Cobra 29GTL/LTD ?

[Techno1]

On the Cobra 29 ltd/gtl and the Dwight D and cobra 1000.

Is there a location on the pc board to monitor the frequency with a freq counter.

I know on the Cobra 142/Madisons/Washington and radios that use the MB8719/8735 pll TP 1 which is a resistor on 1 side is a good place to monitor the frequency. Is there a point on the AM radios mentioned above to do this?

thanks

 

[nomadradio]

There is, but you'll have to choose whether you want to display the receive or the transmit frequency. The radio's PLL jumps down 455 kHz when you key the mike. The fleabay PLJ6-LED counter board has an offset feature you can set for most any radio, but the AM radios you mention all share this " transmit jump" design.

On a Cobra 29LTD I would use the output side of L18. One side has two pins, the other side has three. One end of the 3-pin side is ground, you want the opposite "hot" side of L18. Use a 100 ohm or higher resistor between L18 and the counter input. Most counters have a blocking capacitor on their input, so a resistor alone should serve to keep the counter input from loading down the radio's PLL source. That would reduce receiver sensitivity and transmit power.

In a Cobra 1000 or 89GTL it's labeled "TP2", on the output of L18.

Sure wish somebody sold a version of the PLJ6 with multiple offsets selectable by input ports like the Galaxy built-in frequency displays. Would solve the problem for these AM-only radios.

73

 

[Techno1]

I have 2 of these on the way and was hoping to install 1 in a cobra 29ltd that has 80 extra channels.
So it will read receive and what will happen on transmit nothing will show?

Here is the pdf for the OLED and I dont see any offset function

thanks

https://www.aliexpress.us/item/3256811601643160.html?spm=a2g0o.productlist.main.1.f93be0b1rhcUUQ&algo_pvid=665a03d0-69f2-4260-b12e-60228662b071&algo_exp_id=665a03d0-69f2-4260-b12e-60228662b071-0&pdp_ext_f=%7B%22order%22%3A%224%22%2C%22spu_best_type%22%3A%22price%22%2C%22eval%22%3A%221%22%2C%22fromPage%22%3A%22search%22%7D&pdp_npi=6%40dis%21USD%2137.82%2114.47%21%21%21259.04%2199.10%21%402101dedf17735818568303929e3d21%2112000056552733616%21sea%21US%21130083706%21X%211%210%21n_tag%3A-29919%3Bd%3Ab03e6a71%3Bm03_new_user%3A-29895%3BpisId%3A5000000201534772&curPageLogUid=tSRUsBh6nNjC&utparam-url=scene%3Asearch%7Cquery_from%3A%7Cx_object_id%3A1005011787957912%7C_p_origin_prod%3A

 

[Techno1]

if L18 is for receive what point will be for transmit.

What about a small relay that the input to the relay common is the counter.
And 1 receive point goes to 1 pole and the transmit the other pole.
so when u key it will show Transmit and no key it will show receive.

You can use pin 3 as the key for the relay.
I have these real small mini relays that would work perfect if it will work.

i guess i will have to try when the OLED counters arrive.

Someone mounted 1 in this SSB radio

 

[Techno1]

So I was probing around a Cobra 29LTD and I see L18 is transmit no receive and I did not find a location to monitor receive so I guess adding 1 of these to a Cobra 29/25 and other AM radios is not a good thing at the moment as you will only be able to get transmit to activate the OLED counter.

 

[nomadradio]

Pretty sure the local-oscillator signal is still present at that test point for receive and transmit.

The ALI Express OLED counter says it has two offsets. Might be able to jigger it to read properly for transmit and receive. The ad listing didn't explain how to select one offset or the other.

73

 

[Techno1]

Pretty sure the local-oscillator signal is still present at that test point for receive and transmit.

The ALI Express OLED counter says it has two offsets. Might be able to jigger it to read properly for transmit and receive. The ad listing didn't explain how to select one offset or the other.

73

What is the test point location for the 29 ltd/gtl?

 

[Techno1]

Nomadradio.
Is there a section in the 29s that the receive can be monitored I tried and could not find any.

thanks

 

[TM007]

"Here is the pdf for the OLED and I dont see any offset function"

Run the manual through translation and you'll get the following.

IF Offset Setting​

The configuration or switching between the two intermediate frequencies (IFs) is controlled by the logic level on pin 3 of the ICSP programming interface.

• When pin 3 is set to a high level or left floating, the first IF is selected and used.
• When pin 3 is set to a low level, the second IF is selected and used.

The two IFs are independent of each other. Their IF values and add/subtract modes can be preset separately without mutual interference.

• With pin 3 high or floating, the first IF is configured.
• With pin 3 low, the second IF is configured.

At the factory, pin 3 is left floating by default, which selects the first IF. The default IF value is zero, and the add mode is selected.

In practical applications, pin 3 and pin 4 (or pin 2) of the ICSP interface are brought out using a 2‑pin Dupont cable (location indicated by the red circle in the figure below). A switch or microcontroller can then be used to control the logic level of ICSP pin 3, enabling synchronized switching between the two IFs and the transceiver.

 

[nomadradio]

Holy moly! That should work. A diode with the anode on pin 3 of the display. The cathode would go to pin 3 of the mike jack. This would select the second offset value in transmit, and the first one for receive.

Cool!

73

 

[TM007]

I thought the same was true of the PLJ 6LED or PLJ 8LED? early ones had the 6pin DuPont connecter (Program Interface), still there on the more recent ones, just without the pins.

Probably for a different thread, but here goes. So a PLJ6 or 8 or this OLED version would require 3 offsets to handle an SSB radio?

A: The Radios IF Frequency.
B: Upper Sideband offset.
C: Lower Sideband offset.

Probably depends on the radio but i was thinking along the lines of older uniden 858's etc.

 

[Cable Guy]

So a PLJ6 or 8 or this OLED version would require 3 offsets to handle an SSB radio?

A: The Radios IF Frequency.
B: Upper Sideband offset.
C: Lower Sideband offset.

Correct, I just put one in an 8719 Madison, and it's 1 offset shy of all three, so AM and LSB show correctly, but USB does not. I used a spdt relay fed from the mode switch to select the correct IF, but Nomad's diode junction could work well and be cheaper than a relay.

 

[Techno1]

Correct, I just put one in an 8719 Madison, and it's 1 offset shy of all three, so AM and LSB show correctly, but USB does not. I used a spdt relay fed from the mode switch to select the correct IF, but Nomad's diode junction could work well and be cheaper than a relay.

Did you use TP 1 for the madison?

 

[Cable Guy]

Did you use TP 1 for the madison?

Yes, but you need a resistor, 100 1000 100 ohm AND capacitor, 10pf. Skip the capacitor and you get counter noise back feed. Skip the resistor and the counter loads down TP1. Good luck!

Edited to verify resistor value.

 

[Techno1]

I have 2 of these on the way this week and was hoping to put in a cobra 29ltd/gtl Am radio with 80 extra channels. I found a transmit location to monitor transmit but cant find a location for the AM receive I know about the 455Khz down shift in transmit. If there is a spot could someone chime in for receive.

thanks