scannerrail
Member
Does anyone know where about where they are located and what they look like? I brought this cheap Handheld HT and I want to change the filter so it has a wide enough bandwidth.
IF filters in a handheld HT
- Thread starter scannerrail
- Start date
- Status
In general terms, the IF section is in between the RF and the AF section of the board. It's pretty hard to explain without a board/component layout. The IF filters look like a crystal can (HC33 or HC49 type), has that shiny chrome look but has 4 leads instead of the 2 leads that a crystal can has. Don't mistake these with the IF transformers, which are usually square in shape, in which the center has an adjustable ferrite slug that screws in/out. Unless you have the test equipment and alignment tools, don't be motivated to "tweek" those IF transformers or you may throw the whole IF line out of whack. These filters may have the KIVA brand name or an "FT-XXX" stamped on one side of the can. B e quick on removing or resoldering these units because they may be temperature sensitive.
Hi Scan and all,
Filters come in such a wide range of packaging it's impossible to describe them all and most closely resemble other components. I've not heard of an HT having user replaceable filters and monkeying around in one is MOST unwise. The IF selectivity skirt is already optimized for proper reception so even if you COULD identify the filters and get your fat fingers in there the only thing you could do is mess it all up. Always remember the very first rule of maintainence, if it ain't broke don't fix it.
Filters come in such a wide range of packaging it's impossible to describe them all and most closely resemble other components. I've not heard of an HT having user replaceable filters and monkeying around in one is MOST unwise. The IF selectivity skirt is already optimized for proper reception so even if you COULD identify the filters and get your fat fingers in there the only thing you could do is mess it all up. Always remember the very first rule of maintainence, if it ain't broke don't fix it.
N4JNW
Member
kb2vxa said:
Or, the Government's motto,
"If it ain't broke, fix it til' it is!!"
elk2370bruce
Member
Some old timers (and rabid tweakers) also believe that if you can open the case, you can "mod" it. If you have to ask how, especially with micro-miniature circuit boards, you'll kill your investment. Most scanners are already optimized so why tempt fate?
w0fg
Member
I don't believe the OP really understands what an IF filter is and does. It reads like he is expecting to be able to modify to scanner receive frequencies other than those for which it is designed. In any case, it ain't gonna happen.
scannerrail
Member
thats not what I need it for... I don't want to mod it for more frequencies I want it for a wider bandwidth since what I'm using for NOAA weather sats it's not going to be enough.. and since I only paid $50 for some Chinese HT I really don't care if it breaks or not.
wannabescannist
Member
How much bandwidth is needed? Aren't most IFs in the 10.7MHz or the 450s-470sKHz range?
scannerrail
Member
zz0468 said:
yeah might be another way..I would of brought another scanner but I was not going to spend $70 (what I saw was the cheapest on ebay) just to take apart and mod and it would not be usable for anything else like scanning.
wannabescannist said:
I think the bw is around 30 khz for the weather sats. Keep in mind, though, that there is doppler shift to contend with. Some, if not all, 137 MHz wx sat receivers use an even wider IF bw to allow the doppler shifted signal to remain inside the passband. One would either need to do that, or have some sort of AFC to keep the signal centered.
scannerrail
Member
zz0468 said:
I was expecting a drop in replacement on a Scanner or a higher cost Icom.. I was again expect to take out the soldering gun.
scannerrail
Member
This is what a person told me a week ago.
"You really don't have to tap the discriminator output to get wider bandwidth. One trick you can do to an old scanner you want to dedicate to wxsats is to remove the ceramic IF filter, and replace it with a .01uF ceramic disc capacitor. This will let pretty much all of the bandwidth through so you can properly decode the transmissions. I've never tried it, but I've read that it works OK. You can also buy a wider ceramic filter for it. I think DigiKey sells them. 99% of the inexpensive scanners use the little MuRata 10.7MHz IF filters, and since they're all the same size, you just have to find one that's wide enough, and swap it out. It ruins the scanner for another use, though, so don't expect to be able to monitor the police or taxis unless you don't mind listening to three channels at once!"
"You really don't have to tap the discriminator output to get wider bandwidth. One trick you can do to an old scanner you want to dedicate to wxsats is to remove the ceramic IF filter, and replace it with a .01uF ceramic disc capacitor. This will let pretty much all of the bandwidth through so you can properly decode the transmissions. I've never tried it, but I've read that it works OK. You can also buy a wider ceramic filter for it. I think DigiKey sells them. 99% of the inexpensive scanners use the little MuRata 10.7MHz IF filters, and since they're all the same size, you just have to find one that's wide enough, and swap it out. It ruins the scanner for another use, though, so don't expect to be able to monitor the police or taxis unless you don't mind listening to three channels at once!"
Tapping the discriminator does nothing to change the IF bandwidth, since it's already past the filters. You get unsquelched, un-deemphisized, unshaped audio. Yeah, replacing the filter with a cap *MAY* work, but then again, it may work very poorly. The filter is there because the radio NEEDS it. And not all filters are created the same size.
If SCANNERRAIL can post a crisp pic of the hand held circuit board it should be easy to ID the filter. I have swapped out dozens of IF filters for narrower versions on UHF radios operating on 12.5KHz splinter freqs and I have a drawer full of misc common IF filters for handhelds. If you swap same series filters there is no tuning needed.
prcguy
prcguy
Also - Digikey and Mouser used to sell common Murata IF filters.
scannerrail
Member
prcguy said:
I will post it when the radio arrives.
Hi again,
Skipping past the extraneous posts and getting right back to the point;
"...and since I only paid $50 for some Chinese HT I really don't care if it breaks or not."
That being the case I have a hammer you can borrow.
Skipping past the extraneous posts and getting right back to the point;
"...and since I only paid $50 for some Chinese HT I really don't care if it breaks or not."
That being the case I have a hammer you can borrow.
- Status
Similar threads
