436/536 RF overload from nearby ham radio damage resulting in receiver fail. Q2 and Q3

[mancow]

I have a BC536HP co-located with a repeater site. It has been there probably 4-5 years. A 125 watt 4 bay vhf and a 125 watt 16 bay uhf plus a 75 watt 6 meter. The receiver is on a discone about 12 feet away. Zero issues. I now have an SDS200 up there and still no issues. Did the antennas actually touch?

 

[radioman2008]

I have a BC536HP co-located with a repeater site. It has been there probably 4-5 years. A 125 watt 4 bay vhf and a 125 watt 16 bay uhf plus a 75 watt 6 meter. The receiver is on a discone about 12 feet away. Zero issues. I now have an SDS200 up there and still no issues. Did the antennas actually touch?

no. but i was using multiple radios on my car, fusion VHF/UHF aprox 40 watts motorola XTL5000 UHF aprox 45w and the probable culprit....110w VHF astro spectra. the scanner antennas were all within 2-3 foot of the radios.
i have an SDS100 and it does not seem to have been affected, and it was one of the scanners in the group
this is not the first time i have lost rx on one of my unidens. now i realize why.
no more transmitting on ham radios when the scanner antennas are on the roof.

 

[mancow]

Oh, 110W Astro. Yea, you had a BBQ.

 

[Ubbe]

There are protection diodes at the antenna port that limits the voltage to 1,4V, but those could have been fried and either go open or partially or fully conduct and shortcircuit the signal, but then you have bandfilters prior to any active transistors. Only if you are scanning the same frequency band will it pass enough signal to be able to damage any transistors. If you need to transmit at VHF, then set the scanner to a UHF frequency and it will attenuate the signal to at least a 100 times lower.

Two antennas 2ft apart attenuates only 10dB so 110W are 10W at the scanners antenna connector, if the antennas have matching frequency bands. That's 60V p-p and 1 ampere to the protection diodes that will fry them. After the bandfilter the signal are reduced to 0,6V. If the same band filter are selected in the scanner that matches the transmit frequency then the transistors input will be exposed to the full 60V.

/Ubbe

 

[Remon]

You would have to be really close to the transmitting antennas to receive any damage like less than 10ft away.

If someone keys up the local 70 cm ham repeater (1.5 miles away) and I look at my sdr, I see tons of overload. Even with the gain set to zero. In comparison: when I transmit with a licence free UHF radio close (less than 10 feet) to my SDR antenna it doesn't overload that bad..

The ham repeater tx antenna is nearly on top of a 1200 feet tower with directional antennas pointed at me. I can hear it across all bands. It's like it does enter the mixing stage of my scanners and receivers.

I gave up on the 436/3600.

 

[Remon]

There are protection diodes at the antenna port that limits the voltage to 1,4V, but those could have been fried and either go open or partially or fully conduct and shortcircuit the signal, but then you have bandfilters prior to any active transistors. Only if you are scanning the same frequency band will it pass enough signal to be able to damage any transistors. If you need to transmit at VHF, then set the scanner to a UHF frequency and it will attenuate the signal to at least a 100 times lower.

Two antennas 2ft apart attenuates only 10dB so 110W are 10W at the scanners antenna connector, if the antennas have matching frequency bands. That's 60V p-p and 1 ampere to the protection diodes that will fry them. After the bandfilter the signal are reduced to 0,6V. If the same band filter are selected in the scanner that matches the transmit frequency then the transistors input will be exposed to the full 60V.

/Ubbe

What if Close Call is enabled? Does the set to other band trick still works?

 

[prcguy]

If someone keys up the local 70 cm ham repeater (1.5 miles away) and I look at my sdr, I see tons of overload. Even with the gain set to zero. In comparison: when I transmit with a licence free UHF radio close (less than 10 feet) to my SDR antenna it doesn't overload that bad..

The ham repeater tx antenna is nearly on top of a 1200 feet tower with directional antennas pointed at me. I can hear it across all bands. It's like it does enter the mixing stage of my scanners and receivers.

I gave up on the 436/3600.

At 1.5mi distance and at 70cm there is about 93dB of free space path loss. With 100w reaching a 10dB gain antenna to a Discone within the transmit antennas radiation pattern at your place I would expect a signal level around -33dBm not counting some other variables. -33dBm is a pretty strong signal but it can't hurt any radio. That along with some other strong signals can certainly create IMD in a mediocre receiver.

 

[radioman2008]

I see various names for what this package transistor operates as
can you tell me what the specific type of transistor goes in this RF position?
these are all names of various transistor configurations listed under this package design.
1. Zener diode
2. motorola part MRF9411LT1 says Designed for use in high gain, low noise small–signal amplifiers.
3. p channel mosfets
4. switching diodes
5. Schottky diodes
6. Linear voltage regulator

 

[Ubbe]

What if Close Call is enabled? Does the set to other band trick still works?

Close Call has to enable the proper band filter when its active, so if you have selected CloseCall to work in the VHF band then it has to enable the VHF band pass filter.

/Ubbe

 

[Ubbe]

I see various names for what this package transistor

It's more of the #2 Motorola type but that goes up to 8GHz so probably unnecessary expensive and probably works worse at lower frequencies than a transistor that only goes up to 1GHz. It has to be capable of handling high level signals without loosing performance.

