In regard to MaxTrac 800 ceramic filters

[Josh]

I know there are two filters in the MaxTrac radio, but specifically what are they for? Is one for RX, and the other for TX or is one low pass and the other high pass to keep things within rated RX specs?

I ask this because I think my radio is getting desensed. I have the filters removed and I am monitoring 896 and 897Mhz frequencies (yes, I know they aren't 902 ham, but close, right?)

I think I am getting desensed from 852Mhz frequencies, as 942 doesn't seem likely.

Even if I were to get a pair of Muratas at this stage of the game, I think they'd roll off too much down at 896Mhz.

Input appreciated.

-josh

[W6JK]

They're band pass filters, and they're in the receiver. You probably haven't messed with the ones in the IF, so for the front end you need a pair of Toko #6DFB-902E-10, covering 890 to 915 MHz. These would be a good choice tor an amateur repeater receiver too, since they're centered on 902.5 MHz.

'JK

[Josh]

Ok, I'll see if I can get them.

Without the filters, here's what I'm seeing in terms of data receiving.

I can be right next to the transmitter (by that I mean about 100' from the tower itself) and I can get it with the maxtrac without errors with no antenna on the radio, or a short piece of wire coming out of it.

Hook an external antenna to it, and I can no longer do it, but a site about a mile away comes in consistently, but it also did with the piece of wire as an antenna.

I don't audibly hear any difference, I don't notice any desense from the image frequency, but apparently it's there enough to cause enough of an error to void the packet stream.

Is my radio cracked out, or will these 915Mhz filters do the job and possibly eliminate the problem?

[W6JK]

It it's so touchy that you can't hear the difference between working and not working, maybe the audio level going into the packet modem isn't quite right. I'd try making small adjustments there to see if it gets better or worse.

Without the filters, the front end of the receiver is wide open to all and sundry signals across a wide spectrum. The offending signal needn't be on the image (you'd hear it if it was). It could be almost anywhere.

'JK

[Josh]

It it's so touchy that you can't hear the difference between working and not working, maybe the audio level going into the packet modem isn't quite right. I'd try making small adjustments there to see if it gets better or worse.

Without the filters, the front end of the receiver is wide open to all and sundry signals across a wide spectrum. The offending signal needn't be on the image (you'd hear it if it was). It could be almost anywhere.

'JK

idk what its deal is. It works sometimes ok, and others like absolute crap. I have a GTX900 for 935 stuff (which is in band) it works great for data RX using the flat-unmuted audio line.

The 800Mhz MaxTrash running nearly 30Mhz out of band, but in a way which should work, gets me a lot of errors sometimes, but not others. I don't audibly notice anything wrong with the signal, and the audio levels, while higher than the GTX, have been compensated for to give me good audio levels into the computer for decoding...

Maybe it's the radio....

-Josh

[pjbaron]

They're band pass filters, and they're in the receiver. You probably haven't messed with the ones in the IF, so for the front end you need a pair of Toko #6DFB-902E-10, covering 890 to 915 MHz. These would be a good choice tor an amateur repeater receiver too, since they're centered on 902.5 MHz.

'JK

I am looking for a source of these Toko Filters preferably in the US, having difficulty finding them.

Please advise, thank you. Pete N2ISY

[W6JK]

I am looking for a source of these Toko Filters preferably in the US, having difficulty finding them.

Please advise, thank you. Pete N2ISY

Digikey has the surface mount version - 4DFB-902E-10.

You probably could figure out a way to mount them in place of the through hole parts.

'JK