Using Hotspots in close proximity to one another

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G0APM
Posts: 16
Joined: Tue Dec 11, 2018 11:10 pm

Using Hotspots in close proximity to one another

Post by G0APM » Sun Feb 17, 2019 1:45 pm

I seem to be collecting Hotspots for some reason, you can never have too many I suppose!
There's a simple calculation: N + 1
N being the number of radios you already have plus another.

I have 3 ZUMspot hats in fairly close (6") proximity to one another, C4FM, D-Star & DMR, all on different
frequencies of course and about 4MHz apart. I'm wondering how susceptible they are to desense?
I've noted unexplained drop-outs from time to time, I don't suppose the RX 'front ends' are tuned that
much, or at all.

So I've cranked the 'RFLevel' down to 10 on them all and I'll see what happens. The original value is/was
100. I'm unsure how this value, and changing it, adjusts O/P power?

Anyone else experienced problems with close by devices?
73 - Clem - G0APM - always tinkering
CO of Essex in the SE of England

K9EQ
Posts: 20
Joined: Wed Jan 09, 2019 4:07 am

Re: Using Hotspots in close proximity to one another

Post by K9EQ » Tue Feb 19, 2019 11:55 pm

The receivers are total garbage. They also make great mixers. I solve most of my problems by placing a 6-10 dB attenuator between the hotspot and the antenna. You can find SMA attenuators that will work well.

The DV4mini placed a 6 dB attenuator on the PCB, which is the right thing to do. I have yet to see any of the other hotspots (including OpenSpot) do the same.

Also try to select frequencies that are not related in any mixing scenario. So 444.000, 444.025, and 444.050 would be a very bad idea.

73,
Chris, K9EQ

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G0APM
Posts: 16
Joined: Tue Dec 11, 2018 11:10 pm

Re: Using Hotspots in close proximity to one another

Post by G0APM » Fri Feb 22, 2019 7:20 pm

Thanks Chris.

Putting an attenuator in line is a great idea, I'll do just that :) .. 10dB seems a good level, I'm never too
far away from the Hotspots.

Time to look on Amazon / Ebay.

73 my friend.
73 - Clem - G0APM - always tinkering
CO of Essex in the SE of England

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VK7HSE
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Joined: Sun Apr 15, 2018 6:35 pm
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Re: Using Hotspots in close proximity to one another

Post by VK7HSE » Sat Feb 23, 2019 5:55 am

An alternative is if you have two on DMR is to enable private mode and use a different CCS7 number per hotspot this way they will only respond to CCS7 ID they have been setup for but they will still suffer desence from the other hotspot. The only way to circumnavigate that would be to insert a notch/pass through filter per unit. These usually get called a duplexer! But really they're a R/C filter Image

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KB0OXD
Posts: 39
Joined: Mon Jun 18, 2018 9:51 pm

Re: Using Hotspots in close proximity to one another

Post by KB0OXD » Thu Jul 04, 2019 4:26 am

For something like this, I'd use DIFFERENT bands, frequencies, rooms (WALLS make GREAT RF attenuators at times) & ANYTHING ELSE I can think of :)

Cheers & 73 :)

Pat, KB0OXD

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