TK-690 6 meter conversion - Low RF out

[kb6nzv]

Hello Everyone,

I am working to understand one result of a successful TK-690 conversion to the 6 meter band.
Big issue is lower than expected RF output levels. VCO voltages seem to me to be correct. Following my mod, the TX and RX VCO's do not go out of lock now anywhere between 42 to 54 Mhz. These results are consistent on two modified 690's.

I have looked closely at the service manual and verified that in the radio's firmware settings that the output level is set correctly. I have tested the radio into a dummy load with an inline power meter and in a vehicle with the same results - low output. Is it possible the low output is proportional to VCO voltage?

I did not use a 1/8 inch brass slug as I didn't have that handy. Instead, I used 1/8 inch (14 AWG) 14-MAG PE wire instead. It seems to have worked perfectly aside from the lower than expected output level. Am I using the wrong material?

Has anyone found they needed to tweak the output coils as you would with GE Rangr's moved to 6 meters?
If that's the next step, would anyone who did that be kind enough to post photos?

Vy73,
Phil KB6NZV

 

[prcguy]

Generally speaking, VCO output a little out of range should be similar to normal operation and I would suspect PA tuning or low pass filtering causing the low output.

You can make up a wooden or plastic stick with a ferrite slug on one end and brass on the other and use that to determine the need for further tuning. Place the ferrite then brass end near a coil and usually one will increase signal in a circuit and the other will decrease signal. If I remember right if the ferrite increases signal or power you would spread a coil apart and if brass increases power squeeze the coil together. Or maybe it was the opposite, its been awhile.
prcguy

 

[kb6nzv]

Generally speaking, VCO output a little out of range should be similar to normal operation and I would suspect PA tuning or low pass filtering causing the low output.

You can make up a wooden or plastic stick with a ferrite slug on one end and brass on the other and use that to determine the need for further tuning. Place the ferrite then brass end near a coil and usually one will increase signal in a circuit and the other will decrease signal. If I remember right if the ferrite increases signal or power you would spread a coil apart and if brass increases power squeeze the coil together. Or maybe it was the opposite, its been awhile.
prcguy

Many Thanks for the feedback!

Because I was certain there could be unexpected results, the slugs I made are held in the coil with bees wax and easily removed. That'll make trying your suggestions pretty easy to try out. Since the core of the two VCO coils is large enough, I'd also considered a doubled-over piece of the same MAG wire and test the result.

I have plenty of radios to harvest slug cores from to try your suggestion, but all the ones I've found would require either sanding or grinding off the threads so it could easily slip into the two VCO coils for testing. Voltages I measured ranged from just under 2 VDC to just over 5 VDC which made sense.
I recall the retuning trick you describe, but its been a long time since I tried modding a radio so I'm being somewhat cautious so I don't let and of the magic smoke escape.

My trick for carefully spreading coils (if it comes to that) is to use an old plastic card I cut as narrow with one edge sanded to an edge and then slip between each coil turn so the end result is uniform spreading that's easily reproduced or reversed.

 

[prcguy]

My suggestion of slugs on a stick is not to screw into a coil form but rather hold it close to a coil to see if more or less inductance is needed. If the circuit is happier with ferrite close by then it needs more inductance. If brass close by is better then it wants less inductance.
prcguy

Many Thanks for the feedback!

Because I was certain there could be unexpected results, the slugs I made are held in the coil with bees wax and easily removed. That'll make trying your suggestions pretty easy to try out. Since the core of the two VCO coils is large enough, I'd also considered a doubled-over piece of the same MAG wire and test the result.

I have plenty of radios to harvest slug cores from to try your suggestion, but all the ones I've found would require either sanding or grinding off the threads so it could easily slip into the two VCO coils for testing. Voltages I measured ranged from just under 2 VDC to just over 5 VDC which made sense.
I recall the retuning trick you describe, but its been a long time since I tried modding a radio so I'm being somewhat cautious so I don't let and of the magic smoke escape.

My trick for carefully spreading coils (if it comes to that) is to use an old plastic card I cut as narrow with one edge sanded to an edge and then slip between each coil turn so the end result is uniform spreading that's easily reproduced or reversed.

 

[kb6nzv]

My suggestion of slugs on a stick is not to screw into a coil form but rather hold it close to a coil to see if more or less inductance is needed. If the circuit is happier with ferrite close by then it needs more inductance. If brass close by is better then it wants less inductance.
prcguy

Gotcha!

 

[kb6nzv]

My suggestion of slugs on a stick is not to screw into a coil form but rather hold it close to a coil to see if more or less inductance is needed. If the circuit is happier with ferrite close by then it needs more inductance. If brass close by is better then it wants less inductance.
prcguy

Hey Prcguy:

Just a quick note as I'll finally have time this weekend to try your idea. Life keeps getting in the way so this is taking longer than anticipated. FWIW, I did install a lowband Antenex NMO antenna on the vehicle for testing and I'm getting between 6 to 10 watts out. It'll be interesting to see if the power level tracks with VCO drive levels.

If your suggestion doesn't give me the higher power level I'll start focusing on the coils for the drivers on the PA deck and see what she'll do.

Anybody else who's done this mod is welcome to share their results.

 

[mrweather]

I did the mod on my 690 using brass slugs and didn't notice any drop in RF out. I did manually turn it down to about 80 watts as suggested by someone else due to hams' habits of being longwinded.

 

[kb6nzv]

Update

As it turns out, using brass rod stock made all the difference. The radio has about 80 watts out and stays in lock through the entire frequency range. WooHoo!

