How to adjust VCO to get to 440 MHZ.

[N4KVE]

I've had a TK880-1 which is a 450-490 radio. I got it from a ham, & it works fine in the whole ham band that I use. 440-450. However, I'm told the VCO needs an adjustment to do this. Sure enough, I just got 2 similar radios right out of commercial service. They rx perfectly down to 443, but won't go any lower. Does anyone know how to adjust the VCO to go down a few more meg. I don't care about losing a few meg off the top. Thanks.

 

[MTS2000des]

check this thread Gary.

http://forums.radioreference.com/al...880-help-question-programming.html#post662251

 

[N4KVE]

Thanks Erik. I wouldn't touch anything unless I brought it to a radio tech with proper equipment. The previous owner of my first 880 which now does the whole ham band tried that mod with reckless abandonment. Really messed up the transmit. I brought it to a friend [radio tech] who fixed it right up. Funny though, while the new radio won't rx at 442, it transmits there just fine. I only see this guy twice a year, so I'll just wait until the next time. Thanks again.

 

[ramal121]

The VCO is easy. Put a voltmeter on TP-1. Select the highest frequency you have. Voltage should be 1.5V or greater. Go to the lowest frequency and TP-1 should be 8.0V or less. Adjust TX and RX VCOs separately so they fall within this range.

Don't fiddle with sensitivity or preselector coils unless you go by the manual.

 

[N4KVE]

I opened the radio, & at the low end the voltage is above 8.5, even on the 443, & 444 freq's where rx is fine. But at the risk of sounding stupid, what instrument do I adjust TC106, & TC109 with?

 

[ramal121]

Very small screwdriver. Non metallic is best. If you have a regular one wrap some tape around it. Shorting to the shield wrecks the reading.

Maybe easiest to program several frequencies 1 MHz apart and step the adjustment down bit by bit. There is a physical limit to where the VCO will lock but I'd be very surprised if you can't get it to 440MHz.

 

[cabletech]

I can see this as being a paper weight, door stop.

 

[N4KVE]

LOL, I'm not getting my fingers in the radio. All I did was check the VCO voltage. I have plenty of dual banders that rx from 400-500 should I need 442. But there's only 1 local machine on 442.050. The rest of the local machines work fine in the radio. The 880 is basically a GMRS radio, & it works great there. Plus a few simplex freq's I use.

 

[kayn1n32008]

I have plenty of dual banders that rx from 400-500 should I need 442.

Remember, you are trying to take a radio, designed for 450-490MHz (40MHz band width) and make it go 25%(10MHz) further than it was designed. Some brands of radios will only go a few MHz out of their rated band split.

Your 'dual banders' were designed to receive the whole range, even if it only transmits in the ham band.

Edit: I reread your statement and see you are explaining you have other option to get down to 442MHz.


Sent from my iPad using Tapatalk

 

[N4KVE]

I appreciate all the help.The radios were purchased by a friend to go on a County Cert system. Since the 880 I own was tuned to do the whole ham band, I thought it might be an easy "fix" to get his radios on the ham band too. But he also has plenty of dual banders that will do what he needs there. I'm not going to take a chance on his radios, but I will give him the info from this post, & he can do what he wants with it. While his ham radios have been modified to do the Cert freq's, he felt the $40 each the 880's cost [including 2 power supplies] was a cheap cost to stay legal, & also do true narrow band.