/Ubbe

 

[radioman2008]

It's more of the #2 Motorola type but that goes up to 8GHz so probably unnecessary expensive and probably works worse at lower frequencies than a transistor that only goes up to 1GHz. It has to be capable of handling high level signals without loosing performance.

/Ubbe

mouser has a list of BAV23 components, can you take a look thru these and help me identify one that would work. ive looked at some but dont know all the variables.

https://www.mouser.com/c/?q=BAV23

 

[Ubbe]

mouser has a list of BAV23 components, can you take a look thru these and help me identify one that would work. ive looked at some but dont know all the variables.

https://www.mouser.com/c/?q=BAV23

It's probably easier to google up the guy who replaced his transistors and got better performance, that are proven to work and work better than the originals.

/Ubbe

 

[radioman2008]

It's probably easier to google up the guy who replaced his transistors and got better performance, that are proven to work and work better than the originals.

/Ubbe

ive spent over an hour searching/reading google with all the following key words in various combinations.
BCD436HP/BCD536HP/SDS100/SDS200/Q2/Q3/Transistor/replacement/mod/modification/improvement/hack/overload/no RX/
google usually points me back to radio reference. ive read, probably 20+ threads, probably looked over 100 or more responses.
theres quite a few that people recognize they have lost reception, but no info as to why, some say its also a thing on other uniden scanners.
some recognize the scanner has been damaged by overloading RF, some talk of sending it in for repair and reference the Q2 Q3 were replaced.

scanner.ru is down

my post has the most in-depth commentary to this problem than any other post i could find.

unfortunately, i can't find the post you reference, both in and out of radio reference.

 

[radioman2008]

found this datasheet for same looking package different term SOT343
50mhz-4ghz, better than 8ghz (might not be best due to scanner going down to 25mhz)

https://www.mouser.com/datasheet/2/412/SPF5043Z_Data_Sheet-1500773.pdf

45mhz-6ghz (might not be best due to scanner going down to 25mhz)

https://www.mouser.com/datasheet/2/1030/SAV_541_2b-1701364.pdf

50mhz-6ghz (might not be best due to scanner going down to 25mhz)

https://www.mouser.com/datasheet/2/196/bga622-59816.pdf

unsure

https://www.mouser.com/datasheet/2/196/Infineon_BGA616_DS_v02_01_en-3160354.pdf

https://www.mouser.com/datasheet/2/196/Infineon_BGA427_DS_v01_01_en-3160339.pdf

https://www.mouser.com/datasheet/2/196/bga420-56450.pdf

DC-2.4ghz?

https://www.mouser.com/datasheet/2/196/BGA614-74226.pdf

 

[Ubbe]

I thought it was scanner.ru but it is www.radioscanner.ru
The original Q2 are a BFP420
I will search some more about the better working substitute transistor.
The russian forum are very interesting as they usually have problem to buy things and they instead invent their own solutions.

/Ubbe

 

[dave3825]

The russian forum are very interesting as they usually have problem to buy things and they instead invent their own solutions.

Seems they also like to modify the firmware.


Was this by chance something you saw? It does not mention Q1 or Q2 but does mention BFP420

BCD436HP, BCD536HP. Uniden анонсирует свою новейшую флагманскую линейку сканирующих приемников - Страница 63

 

[Ubbe]

Sometimes the amplifier transistors are Q1 and Q2 and other times it's Q2 and Q3 and the AGC regulator transistor for AM mode are Q1 or Q3 depending of scanner model. The BC125AT have the first transistor being BFP420 and the second a cheaper one. The BCD325 and upwards in models have both transistors being BFP420. They are 45 cent a piece and the whole SDR receiver in SDS scanners are 85 cent, so there are a significant cost reduction for the receiver in SDS scanners. But then the big color display cost more than a smaller B/W one and the software development to handle the SDR receiver are extra, but then it is the same one used in both SDS100 and SDS200 so they share the cost and the operating system and functions and features comes from the BCDx36 scanners that we already have financed.

The euro distributor www.avera.eu has some scanner schematics for download and part lists. The BFP420's part# are BDBN1150001 and Avery sell those for €3

/Ubbe

 

[radioman2008]

Sometimes the amplifier transistors are Q1 and Q2 and other times it's Q2 and Q3 and the AGC regulator transistor for AM mode are Q1 or Q3 depending of scanner model. The BC125AT have the first transistor being BFP420 and the second a cheaper one. The BCD325 and upwards in models have both transistors being BFP420. They are 45 cent a piece and the whole SDR receiver in SDS scanners are 85 cent, so there are a significant cost reduction for the receiver in SDS scanners. But then the big color display cost more than a smaller B/W one and the software development to handle the SDR receiver are extra, but then it is the same one used in both SDS100 and SDS200 so they share the cost and the operating system and functions and features comes from the BCDx36 scanners that we already have financed.

The euro distributor www.avera.eu has some scanner schematics for download and part lists. The BFP420's part# are BDBN1150001 and Avery sell those for €3

/Ubbe

thank you. just purchased a small quantity of BFP420 for testing, some fine tip solder tips for my low wattage iron, a stand with magnifying glass, so im going to do this and see what happens and ill let everyone know the results.

 

[dave3825]

I put mine back together so if you happen to see the real time clock batt, please post a pic since I forgot to look. Also was going remove my lcd screen to see if there was any part numbers on the back but did not have my iron where I was.

 

[zhenya_yalta]

https://www.infineon.com/cms/en/product/rf/rf-transistor/low-noise-rf-transistors/?redirId=191261