Cobra 142 gtl Alignment

[ExitThirteen]

It's about middle/back of the board towards the final. That is R101, which is connected to the base of TR13. That's your test point.

~Cheers~

 

[Robb]

Thank You Robb, so this method will work no problem with 95% shielded coaxial line?
The ground would be directly connected to the coax outter connector? I Have some magnet wire I can wrap 5 turns, tight like a tvi filter or like a spring?

When my scope comes in I will align this baby, for now I want to make sure it's on frequency, using this guide http://lesterscustoms.com/counter_to_uniden_single_conversion
With a different counter (8 digit fleabay special 2-wire hook up minus power)
I attached my counter to the point circled in the second picture, the frequency was not 10.240 Mhz (but jumping below and above) and was jumping without putting radio into tx.

I care to know i am on frequency so right now im wrapping a pick up coil.

Just connect both freq counter connections to each end of the coil wrapped around the coax. It works by induction. The coax itself has a magnetic field around it when transmit power is going thru the coax. That coil you added picks up a weak but measurable voltage thru that coil and is read by the frq counter. Anywhere from five to ten winds of wire around the coax is all that is necessary for the freq counter to read . . .

 

[LeapFrog]

Very well! Thank You ExitThirteen, & Mr. Robb!
I know on the 29 LTD it's R61 to hook up a 2 wire counter, i will be back with more.
Maybe tonight, maybe tomorrow.

 

[LeapFrog]

ExitThirteen I found it, awesome picture! I don't have any leaded solder at the moment and this is going to be a "permanent" install, I noticed while breezing through the alignment steps I may not be picking up the transmit frequency but a vco frequency that gets mixed with another, I haven't probed r101 with the counter yet but I take it I shouldn't need to build the RF sensing pick-up coil Robb mentions just to see the tx frequency, although I am going to do it for the
sake of knowledge. In fact im doing now, Ill post my results after. The counter will be powered from a nine volt battery to keep it "electrically seperated" (I know that's a misnomer) if it doesn't work I will tie in the two grounds together.

Sorry to hijack this thread gentlemen, it's just that it is a 142GTL and I am almost on-topic.

 

[LeapFrog]

Maybe I should reduce the amount turns, it worked!! Just bounced around a lot, and I know I have to re-align this radio soon. On 22 I did eventually see 27.223Mhz But it kept bouncing above and below by a lot.

I believe the wires leads should be kept short as possible and maybe even shielded wires running from the counter module to the pick up coil, can I attacth a ceramic to both ends of the coil in an effort to keep it more stable?

 

[Robb]

Turn the mic gain down to zero before you key the mic. This way, it should not 'bounce around' and give you a reading as accurate as your freq counter can provide.

BTW; what is the make and model of your freq counter?

 

[LeapFrog]

SANJIAN Studio PLJ-8LED-RS (search for PLJ-8LED or PLJ-6LED for the six digit model) Dirt Cheap from china, this is my first 4 months of Radio, and most of the money I spent on broken radios to learn on.
I have a decent DMM that reads true r.m.s. voltages, on my list are:
40-60Mhz Scope w/ RF probes
Signal generator

And modulation meter, good avg reading meter, and a p.e.p. meter.
Maybe I'll spring for a paradynamics "cheapy" that includes most of these meter in one.
Also going to buy / build a higher capacity dummy load

Edit: That is a good tip, do not modulate the carrier signal you are going to measure.
I have turned it all the way down and still had stability issues, going to shorten the leads.

 

[LeapFrog]

Bwaahh with the induiction coil it's now reading between 8-13Mhz??! After I took it down to six turns, and tied in the ground's 18-20Mhz, I take the inductor size, coax used, and other factors matter, so I am going to pull the covers off tomorrow and attatch it R101 to see what I get.

 

[LeapFrog]

I've got 7.7945 from r101 in AM. A horrible whine came through the speaker while the counter was powered up from a nine volt battery, I did not check usb, or lsb, nor did I try to power the counter from the radio.

instead i've pulled the wires back out and set this counter aside for now.