IF filters in a handheld HT

[obijohn]

Gentlemen: Let us not forget that most FM radio receivers have TWO i.f. sections. For the purpose of this thread let us disregard the first i.f., and consider the 2nd i.f...The 2nd i.f. is most likely where you will encounter the Murata filters. they will be located in close proximity to the quadrature detector i.c., and the 2 nd i.f. oscillator crystal.

This will be the final determinant of what will pass for recovered audio. In my experience-you need something between 30-60 KHz. of bandwidth to make GOES satellite receivers work well.

I know of no manufacturer that makes a filter that passes that bandwidth. So, the .01 capacitor might be the answer. the question is-do you install it in place of the 1st i.f., or the 2nd i.f.?

I believe that you will want to do this at the 2nd i.f. if you are going to use a capacitor in place of the filter.

I have never researched this, but there surely are people who make receivers for this application. A Google search might be a good thing to do.

Have fun, and good luck. Be sure to report back with your results!

 

[Big_Ears]

A chinese HT. Hmmm, I'm wondering if it's a bootleg copy of someother radio manufacturer. Lately, they have been masters on copying and remanufacturing software and electronic items. I wouldn't be suprised if it looks like another manufacturer's model. One model that pops up in my mind would be the Ranger, 1 W, 3 channel, mini H/T, programmed for business itenerant frequencies. It might even have a crystal controlled TX/RX.

 

[scannerrail]

Radio came today and I forgot to charge my battery pack for my DSLR

and wow this thing is much smaller then it looks in the pictures.

 

[scannerrail]

pictures...

I can't split the board without having to desolder 2 pins that hold the top PCB to the lower part.. maybe when it cools down this afternoon I will fire up the iron.

 

[scannerrail]

More

Lower part of PCB



Upper part

 

[obijohn]

The little bit of the owners manual I saw under the pictures was impressive. The English was actually understandable and grammatical !. It looks to me that this thing was developed just for the U.S. E-Bay market. Most impressive. I am sure that everyone monitoring this thread will be anxious to hear how well it works for you.

P.S. I am curious about the battery pack. That will be a give away of what was copied, or if it is an original product.

More info about that would be appreciated by many of us here.

 

[scannerrail]

LOL the manual is a joke... it's a direct Chinese to English translation.. As soon as you open it up you can tell whats ahead..

"It uses lock cirtle frequency compose technology"

LOL and what it was resting on what a manual I found on the internet where someone of English decent did the painstaking job of translating it the correct way.

I've already drilled a hole in the case because it had no hole over the mic and it makes your voice muffled.

The battey pack or so I heard is listed as Ni-Cd but it really has Ni-Mh AAA cells inside. It's a clip on and is sitting in the charger as I speak.

From what I also heard it's modeled off one of the Kenwood model's I can't remember off hand.

found what the inside of the battery pack looks like

http://www.kg4ivd.com/index.php/Jing_Tong_Pictures

Ah it's a Kenwood TH-22AT clone

 

[Bill_White]

Hey, thats not a bad looking little radio.
Where did you get it??
It would make for a nice portable APRS station..

 

[scannerrail]

Hey, thats not a bad looking little radio.
Where did you get it??
It would make for a nice portable APRS station..

http://stores.ebay.com/radiofactoryhongkongsuppliers

good seller sent a message telling me it shipped and gave me the tracking number along with it.

only thing annoying is the 2.5mm jack it uses over a 3.5mm jack..

And funny thing is (I have to wait for the sat to pass over again) I was unable to get NOAA 15 with my Radio Shack PRO-95 but I heard the tail end of it on the Ebay radio, which I thought was kinda shocking.. but it's a bit more smaller to carry around if your just going to grab NOAA sat signals.

Not much is on the VHF band at least that I know of...

 

[prcguy]

Ha, a Jingtong! Those are not type accepted for sale in the US and people have been fined by the FCC for importing and selling them. A friend bought a bunch in VHF and UHF and I think there’s one lost in my garage somewhere. You were originally asking about widening the receive BW and the IF filter that is determining the final BW is the black cube between your thumb and index finger that says W55B. It looks like a 455KHz Murata CFWLA series and the 6dB BW is +/- 15KHz. This is about the widest offered in this series. The silver crystal looking thing next to your index finger is the 21.4MHz first IF filter and I am not familiar with the mfr. The “F” may indicate the BW and with Murata’s nomenclature it would be +/- 6KHz, which is probably not right. The first IF filter is usually a bit wider than the final 455KHz filter. You may be better off removing the black filter and bridging it with maybe a .01uf ceramic cap and let the first IF filter determine the BW. Hopefully it will be wide enough for your satellite project.
prcguy

 

[scannerrail]

Yeah I was very aware of that.. I was not using it to transmit in the first place and it was cheaper then getting another scanner..

NOAA 18 is passing over head now.. from what it seems the Jingtone might be a little bit better picking up the signal then my Radio Shack Pro 95.. I'm waiting as it passes overhead.

but thanks for pointing out where the IF filter was. lol Im in a bit of a rush since if I miss this the next pass is 3 hours later.

Ok I'm spared.. next pass is in 59 Min.

 

[scannerrail]

Wow.. I'm totally shocked... now I really only got this radio for the NOAA sats but wow.. this radio beats my Radio Shack Pro 95 as far is receiving the signal...

When the Radio shack fades out it still comes in clear on the Jingtong.. I did a rough audio recording of it..

As soon as I can get the 2.5mm to 3.5mm audio adapter Im going to hook it up to my pc and trying to see if I can decode a picture..

I will have the audio files up in a little while


(morning coffee has me up!)

 

[scannerrail]

Ok here is the audio file.. kinda hard to juggle with me hanging out the window and having a short cable..

The radio Shack was hooked up via the discriminator tap and the Jingtong I had to place my mic over the speaker of the unit which is why you hear me moving around a bit so it wont take a 2 story drop on the grass below.

So first up is the radio shack Vs the jingtong both trying to get Noaa 18

http://rapidshare.com/files/38658432/RS_vs_JT.mp3.html


And here is the Jingtong alone by it's self after the test (radio Shack could no longer pick the signal up) And that was using the RS telescopic antenna extended all the way out.

by far the clearest i've ever heard it out sticking it out the window.

http://rapidshare.com/files/38658680/clear_JT.mp3.html

and included is me taking a picture while receiving the signal.. I don't think the signal bar really helps it seems to always default to 6 out of 8 bars...

I have it set to 5Khz steps default is 25Khz

 

[N4JNW]

Wow.. It lights up blue???? I want one now!!!! Oh.. Crap.. gotta watch spending...

 

[scannerrail]

lol everyone likes blue

hmm little things to watch out for is it seems like the charger will overcharge the batteries

and what the charger says it outputs (7.2V) is wrong.. as it's really 12.5V I took the radio off the charger after I took readings from the battery pack and it was reading 8.62V

 

[scannerrail]

stupid question but is it possible this has a discriminator output? or is that just a bit too much to expect?

trying to figure out how this Jingtong is more sensitive then my radio Shack pro 95