Help with Biophone MCI 3550-12 Not Receiving Transmissions

[chas3]

I just picked up a Medical Communications and Instrumentation Inc Paramedic Biophone almost identical to the picture that I posted. Unit did not include the battery pack, which I know would be toast at this point, so I have run a 13.8V power supply into it.

It turns on and transmits on all 10 channels (463/468 mhz duplex), that can be heard on my scanner, however when using another radio to transmit to it you can hear the mic being keyed on both the handset and built-in speaker, but no voice can be heard. Squelch is all the way down and background static can be heard. Tone switch is set to off.

Any ideas?

Obviously I am not familiar with how this unit operates and any help with documentation and/ or where to buy a battery housing would be greatly appreciated.

Thanks!

 

[WA0CBW]

Are you testing with both radios in the same room? You may be desensing the Biophone.
BB

 

[chas3]

Yes I am. I will try to move farther away and see if anything changes. Thank you.

 

[ecps92]

The Biophone transmits on 468 and receives on 463
on your test radio are you transmitting on 463? and do you have the correct PL/CTCSS??

I just picked up a Medical Communications and Instrumentation Inc Paramedic Biophone almost identical to the picture that I posted. Unit did not include the battery pack, which I know would be toast at this point, so I have run a 13.8V power supply into it.

It turns on and transmits on all 10 channels (463/468 mhz duplex), that can be heard on my scanner, however when using another radio to transmit to it you can hear the mic being keyed on both the handset and built-in speaker, but no voice can be heard. Squelch is all the way down and background static can be heard. Tone switch is set to off.

Any ideas?

Obviously I am not familiar with how this unit operates and any help with documentation and/ or where to buy a battery housing would be greatly appreciated.

Thanks!

 

[chas3]

The Biophone transmits on 468 and receives on 463
on your test radio are you transmitting on 463? and do you have the correct PL/CTCSS??

Yes, I am transmitting on the correct receiving frequency for the Biophone, but have no idea if it has a coded squelch. How can I determine that?

Like I said, the "tone" switch is set to off, but I'm not certain if that switch is for a receiving or transmitting tone?

 

[ecps92]

Scanner with Tone Search/Find or Auto should provide you with the tone to attempt

Yes, I am transmitting on the correct receiving frequency for the Biophone, but have no idea if it has a coded squelch. How can I determine that?

Like I said, the "tone" switch is set to off, but I'm not certain if that switch is for a receiving or transmitting tone?

 

[chas3]

Scanner with Tone Search/Find or Auto should provide you with the tone to attempt

I was using the "close call" feature on my scanner to see if the Biophone was sending a tone during transmission (it was not). How would I use the scanner to see if the Biophone is looking for a tone when receiving?
Sorry for my simplistic questions. I'm just not as educated in radios as many of you are.

 

[ecps92]

Been so long since I used CC but that radio did not show tones, only freqs.

Program in the scanner the Freq and see what tone it is transmitting, then you can use that tone in your Transmitter to see if it opens the squelch

I was using the "close call" feature on my scanner to see if the Biophone was sending a tone during transmission (it was not). How would I use the scanner to see if the Biophone is looking for a tone when receiving?
Sorry for my simplistic questions. I'm just not as educated in radios as many of you are.

 

[ladn]

It turns on and transmits on all 10 channels (463/468 mhz duplex), that can be heard on my scanner, however when using another radio to transmit to it you can hear the mic being keyed on both the handset and built-in speaker, but no voice can be heard. Squelch is all the way down and background static can be heard. Tone switch is set to off.

I'm not the radio police, but it's important to mention that your test transmissions could cause interference to medical facilities within range of the radios.

Consider using a dummy load on the Biophone (it will radiate a very short distance) and either a dummy load or the very lowest power setting on your test radio.

 

[jeepsandradios]

Those are public safety frequencies. You can't just use it to talk on. What is the plan for this ? The MED channel list is common across the US. As said you should be on a dummy load and not transmitting in the wild on that.

 

[chas3]

Understood. I plan to pull out the TX & RX modules to see if there are crystals that can be replaced to make it GMRS. I didn't even expect it to work when I purchased it. It's more of a conversation piece.

 

[speedway_navigator]

but have no idea if it has a coded squelch. How can I determine that?

A Jetstream JTFR1 will show freq and CTCSS tones but not digital codes.
I don't think they are made anymore, quick search only shows expired ebay listings.

 

[joshlober]

The amplifier and duplexer are specific to the factory frequencies. So, even if you could change the TX and RX frequencies, you'd also need to address those items.
The Tone RX switch is strictly receive tones. Transmit tones are controlled by the rotary knob.
There is no digital squelch. The was an ANI option for sending a fast DTMF sequence to alarm your 'home' hospital. I believe this is located in the 'Tone Pack' module.

 

[BMDaug]

Yes, I am transmitting on the correct receiving frequency for the Biophone, but have no idea if it has a coded squelch. How can I determine that?

Like I said, the "tone" switch is set to off, but I'm not certain if that switch is for a receiving or transmitting tone?

I have one of these… it was $60. It has a bnc port and comes with a bnc antenna. It is a frequency counter and displays ctcss or dcs along with signal strength. Wide frequency range, analog and DMR, usb charging and inexpensive… you just tx for a second or two and it’ll display all pertinent info.

-B

 

[joshlober]

@chas3 I have the full service and maintenance manual for this unit. Let me know if you still need assistance.
Josh

 

[prcguy]

You said the squelch is all the way down and background noise can be heard, that means its running in noise squelch mode and should receive anything on its frequency. If not something is broken.

 

[hfd376]

So the radio is transmitting, but not getting any audio? I would check to see if it's set up to send a ekg. I think these muted the handset audio so it wouldn't corrupt the ekg.

 

[joshlober]

Here are images and videos from my Biocom 3550 restoration project:

Biocom 3550

56 new items · Album by Josh Lober

photos.app.goo.gl

 

[joshlober]

Here is a video of a fully restored and operational Biocom 3550-12:

New video by Josh Lober

photos.app.goo.gl

This one will be donated to LA County Fire Museum (HOME - Los Angeles County Fire Museum). If you have access to other Biocom 3550 or 3502 radios, and want to sell or donate it for restoration and museum donation, please contact me.
Josh

 

[joshlober]

Today I finished the restoration of the Biocom 3550-12 which was donated by Kevin Nida at the FirstNet Authority.
The unit is now fully functional and has been installed in a NOS (new old stock) case.
The next phase of the project is restoration of the Rapid Charger unit and batteries.
If anyone has a 3550 they are willing to sell or donate, please contact me. I still have some NOS components and there are EMS museums that want these added to their collections.
Thanks,
Josh