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Old 20th Apr 2019, 11:22 am   #1
Linnovice
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Default Multi Tuner advice

Hi all, in recent months I have accumulated a few fm tuners, four to be precise. I don’t intend on keeping them all but in the meantime like to listen and make comparisons. This means that I am frequently connecting/disconnecting to my pre amp and aerial. This in all reality is a PITA.
Is there a method of being able to connect all permanently and just switch between them?
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Old 20th Apr 2019, 12:50 pm   #2
paulsherwin
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Default Re: Multi Tuner advice

You can connect them all to the same aerial, using splitters or a preamp / distribution amp. The only way to leave the outputs permanently connected is to use a switch box.
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Old 24th Apr 2019, 11:47 am   #3
SteveCG
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Default Re: Multi Tuner advice

Linnovice, I tried using some 'change-over' switches, from both Antiference and Labgear. They were popular in the days of home computers that used the TV as the screen, the idea being that the operator could switch the UHF aerial input of the set to either take the output of the computer or the main aerial. Unfortunately they were 'cheap and cheerful' and I would not rely upon them for making any accurate comparisons.
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Old 24th Apr 2019, 12:27 pm   #4
dave cox
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Default Re: Multi Tuner advice

It depends on what you are trying to compare.

One important parameter, for people more distant from the transmitter, is sensitivity but this best tested using a calibrated RF signal generator / modulator fed directly into the antenna input.

For everything else, use a preamp / distribution amp as previously suggested. You should turn off other tuners for testing as you could get interactions between the local oscillators.

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Old 24th Apr 2019, 12:40 pm   #5
bikerhifinut
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Default Re: Multi Tuner advice

Would it be possible/practical to construct a DIY switching box for an FM aerial?
I was thinking would I lose very much signal through a rotary switch with the coaxial inners soldered to the switch tags? the screens could be all kept connected I imagine, although use of a double pole switch would allow these to be isolated if needed? This would obviate the need for a distribution amplifier and/or a splitter network and cost very little to make, especially if no socketry was involved and use "Flying leads" which would also cut out losses due to using belling lee or other RF connectors? I am of course assuming that only one receiver will be in use at any time.
It would be handy for me in the new room as I could keep the regular FM tuner permanently in place and then it would be a simple matter to switch in any extra ones that I was playing with/fixing up?
Andy.

Last edited by bikerhifinut; 24th Apr 2019 at 12:42 pm. Reason: extra info
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Old 24th Apr 2019, 3:01 pm   #6
G6Tanuki
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Default Re: Multi Tuner advice

Yes you could easily construct a 4-way switchbox for your antenna connection; use a properly screened box (Diecast?), a decent-quality ceramic rotary-switch, and keep the connections between the switch and sockets short, using solid wire (the inner core of some coax offcuts?).

I've done loads of similar things in the past and when tested with 'professional' loss-measuring gear the loss was less than 0.1dB; it also happily handled 50 Watts of transmit-power.

It's up to you whether you contrive to use a second 'wafer' to short the unused outputs to earth ; this is good practice but beware of connecting devices that have a 'power-up-the-coax-to-feed-a-masthead-amplifier' feature as shorting these might not be healthy.

I even made a multi-way switch using the old-style small plastic slide-switches soldered to the inside of a 'box' made from double-sided PCB material. Worked just fine!
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Old 24th Apr 2019, 3:01 pm   #7
ekjdm14
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Default Re: Multi Tuner advice

I think if I were to construct such a switching box for RF, I'd want to have the input and output shield(s) unswitched and all connected to a steel shielding "can" inside which my actual switching of Co-ax signal wires took place. (I'm thinking in terms of modern houses having a lot of RF noise in and around them, so the switch box would be very susceptible to interference creeping in around unshielded signal conductors).

Could be way off, but makes sense in my head! Edit- crossed post with Tanuki
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Old 24th Apr 2019, 6:36 pm   #8
PaulR
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Default Re: Multi Tuner advice

I have a tuner/amp and a separate tuner connected to the same aerial via a simple splitter and they both work well. The aerial was a 3 element one but the front one fell off some time ago but there is still enough signal (I should have insisted on an Antiference when I had it fitted!).
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Old 24th Apr 2019, 10:09 pm   #9
bikerhifinut
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Default Re: Multi Tuner advice

Quote:
Originally Posted by G6Tanuki View Post
It's up to you whether you contrive to use a second 'wafer' to short the unused outputs to earth ; this is good practice but beware of connecting devices that have a 'power-up-the-coax-to-feed-a-masthead-amplifier' feature as shorting these might not be healthy.
If I was to do that i think i would find some good quality DPDT relays and use them to do the switching and grounding. Good point about devices that inject a DC voltage on the aerial to power a masthead amp. This would certainly be relevant as far as our Freeview TV aerial is concerned as at least one of our TVs can feed DC up the wire, mind you it has to be disabled as the antiference masthead distribution amp has its own PSU feeding power "Up the lum". Seems a bit silly to me as if the rigger had to run independent feeds from Aerial to each TV location how hard is it to run a separate supply wire to the box?
As far as FM is concerned its immaterial as I will be using a Ron Smith High Gain aerial and the idea is I won't need any external amplification. The price of living on the wrong side of a fairly steep sided valley in the shadow of the local transmitter!
Anyway I hope the OP gets some good pointers here too. I certainly have.

A.
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Old 24th Apr 2019, 10:10 pm   #10
bikerhifinut
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Default Re: Multi Tuner advice

Quote:
Originally Posted by ekjdm14 View Post
I think if I were to construct such a switching box for RF, I'd want to have the input and output shield(s) unswitched and all connected to a steel shielding "can" inside which my actual switching of Co-ax signal wires took place. (I'm thinking in terms of modern houses having a lot of RF noise in and around them, so the switch box would be very susceptible to interference creeping in around unshielded signal conductors).

Could be way off, but makes sense in my head! Edit- crossed post with Tanuki
Would an extruded aluminium project box do the job? Only I have a couple or 3 plus the odd die cast ally box.

A.
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