Addition of filters in the receive line.

VK4BXI
Posts: 62
Joined: Sat May 22, 2021 11:44 am
Location: Brisbane

Addition of filters in the receive line.

Postby VK4BXI » Mon Sep 20, 2021 2:55 am

Hi all, I have a local community radio transmitter running on AM close to me. Its coming in at ~0 dbm ! on 1.5MHz on my long wire. On my Flex 5000A I run a notch filter that can be inserted into the receiver line with the TX/RX switching handled inside the rig. I have looked on my 7000 mk II and don’t appear to have the same feature.
Please can someone advise me how to handle this. I can if I have to install a pair of relays around the notch filter and use an output from the rig to switch them. I could I suppose upsize the filter so that it will take transmit power but that would be a chunk of work.
All suggestions (no rude ones please ) gratefully received.

Regards Bob VK4BXI
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w-u-2-o
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Re: Addition of filters in the receive line.

Postby w-u-2-o » Mon Sep 20, 2021 12:25 pm

Sadly, this is not possible on the 7000. Or, for that matter, on the 8000, or any 100D or 200D that uses a Rev. 24 RF board. It remains possible on older 100, 100D, and 200D units with Rev. 15 or 16 RF boards.

Rev. 24 and subsequent designs gave up that switching path in order to provide better support for PureSignal external feedback.

However, you do not have to go the route of installing external relays. Simply open up the 7000 and install the filter on the Orion MKII RX1 input, between the RF board output to RX1 and the Orion MKII itself. I believe it is J13 on the RF board and J5 on the Orion MKII, but you will have to double check that, I don't have a 7000.

If the filter won't fit inside, then you can find a way to route coax externally. Either way it'll be a hell of a lot easier than building and controlling a high power relay unit.

Don't forget this will not protect the RX2 receive path when RX2 is assigned to the second ADC.
VK4BXI
Posts: 62
Joined: Sat May 22, 2021 11:44 am
Location: Brisbane

Re: Addition of filters in the receive line.

Postby VK4BXI » Mon Sep 20, 2021 8:36 pm

Thanks for that. I had a good look at the over view drawing and couldn’t see a switching path that would work. I suspect that my best plan would be when I get up enough nerve to open up the box, to add two SMA sockets in the back and loop the RX 1 signal through them. Then adding my “ugly” filter in that loop.

Regards Bob VK4BXI
K1LSB
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Re: Addition of filters in the receive line.

Postby K1LSB » Mon Sep 20, 2021 11:00 pm

Bob,

Exactly what problem is the strong AM signal causing? I also am very close to several very strong (+3 dBm) stations but it's not a problem for my 7000. I just dial in 15dB or so of S-ATT when I'm on the L/MW band so the front end doesn't overload. If I'm in the 160 meter ham band (or any of the other ham bands for that matter) I see no deleterious effects from the BCAM stations at all, even with 0db of attenuation.

I guess I don't understand what needs "handling".

Mark
VK4BXI
Posts: 62
Joined: Sat May 22, 2021 11:44 am
Location: Brisbane

Re: Addition of filters in the receive line.

Postby VK4BXI » Mon Sep 20, 2021 11:39 pm

Understood Mark,
yes you are correct some att (20db in my case) in the front end does “cure” the problem. It was only that I had gone to the trouble before to make the filter and install it previously . I was very comfortable with having fixed the problem “correctly” in that I had not reduced the front end sensitivity of the radio (the flex 5000A is good but not in the same league as the 7000). I assumed that this kind of arrangement (being able to insert a filter in the RX line) would be a “standard” feature of a top rig. But as explained above getting P.S. to work properly was (and I agree) more important.
I do go down to the L/MW band from time to time….mainly to monitor this particular station ! The station is a small setup and always challenged to get a good signal out……..so they frequently can be found running twice their allowed bandwidth and heavily over driven in the hope of reaching more people ( and more revenue ). The net result is unpleasant and ends up in the 160 meter band more often than not. I then have to be very certain that its the station causing this and not my own rig front end over loading before making complaints.

Regards Bob VK4BXI
K1LSB
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Joined: Wed Feb 05, 2020 5:25 pm

Re: Addition of filters in the receive line.

Postby K1LSB » Tue Sep 21, 2021 1:09 am

Rob,

Understood, thanks for clarifying.

Mark
K1LSB
Posts: 639
Joined: Wed Feb 05, 2020 5:25 pm

Re: Addition of filters in the receive line.

Postby K1LSB » Tue Sep 21, 2021 1:09 am

K1LSB wrote:Bob,

Understood, thanks for clarifying.

Mark

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