best case scenario you will have to go up and down using decade switches or pressing keys. There are even some radios like the Thomson TRC-3400 or the PRC-319 that need the exact frequency to be entered. Here is when a receiver comes in handy but then, you have to think about sharing an antenna, or use two, taking care not to fry the receiver. This MFJ 1708 will allow you to protect your receiver by switching antennas automatically.
Of course you could take an IF signal to the SDR so you can see what the transceiver sees, but if you have more than 1 radio, the task would be not feasible.
I have found some issues with the transmission leaking into the SDR receiver. Some audio can leak into the microphone and cause feedback. There is a Mute connector on the MFJ but I don’t know how it can be used to cut off the audio from the receiver.
What do you think?
PS sorry I said mfg instead of MFJ 😅
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Comparing the circuit diagrams in the manuals for the 1708 and the current model 1708B a lot more components have been added to improve isolation of the SDR receiver when the transmitter is active, so I dont think your experience is new. The mute output in the original MFJ-1708-SDR is a relay contact that is grounded when the receiver is connected. The later MFJ-1708B-SDR has internal jumpers allowing the mute relay to be grounded either during TX or RX. Either way the SDR needs to have a mute/unmute input or you need to have an external relay or gated amplifier between the SDR and a separate speaker.
It's a very good idea.... But I didn't get where the RFI comes out? From the SDR or from the Rx/TX? When out of SDR, then I would say volume of SDR to 0 and it's good
@Radiogenes
10 ай бұрын
The problem is that when sdr antenna is on, the antenna for the transceiver is off. So only one signal is “on”. So you can’t use the audio ok the transceiver because its antenna is off the circuit except when it is on tx mode…
Hi, great addon to station, I've have mfj (the only one with rf issue, sometime) - elad - and a chinese one, the Elad was the best and in the middle price, the cheap chinese do the work but at 144 mhz not so good, my next try will be a new chinese one but with swr meter (dont mind for me) who can rx in both radio at same time (with 3db loss) mfj work 0-450, elad 0-160 chinese the same like elad ...73 de iz3qvb
Hola Diogenes! Perdona mi confusion. O sea, estas recibiendo con un SDR y transmitiendo con el radio militar? O el SDR esta recibiendo la señal del radio militar? Lo lindo de tener un gran radio militar es usar el radio para recibir tambien pienso yo hihi .. logico, entiendo las dificultades y limitaciones tambien y imagino que esto es lo que estas mostrando. Al igual que gente que usan un 7300 solo para transmitir y el receptor es un SDR. Y claro despues la pregunta que tengo es sobre el standalone portapak. Primera vez que lo veo. Si compras el portapak no necisitas un SDR como SDR Uno/ RTL dongle etc?
@Radiogenes
10 ай бұрын
Es solo un experimento. Pero es un hecho wue muchos de nosotros para buscar frecuencias que están en uso usamos un segundo receptor. Algunas radios militares requieren de introducir la frecuencia directamente y eso ralentiza mucho la búsqueda. Usar la misma antena es lo complicado y por eso este conmutador de antena automático resuelve este problema. El hackrf es un sdr muy interesante porque no solo reecibe sino que también tiene la capacidad de transmitir en un rango muy elevado de frecuencias… 1Mhz hasta 2500 o más