PC-244: My first PLL removal and replacement

[dt307]

It's not the module or the rig
When a 40ch radio is made and setup it's just that it's set to work at its best over the 40 ch range .
As you expand the range of the radio. Normally you will find the rx and tx will drop out on one end or on both ends of the extra channels.most will require the rx and tx to be broadbanded to cover the extra frequencies. Or it will be deaf and little tx power.
Most a simple tweak will get you what you need.
Or get you a workable solution.
To get the same power output and the same rx on all frequencies of a 40ch radio been mod by module.pic.eprom.diode.matrix.ect can require some extra work than a tweak .

Hope that explained it or I will get my coat

[lbcomms]

you will find the rx and tx will drop out on one end or on both ends of the extra channels.most will require the rx and tx to be broadbanded to cover the extra frequencies. Or it will be deaf and little tx power

The cause of the dropoff is the mixers, they are fairly narrow in that chassis.

There are two ways around it, make them wider or make them tunable. Wider is easier / cheaper at design time, but is noisier / more susceptible to interference than a tuneable setup. Commercial receivers only use tunable mixers where extreme ranges are required, such as VHF/UHF scanners.

For a modification project, a few varactors and passives can make the mixers tunable. This will give up to 3MHz of coverage with minimal dropoff. We did one about a year ago, details here:

viewtopic.php?f=53&t=49419#p437916

A DC voltage rising with frequency is needed to tune the varactors on the mixers. This can be sourced from the PLL tuning voltage in most cases, and the inductive part (the tuning slugs) aligned so the peak on the mixers tracks the frequency the radio is set to.

[dt307]

ive seen your work Sue and its second to none.
when i did some work on one of the same type chassis it was a bit tight but it was within what i wanted from it and i have no one else to please but my self,i was not a fan of that chassis but i liked the small form factor of it

i would love in the future to make my own add on boards avr on board pll ect but not been able to find the time to look into where to even start
be nice to add a rotary encoder into the mix as well

i understand about the varactor bit and that is indeed a neat party trick i may use at some point if needed.

thanks for the input Sue

[harakiri]

you will find the rx and tx will drop out on one end or on both ends of the extra channels.most will require the rx and tx to be broadbanded to cover the extra frequencies. Or it will be deaf and little tx power

The cause of the dropoff is the mixers, they are fairly narrow in that chassis.

There are two ways around it, make them wider or make them tunable. Wider is easier / cheaper at design time, but is noisier / more susceptible to interference than a tuneable setup. Commercial receivers only use tunable mixers where extreme ranges are required, such as VHF/UHF scanners.

For a modification project, a few varactors and passives can make the mixers tunable. This will give up to 3MHz of coverage with minimal dropoff. We did one about a year ago, details here:

viewtopic.php?f=53&t=49419#p437916

A DC voltage rising with frequency is needed to tune the varactors on the mixers. This can be sourced from the PLL tuning voltage in most cases, and the inductive part (the tuning slugs) aligned so the peak on the mixers tracks the frequency the radio is set to.

Nice info as always Sue.
It still is probably a little above my level of understanding,but one time has to be the first,so I guess this would be the radio I`ll use as my learning kit. Hopefully I could find the parts needed. I got a Uniden VHF/UHF handheld scanner somewhere in a box for parts..Not that I know it got what I need,but who knows..

So much to learn.

[lbcomms]

The scanner uses the same principle but the frequency range is so far removed that different spec parts would be used in that application (they would have a much lower total capacitance so they would be usable into the hundreds of MHz). Also, they would likely be tiny surface mount devices, so you'll need to have a hot air rework station and the associated tools to play with.

In your application, use conventional through hole components, and ones suitable for the frequency range. BB809 varactors will give you 2MHz coverage with minimal dropoff, are big enough to handle with a regular soldering iron, and can be had from eBay in small quantities:

http://www.ebay.co.uk/itm/BB809-VARICAP ... SwU-pXrFMs

They can be had cheaper from China, but are likely to be fakes. Buyer beware

The other parts can be found in a junker radio or bought locally - 0.01uF (10nF) ceramic capacitors and 100K carbon or metal film resistors.

