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TK-690 Intermittent Receive Issue

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Captain715

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107
Location
Columbia, PA
I have a TK-690 mobile installed in a fire truck, that is having some sporadic receive issues. I will give a brief system setup, then explain what is happening.

The following communications equipment is installed in a 2009 Crimson Custom Pumper:

1) TK-690 (programmed in the 33MHz range, primary TX/RX of 33.64)
2) Pyramid SVR-250U (operating 450 - 470MHz)
3) Midland STX (Operating 150.995MHz)
4) WiFi/GPS/Cellular antenna for WiFi Hotspot and GPS receive for Mobile MappingSoftware
5) Panasonic Toughbook laptop in a mobile dock

Antennas are all located on the front of a 22" raised roof cab, giving as much separation as physically possible, locations are as follows (I will attach photo of the roof as soon as I get one):
1) VHF-Lo on driver side rear
2) UHF on driver side front
3) VHF on passenger rear
4) WiFi/GPS/Cellular is on passenger front

Antennas are staggered front to back, front being toward the center and rear to the outside,taking into account the roof mounted air conditioning unit in the center of the roof and the lightbar mounted on the front edge of the roof.

The issue that is occurring is sporadic and so far I can not reproduce it. When the Kenwood is set to receive on 33.64, it has been receiving 33.72 clearly. This has occurred about 4 times in the past 6 months or so. I had the radio tech out 3 times for this issue so far, and we have nothing out of spec. We currently have the squelch open just slightly below being deaf (.32uV I believe), and the front end is as tight as it will go. deviation is very low (below Kenwood factory spec's). We have even gone as far as to feed 33.72 directly into the radio using a service monitor, and still were not able to reproduce the problem. I am sure the signal is being received through the Kenwood, as each time this has occurred, the Pyramid repeater has been powered off.

Any suggestions as to where to look next, or what to try, I am open for ideas.
 

SCPD

QRT
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Not sure if this will help but.... I have a TK-790H in my POV with a similar problem. Recently, the receive sensitivity went bad. It would receive but the incoming signals sounded weak. I took it to our local Kenwood dealer/repair facility and they had to send it to Kenwood depot. The depot replaced some SMT components (unkown which ones), re-aligned it, and now it seems to receive better than before it went bad. Not sure if you've went this route yet but it may be a consideration.
 

AA4TX

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IONAFLXARS0
Have the ceramic IF filter checked. I have seen a rash of the TOKO filters going bad lately
 

Captain715

Member
Joined
Mar 4, 2004
Messages
107
Location
Columbia, PA
Not sure if this will help but.... I have a TK-790H in my POV with a similar problem. Recently, the receive sensitivity went bad. It would receive but the incoming signals sounded weak. I took it to our local Kenwood dealer/repair facility and they had to send it to Kenwood depot. The depot replaced some SMT components (unkown which ones), re-aligned it, and now it seems to receive better than before it went bad. Not sure if you've went this route yet but it may be a consideration.

The receive sensitivity is good, signals received are clear and strong, even the off frequency reception that is occurring. As stated above, everything meets or exceeds Kenwood factory spec's.

Have the ceramic IF filter checked. I have seen a rash of the TOKO filters going bad lately

We have not opened the radio at this point, everything has been done with a service monitor and the software interface. How would I go about checking the IF Filters if we wanted to go this route?

Thanks for the replies so far, keep them coming...
 
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Av8tor56

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72
Location
Roswell, NM
Just out of curiosity: where exactly is the truck when you've had the RX issues? Also, what's the power output and reflected power?
 

AA4TX

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We have not opened the radio at this point said:
That’s the tough one in an intermittent failure situation. You would see loss of sensitivity. On other bands VHF hi and UHF, it is easy: program the same frequency into two channels, one narrowband and one wideband. When the situation occurs, change to the second programmed channel. Since narrowband and wideband use different filters, if it is the filter, the signal level will jump when you switch to the other filter. With low band equipment, I do not think that you have a narrowband programming option. So what you would see is a loss of sensitivity when the problem occurred.
 

Captain715

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Mar 4, 2004
Messages
107
Location
Columbia, PA
Just out of curiosity: where exactly is the truck when you've had the RX issues? Also, what's the power output and reflected power?

Well to answer the location question is a little tricky, the truck has been moving every time it has occurred, if you are familiar with Lancaster County, PA, the locations have been on the east side of East Lampeter Twp on our way home from a burn in Berks County, on the north-east side of Ironville hill off of Summit Dr, and at the Lancaster County Public Safety Training Center off of Rt 283 in Landisville.

The last time it occurred, we called in to 911 Communications to confirm the Dispatcher we heard was truly transmitting on 33.720 and it was confirmed he was transmitting on 33.720 off of the Williamson Park Tower I believe.

It is rated at 110W, I don't remember the exact measurement at this time.
 

AA4TX

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After rereading your original post, I withdraw my comments. The IF filter will not cause what you are experiencing. Seems rather to be some intermod going on. Sorry for the misdirection.
 

Av8tor56

Member
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Messages
72
Location
Roswell, NM
When you pick them up do you hear just one conversation or several? Does it fade out after a few seconds? Is there any feedback or echoing?
It may be that you're close to the transmitter that you're picking up. If they're off frequency to the low side you may be receiving them due to the range and their power output.
Another possibility is that the dispatcher has "MultiSelect" enabled on the console and is actually broadcasting on two or more frequencies at a given time. Some console systems can do that.
If you can get a watt meter on it and get the true power output and reflected off of the radio it would be a great help. Be sure to have the truck outside, away from any metal buildings or power lines. Have the truck running and the windows up.
 

SWeiss

Member
Joined
Jun 1, 2007
Messages
3
Brian,

I've replied to you elsewhere as requested, I will post here as well for the benefit of the group.

I had a similar problem with a TK-690 low band radio installed in a F-250 p/u. Occasionally I would hear transmissions on another frequency while the radio was on a completely different channel. For example, I would be monitoring (not in scan mode) 33.72 but receive transmissions that were occurring on 33.60.

I had a 1500 watt inverter also installed in the truck. It was mounted inside the work cap (metal cap with side toolboxes, rear double-doors). It was powered via 4 AWG copper cables ran directly to the battery with a inline fuse about 8-10" from the battery terminal. Negative lead also run directly to the battery.

Any time I would turn this inverter on, my radio would exhibit the same symptoms you're experiencing with yours. The inverter was generating severe hash as it was just a cheap, "filthy" (dirty sine wave) unit. Since I rarely used the inverter I never bothered to fix or replace it.


It seems that you have covered just about everything with your radio guy, so here is what I suggest.

1. If you recently installed ANY (yes, anything regardless of how trivial you think it might be) new equipment in the rig, disable it or disconnect it from power to see if the problem goes away.

2. If the problem still persists, or you haven't installed anything new since the problem started, start disabling any electronics in the rig one at a time. This includes ANYTHING, flashlight chargers, portable chargers, radios, laptops, even the AC unit on the roof. Electrically disable (remove the fuse or disable at the load manager) one device at a time. I would start with any type of inverter you have installed. See if your issues continue. If they do, continue disabling each piece of equipment one at a time until you find the culprit.

The problem could entail interference from more than one device. You might have to do some experimenting.

Best of luck!
 
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