Cobra 148 MK2 10Khz off All Bands

A forum for the discussion of matters of a technical nature. All such activities are undertaken at the readers discretion and own risk. If you don't know what you are doing, don't blame us if it all goes wrong!
User avatar
cb4ever104
Veteran
Veteran
Posts: 4531
Joined: 28 Jul 2011, 21:26
Location: Alicante , España

Re: Cobra 148 MK2 10Khz off All Bands

Post by cb4ever104 » 25 May 2018, 13:04

Double post.
Last edited by cb4ever104 on 25 May 2018, 13:26, edited 1 time in total.
30TM060
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.

User avatar
cb4ever104
Veteran
Veteran
Posts: 4531
Joined: 28 Jul 2011, 21:26
Location: Alicante , España

Re: Cobra 148 MK2 10Khz off All Bands

Post by cb4ever104 » 25 May 2018, 13:06

currentstatus wrote:
25 May 2018, 13:00
Thanks Sammy!! I'll get some ordered now.. looks like I'm going to need a stock up in general :)
Hi m8 . No . Don't do that . As Tim mentioned . You can't measure the 10.695 signal on AM . You need to key up the radio and adjust the mixed 27Mhz signal . I forgot about that . The correct procedure is in the manual . The manual says that you can do it on CW , but I've never tried it . Saying that your USB and LSB offsets need adjusting regardless.

For me you need to go through the complete carrier alignment stage in the service manual .

Sammy
30TM060
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.

currentstatus
Regular
Regular
Posts: 45
Joined: 18 May 2018, 06:50
Location: Valencia, Spain

Re: Cobra 148 MK2 10Khz off All Bands

Post by currentstatus » 25 May 2018, 13:09

cb4ever104 wrote:
25 May 2018, 13:06
currentstatus wrote:
25 May 2018, 13:00
Thanks Sammy!! I'll get some ordered now.. looks like I'm going to need a stock up in general :)
Hi m8 . No . Don't do that . As Tim mentioned . You can't measure the 10.695 signal on AM . You need to key up the radio and adjust the mixed 27Mhz signal . I forgot about that . The correct procedure is in the manual . The manual says that you can do it on CW , but I've never tried it . Saying that your USB and LSB offsets need adjusting regardless.

For me you need to go through the complete carrier alignment stage in the service manual .

Sammy
OK will do.. thanks.

currentstatus
Regular
Regular
Posts: 45
Joined: 18 May 2018, 06:50
Location: Valencia, Spain

Re: Cobra 148 MK2 10Khz off All Bands

Post by currentstatus » 25 May 2018, 13:09

Guys.. thanks for helping out!
As you can tell I'm fairly new to radio repair "but I'm learning fast".. I've been doing audio gear for a few years.

Seem to be catching the bug with these Unidens tho.. enjoying this :)

User avatar
Otter
Veteran
Veteran
Posts: 2715
Joined: 04 Apr 2008, 21:42
Call Sign: 26TM439

Re: Cobra 148 MK2 10Khz off All Bands

Post by Otter » 25 May 2018, 18:42

The binary adders look to be OK. Are you sure that you're receiving on the same frequency that you're transmitting on?
"To this day the words Stirling bridge conjour pride in every Scotsman's heart, while to an Englishman those same words conjour literally no feelings at all." - Cunk on Britain S1 E1
Gorgon Brown - a man with all the joie de vivre of a haunted cave in Poland. S1 E3

currentstatus
Regular
Regular
Posts: 45
Joined: 18 May 2018, 06:50
Location: Valencia, Spain

Re: Cobra 148 MK2 10Khz off All Bands

Post by currentstatus » 25 May 2018, 19:14

Otter wrote:
25 May 2018, 18:42
The binary adders look to be OK. Are you sure that you're receiving on the same frequency that you're transmitting on?
Yes Tim.. all through the bands same TX and RX freq on the sig gen.

Is there any component anywhere which would add or adjust for the additional 10Khz ??

