Author Topic: transmitting to close to another antenna  (Read 4107 times)

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spacecase0

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transmitting to close to another antenna
« on: April 11, 2016, 08:57:40 AM »
so I left a VX-3R in my shirt pocket and transmitted 5W about 6 inches away (yes, on the same frequency, not like it would matter to much)
now it seems that the receive in tiny HT is not so good anymore,
seems equally attenuated in the HF bands, 6M, 2M, and 440
attenuation is about 5 S units,
so mainly I post this as a warning to others not to do this,

but if anyone knows what part may have got messed up, I would love ideas on what to try changing first
there is a very tiny ESD protector chip right at the antenna input, maybe I fried it ? but the output of the radio is still perfect
maybe I fried the gate of the first mosfet, but would that just make it not here anything at all ?
I just don't have the experience to know the likely cause, and with all the parts so very small, I would rather mess with as few of parts as possible

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Re: transmitting to close to another antenna
« Reply #1 on: April 11, 2016, 09:42:00 AM »
No clue here space.
The only dumb question is the one that did not get asked!!

BTPost

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Re: transmitting to close to another antenna
« Reply #2 on: April 28, 2016, 01:35:17 PM »
I would be looking at the Front-end of the Receiver for a Burnt coil, or blown FET... Typically 5 Watts isn't enough to cause that kind of damage, but close coupling can play funny tricks on receiver Front-ends...  Always remember that RF obeys the Inverse Square Law....
Bruce in alaska AL7AQ

spacecase0

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Re: transmitting to close to another antenna
« Reply #3 on: April 28, 2016, 02:21:01 PM »
I looked for burnt coils and found none,
turns out it is all bipolar transistors in it, (all my mobile radios use some sort of FET)
but they do have protection diodes on the input after the band pass filter stage
so I am thinking I should check there first, and the transistor right after that second
just have not had time to pull it apart again
plus the one by two millimeter parts on every available place is a tad intimidating (I would love a hard copy of the schematic and board layout ), so I have not made time for it, it is planting season now and that just can't wait.

what worries me the most is that it is some cap. that is half broken somewhere in the filter section,
but 5W at 50 ohms is just not very high voltage, so I bet that is not the issue, that is unless the issue has nothing to do with the close transmit I did

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Re: transmitting to close to another antenna
« Reply #4 on: April 28, 2016, 08:26:32 PM »
Should be a FET in there that acts as a pre-amp. That will be blown.
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