Edit: you will need 3 or 4 of each of the above to do one radio

If you want to have a go, get the parts and I'll post a drawing showing how to connect it all up...

[harakiri]

The scanner uses the same principle but the frequency range is so far removed that different spec parts would be used in that application (they would have a much lower total capacitance so they would be usable into the hundreds of MHz). Also, they would likely be tiny surface mount devices, so you'll need to have a hot air rework station and the associated tools to play with.

In your application, use conventional through hole components, and ones suitable for the frequency range. BB809 varactors will give you 2MHz coverage with minimal dropoff, are big enough to handle with a regular soldering iron, and can be had from eBay in small quantities:

http://www.ebay.co.uk/itm/BB809-VARICAP ... SwU-pXrFMs

They can be had cheaper from China, but are likely to be fakes. Buyer beware

The other parts can be found in a junker radio or bought locally - 0.01uF (10nF) ceramic capacitors and 100K carbon or metal film resistors.

Edit: you will need 3 or 4 of each of the above to do one radio

If you want to have a go, get the parts and I'll post a drawing showing how to connect it all up...

Thanks so much Sue.
I will order those. 2 Mhz coverage sounds great. It would be even more than I hoped for,and more than enough for this project. It was in UK,so it should not take much time. The Ceramics and film resistors I`d also have to order,and would look for a safe seller for those as well. "This byer is aware" .. Or at least getting there.

Cheers.

[harakiri]

Then I`ve ordered ceramics (from china,but looks like a good seller,so we`ll give it a try.) Also ordered 2x3 of the varicap diodes. I had resistors. The parts is already shipped,so hopefully it would not take long. This is gonna be very interesting. (Almost getting a butterfly feeling here. That lucky radio is getting it all.. )

I was reading a bit to quick here the first time reading the last posts. I actually thought the parts had to be found here and there. (ie. scanners) I need to make myself a quite reading corner to up my concentration. So much going on here in daytime. Reading again (still a few more times to go,hehe) I understand more, thanks to Chris and Sue. (And a general thanks to the forum is also well deserved.)

dt307, I also kinda like the small size of the chassis. And actually, the Uniden pc-244 is not a bad looking radio. But I don`t mind "bling" ... hehe

[lbcomms]

The ceramics will likely take a while to arrive, so that should tie in OK, we'll be busy for the next week or so finishing up for the Christmas break.

From next week until about mid January we'll have a lot more time to play. I'll try to do the drawing in the next day or two to get you started...

[harakiri]

Yes,I can`t say I expect anything to arrive quickly in these xmas times,as mail here tends to go extremely slow in this month. In this case though,I`m not in a hurry. Xmas planing is anyway taking up lot of time this week and start of next.

I am looking forward to getting over the xmas planing. It should free up a lot of time.

Cheers.

[harakiri]

Happy new year everyone.
Hope everyone is doing great.

So that was quite the xmas and new-years eve here.. Lightning gave the island I live on black out several times,and brought the cell-phone down for a month or so..(at least that gave me radio-time).. It also wrecked a server,router and some long distance broad-band antennas.
I went from happy nerding with radios,to becoming the computer-nerd in no time. It piled on for months and I am now finally getting things back to normal.

I thought I better update this tread first as I actually got the parts right after xmas if I`m not mistaken,but my radio-room was turned in to a computer-area (I prefer radios though) for the first 2-3 months of the year. I actually had to put my soldering station in a box to make place for computer related things.. Believe me,its not fun.. The only thing making it mildly ok. was that it was not Microsoft-related problems. I am way better when it comes to Linux/unix-systems than windows..

However the other day I finally could get back to the radio`s. And that is truly a blessing.

So much catching up to do.. I need to read through the forum this coming weekend so I can catch up with you all,and your on-going projects.

Cheers friends.

[cb4ever104]

Good to see you back H !

S.

[harakiri]

Good to see you back H !

S.

Ah,thank you S. It is great to see you too. I hope life is treating you nice down there in Spain.

-H