Modifying IF Bandwidth on a Radio

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hydrogenhead Power-User Join Date: Jan 2011 Location: Scotland Posts: 361	Modifying IF Bandwidth on a Radio 07/24/2012 8:56 AM
	I have a small handheld radio. It is a Baofeng UV 3R. It has a number of small copper coils inside it. How is the IF bandwith controlled or limited? Can it be extended by slightly tweaking the copper coils? I am needing at least 34 KHz of bandwitdth and my radio has a maximum of 25.
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Joshi Guru Join Date: Oct 2007 Location: India Posts: 1246 Good Answers: 34	#1 Re: Modifying IF Bandwidth on a Radio 07/24/2012 9:50 AM
	No. It is not possible to extend IF bandwidth by tweaking the core of the IF transformer. The IFT has to be loaded by a resistor PERHAPS. I am not very sure. I do not have the ARRL handbook at hand. Please checkup before trying.
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RAMConsult Guru Join Date: May 2007 Location: NYC metropolitan area. Posts: 3230 Good Answers: 444	#2 Re: Modifying IF Bandwidth on a Radio 07/24/2012 10:36 AM
	Google on baofeng uv 3r mods mods for more info on how to hack this SDR (Software Defined Radio). Those coils are probably on the transmitter side so anything you touch will probably screw-up the output signal. As an SDR you may be able to download software that will allow you to customize most of the parameters that define (get it) the way the radio behaves including such things as IF passband. But nothing is free in the world of RF even with modern DSP chips, increasing the passband probably comes at the expense of lower sensitivity, selectivity, and higher noise figure. Make sure you make a copy of the current firmware before you start changing things or you'll wind up with a handheld brick. This ain't your grandpa's Heathkit. __________________ “Tell me and I forget. Teach me and I remember. Involve me and I learn.” Ben Franklin.
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on7ami Active Contributor Join Date: Sep 2009 Location: Belgium - Zevergem Posts: 13	#3 Re: Modifying IF Bandwidth on a Radio 07/25/2012 4:13 AM
	If the IF section contains tree or more coils and you have a sweep generator and a scoop or a spectrum analyzer with tracking possibility then you can try to widen the bandwidth by detune two filters one a little up and one a little down. Another way is to lower the Q-factor of your IF Filters by adding a resistor in parallel over the filter. in both cases the senility of the if stage will lower too. If the IF part is working on a classical IF frequency 455Kc or 10.7 Mc you could consider replacing the LC-filters with a ceramic filter having the correct bandwidth. Remember that the detector has to be wide enough to handle the 34Kc too. Greets, __________________ All my knowledge comes from Allah (swt) praise Him not me...
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StandardsGuy Guru Join Date: Dec 2006 Location: North America, Earth Posts: 4528 Good Answers: 106	#4 Re: Modifying IF Bandwidth on a Radio 07/26/2012 12:37 AM
	Just tweak the center coil slug. It will increase, but maybe not enough. I have done this on AM radios. __________________ “I would rather have questions that can't be answered than answers that can't be questioned.” - Richard Feynman
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Joshi (1); on7ami (1); RAMConsult (1); StandardsGuy (1)

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