BCD996XT not receiving

[loumaag]

Originally Posted by ST-Bob

Well there are transceivers like the Yaesu FT-8900 which can do cross-band repeat that have a VHF transmitter in the same box using the same coax connector and antenna as a UHF receiver (and vice-versa) so there's no technical reason why a nearby transmitter should blow out a receiver... If you can have them both in the same box then separating them by a foot or two with different antennas should present far less voltage at the receiver than having them sharing an antenna would.
...

Bob,
I think you miss the point that a dual band transceiver capable of cross-band repeat has an internal duplexer (or is it a diplexer) that keeps the two bands separate. Try putting both sides on the same band and transmit on one side and the other side is automatically switched out/off so that no damage can occur. Have you ever sat in a parking lot having an eyeball QSO with someone and either he or you got on the local repeater; notice that your radio probably couldn't hear him (on the repeater output) because of the desense? Keep that up and damage will eventually occur.

Let's also remember that transmitting on HF, even at real power (say 500 W or above), is not going to affect the front end of a VHF or above receiver/scanner because the front end of those are specifically designed to ignore below 30 MHz signals.

[MikeOxlong]

Originally Posted by loumaag

duplexer (or is it a diplexer)

Duplexer = Transmit\Receive filtering
Diplexer = Band filtering

The radio would have a built in diplexer to keep the bands separate.

[tilt404]

Just trying to figure out now how not to damage my future and current scanners. All I have now is a 5w dual band handheld ham radio (144/440). I usually transmit at 2.5w-0.5w while sitting at my desk. My Uniden BCD996XT is at my desk but will be connected to a Comet discone on the balcony about 15 feet away. My GRE PSR800 is also at my desk with a Watson W-881 antenna on it.

So even talking on the HT using 2.5 to 0.5w I should shut off the GRE then? It's usually only scanning a 800Mhz trunk system.

For the Uniden connected to the discone outside, I should also shut it off too while transmitting?

Just asking since I want to be safe and these scanners aren't cheap. I was thinking that I would get a antenna switch so I could transmit on the discone and receive, switching it between the Uniden and HT. But my trouble is that its hard to find a antenna switch that has spec's higher than 500Mhz. The ones I had in the past from Daiwa usually only to as high as 600Mhz, so I would lose out on receiving the 800mhz trunk systems?

I thought the switch would of been nice since then it would bypass the uniden scanner when I'm transmitting on the HT hooked to the discone. Sometimes in special occasions though like black outs and fires and other events, I monitor the GRE scanner while talking on the ham radio. Usually monitoring 800Mhz on the scanner and talking on UHF 400Mhz. I'm not even sure if this is safe to do?

[tilt404]

don't know why every time i post, it posts twice..? just had to delete this one again

[Hooplahpro]

Greetings,

Thur Oct 18th the BCD996XT scanner was returned to me from the Uniden Service Center in Texas with the following information. Note that the repair was covered under the warranty.
__________________________________________________ ___

THE FOLLOWING PARTS WERE REPLACED OR ACTIONS PERFORMED DURING THE REPAIR OF YOUR UNIT.

D13, D26, D51, D52, Q4, Q5

THE FOLLOWING NOTES(S) PERTAIN TO THE REPAIR OF YOUR UNIT.

CHECK CONNECTIONS ON EXTERNAL ANTENNA. IF THE UNIT IS CLOSE TO A TRANSMITTER, MAKE SURE SCANNER IS NOT RECEIVING THE SAME FREQUENCY BEING TRANSMITTED.
__________________________________________________ ___

Thus this confirms that transmitting close to this scanner took out four diodes and two transistors.

While I never listened to the same frequency on the scanner as I was transmitting on, I would suggest that there are combinations of frequencies that would allow this to happen. For example in CB radio transmitting on 27.405 Mhz, a 1st harmonic is generated at 54.910 Mhz. As TV channel 2 is 54 - 60 Mhz, a TV close enough to the CB would lose the video signal per receiving the 1st harmonic signal from the CB.

Given two outside antennas, one for transmitting an the other for scanner receive...
The complexity of trunking systems...
The thousands of frequencies Amateur radio operators are allow to transmit on...

I would definitely suggest putting in a manual antenna switch on the scanner to disconnect it from the scanner antenna when transmitting.

But working in electronics for twenty years, I'm thinking do it electronically! Most modern Amateur radios can connect to computers and have logic signals when a transmission is in progress. Thus route this signal to a relay which activates an electronic antenna switch to break the antenna connection, then reconnect when transmission is complete.

I suspect someone has thought of this idea before, but if not, here's your chance to design, fabricate, production, distribution, and become extremely rich!!!

Regards,
George

[MikeOxlong]

I think most people are cheap and would just separate their antennas by a few more feet when doing the initial installation.

[cknizeski]

Originally Posted by Hooplahpro

I suspect someone has thought of this idea before, but if not, here's your chance to design, fabricate, production, distribution, and become extremely rich!!!

Ramsey makes an RF relay kit that can disconnect an antenna when you transmit.

RFS1 - RF Sensed T-R Relay Kit - Ramsey Electronics

[tilt404]

I've been trying to make sure to shut off and even disconnect the antenna from my PSR800 scanner while I talk on my Yaesu FT60R ham radio transceiver. Even though I just use 0.5-2.5w typically to transmit, I still worry after reading this post. The antenna, a discone for the scanner is outside on the balcony and I usually talk on the HT inside using its whip antenna. I don't have the same frequencies in the scanner that I talk on, but some I scan are in the same band. I don't know if you are aware of the power levels you used that caused the damage, but I guess nothing is truly safe.

I still see so many vehicles with many antennas, side by side on the roof, everything on inside. Transmitting, receiving... Wondering about the damage. Makes me never want to buy a used radio ever again.

[loumaag]

Originally Posted by MikeOxlong

I think most people are cheap and would just separate their antennas by a few more feet when doing the initial installation.

This describes my method, cheap and effective.

I have been doing it for years; although, to be honest I have, in the past, mounted the scanner outdoor antenna right at the top of my support for a inverted V with no ill effects. Of course I seldom (read almost never) use 10 meters and and no scanner I ever had hooked up this way suffered from 80/40/20 meter operations at 450 watts yet.