 

[mm]

Now all you need is some e to get 6 FM moving.

Is there a 6 meter repeater near Lincoln City or are you going to try some of the 6 meter repeaters around Salem or Portland.

Mike in Salem

using Ge Rangr, GE orion, Motorola Maxtracs on both 6 and 10FM

I think i'm addicted to 6n10 meters

 

[kb6nzv]

I did the mod on my 690 using brass slugs and didn't notice any drop in RF out. I did manually turn it down to about 80 watts as suggested by someone else due to hams' habits of being longwinded.

At the time I had no brass rod stock to work with, so i tired using Mag wire instead; which mostly worked. )

 

[kb6nzv]

Now all you need is some e to get 6 FM moving.

Is there a 6 meter repeater near Lincoln City or are you going to try some of the 6 meter repeaters around Salem or Portland.

Mike in Salem

using Ge Rangr, GE orion, Motorola Maxtracs on both 6 and 10FM

I think i'm addicted to 6n10 meters

LoL! The closest repeater would be on Mt. Hebo and I'm able to hit that from the driveway.
All my prior work on Six has been SSB, so FM will be interesting to try with chances for Sporadic skip.
I suppose that'll sound a bit like Polar flutter, depending on the sort of reflection I'm working.

I'll see how many machines I can hit from work, closest will be Newberg. Do you know if any repeaters might be cross-band linked?

 

[Project25_MASTR]

I did the mod on my 690 using brass slugs and didn't notice any drop in RF out. I did manually turn it down to about 80 watts as suggested by someone else due to hams' habits of being longwinded.

Did the conversion on a bunch of TxDOT surplus radios…one was outputting 150W before we realigned the PA back to 100W.

 

[mm]

52.99/51.29 100hz ctcss, silver falls state park at >2000 feet elevation linked at times to 145.29
53.13/51.43 107.2 hz ctcss, portland area very wide coverage at ~3700 feet elevation, but not linked
52.83/51.13 107.2 hz ctcss linked to 145.27 some kind of RACES or ARES nets
52.85/51.15 107.2 hz ctcss may also be linked to 29.68 portland area rptr

Your best repeater would be the 53.13 repeater above, then the 52.83 and 52.85 repeaters, maybe even 52.99 from newberg.

I use 53.13 regularly with a motorola mt1000 ht and rubber duck from Salem at 58 miles distance and also of course my base using 3 el beam and various 110watt mobiles.

I have a 220MHZ remote base that has 6 and 10meter motorola maxtrac's cross linked to it so I can pick any of the above repeaters.

HEBO, 53.11, I believe is tough from my Salem qth mainly cuz my 6 meter antenna on the remote is a 5 element horizontal 6n10 dualbander and Hebo is partially shadowed but 53.13 and 52.99 are easy even with the horizontal antenna.

 

[kb6nzv]

52.99/51.29 100hz ctcss, silver falls state park at >2000 feet elevation linked at times to 145.29
53.13/51.43 107.2 hz ctcss, portland area very wide coverage at ~3700 feet elevation, but not linked
52.83/51.13 107.2 hz ctcss linked to 145.27 some kind of RACES or ARES nets
52.85/51.15 107.2 hz ctcss may also be linked to 29.68 portland area rptr

Your best repeater would be the 53.13 repeater above, then the 52.83 and 52.85 repeaters, maybe even 52.99 from newberg.

I use 53.13 regularly with a motorola mt1000 ht and rubber duck from Salem at 58 miles distance and also of course my base using 3 el beam and various 110watt mobiles.

I have a 220MHZ remote base that has 6 and 10meter motorola maxtrac's cross linked to it so I can pick any of the above repeaters.

HEBO, 53.11, I believe is tough from my Salem qth mainly cuz my 6 meter antenna on the remote is a 5 element horizontal 6n10 dualbander and Hebo is partially shadowed but 53.13 and 52.99 are easy even with the horizontal antenna.

Thanks for those details! I'll be sure to add those when the XYL is busy with her gardening. )
Once I have those loaded in the radio, I'll test both at home and work - should be interesting!

 

[kb6nzv]

52.99/51.29 100hz ctcss, silver falls state park at >2000 feet elevation linked at times to 145.29
53.13/51.43 107.2 hz ctcss, portland area very wide coverage at ~3700 feet elevation, but not linked
52.83/51.13 107.2 hz ctcss linked to 145.27 some kind of RACES or ARES nets
52.85/51.15 107.2 hz ctcss may also be linked to 29.68 portland area rptr

Your best repeater would be the 53.13 repeater above, then the 52.83 and 52.85 repeaters, maybe even 52.99 from newberg.

I use 53.13 regularly with a motorola mt1000 ht and rubber duck from Salem at 58 miles distance and also of course my base using 3 el beam and various 110watt mobiles.

I have a 220MHZ remote base that has 6 and 10meter motorola maxtrac's cross linked to it so I can pick any of the above repeaters.

HEBO, 53.11, I believe is tough from my Salem qth mainly cuz my 6 meter antenna on the remote is a 5 element horizontal 6n10 dualbander and Hebo is partially shadowed but 53.13 and 52.99 are easy even with the horizontal antenna.

I'll finally get a chance to add those tomorrow night after work.
I did finally intercept activity on the HEBO machine, seems more like someone's private rather than an open machine. Doesn't seem to be linked to anything either. My initial testing will be from Turner and Willamina.