User avatar
Otter
Veteran
Veteran
Posts: 2715
Joined: 04 Apr 2008, 21:42
Call Sign: 26TM439

Re: Cobra 148 MK2 10Khz off All Bands

Post by Otter » 25 May 2018, 20:32

10.6925 MHz for USB on TP6 is correct, as is 10.6975 MHz for LSB
"To this day the words Stirling bridge conjour pride in every Scotsman's heart, while to an Englishman those same words conjour literally no feelings at all." - Cunk on Britain S1 E1
Gorgon Brown - a man with all the joie de vivre of a haunted cave in Poland. S1 E3

User avatar
Otter
Veteran
Veteran
Posts: 2715
Joined: 04 Apr 2008, 21:42
Call Sign: 26TM439

Re: Cobra 148 MK2 10Khz off All Bands

Post by Otter » 25 May 2018, 20:45

So what's the frequency in FM Rx mid block CH. 19 on L21 when the voltage on L18 is 4V or so? Now what's the same frequency in Tx? Is the frequency stable?
"To this day the words Stirling bridge conjour pride in every Scotsman's heart, while to an Englishman those same words conjour literally no feelings at all." - Cunk on Britain S1 E1
Gorgon Brown - a man with all the joie de vivre of a haunted cave in Poland. S1 E3

currentstatus
Regular
Regular
Posts: 45
Joined: 18 May 2018, 06:50
Location: Valencia, Spain

Re: Cobra 148 MK2 10Khz off All Bands

Post by currentstatus » 26 May 2018, 10:39

Otter wrote:
25 May 2018, 20:45
So what's the frequency in FM Rx mid block CH. 19 on L21 when the voltage on L18 is 4V or so? Now what's the same frequency in Tx? Is the frequency stable?
ch19 Mid AM/FM = 16.5000 MHz is locked when adjusting L18 (TP-2) at between 1.3v - 7.6v
ch19 Mid USB = 16.5016 MHz is closest I can get it to 16.5025 (considering we're 10KHz above)
ch19 Mid LSB = unstable, hovering around 16.489

So if I go down to ch18.. I can pretty much lock AM/FM/USB correctly. LSB there is an issue there but I think this 10Kc issue is 1st.
Saying that.. is the LSB issue related?

currentstatus
Regular
Regular
Posts: 45
Joined: 18 May 2018, 06:50
Location: Valencia, Spain

Re: Cobra 148 MK2 10Khz off All Bands

Post by currentstatus » 26 May 2018, 10:46

Actually no I can't lock USB on ch18.. best is 16.4916 with slug at bottom. AM is fine 16.4900 and TX is clean.

User avatar
cb4ever104
Veteran
Veteran
Posts: 4531
Joined: 28 Jul 2011, 21:26
Location: Alicante , España

Re: Cobra 148 MK2 10Khz off All Bands

Post by cb4ever104 » 26 May 2018, 11:29

Otter wrote:
25 May 2018, 20:32
10.6925 MHz for USB on TP6 is correct, as is 10.6975 MHz for LSB
Yeah . I was reading it back to front . Next time I should have the manual in front of me before opening my big trap .... :silent: :silent: :silent:
30TM060
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.

sonoma
Regular
Regular
Posts: 76
Joined: 29 Oct 2017, 04:12

Re: Cobra 148 MK2 10Khz off All Bands

Post by sonoma » 26 May 2018, 20:07

I* have never seen the manual for this radio. are you sure they did not make an error in the manual. most radios I have ever worked on the usb is
is the higher version 10.6975 and LSB is 10.6925. I have seen the sams book misprint on a few radios a few times.just a question since I have never seen this radio. USB is normally the higher reading. take a look at this.

User avatar
cb4ever104
Veteran
Veteran
Posts: 4531
Joined: 28 Jul 2011, 21:26
Location: Alicante , España

Re: Cobra 148 MK2 10Khz off All Bands

Post by cb4ever104 » 26 May 2018, 21:26

Haha. I thought it looked wrong the first time I saw it. Then I looked at the manual and thought I'd made a mistake, but it's been bugging me all afternoon 😀
30TM060
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.

sonoma
Regular
Regular
Posts: 76
Joined: 29 Oct 2017, 04:12

Re: Cobra 148 MK2 10Khz off All Bands

Post by sonoma » 27 May 2018, 00:08

let us know if that was the problem.

User avatar
cb4ever104
Veteran
Veteran
Posts: 4531
Joined: 28 Jul 2011, 21:26
Location: Alicante , España

Re: Cobra 148 MK2 10Khz off All Bands

Post by cb4ever104 » 27 May 2018, 08:22

sonoma wrote:
27 May 2018, 00:08
let us know if that was the problem.
It's not me who's got the problem.

Also , I think the manual is right . I've been tuning it over the years without really giving it much thought , but I think you're actually adjusting the frequency of the sideband that gets removed by the filter . I'll need to go back and look at that section again .
30TM060
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.

Post Reply

Who is online

Users browsing this forum: No registered users and 8 guests