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sherwood S7700 III

70.68.7.109
Posted on February 11, 2014 at 13:48:41
robmac63
Audiophile

Posts: 35
Location: vancouver bc
Joined: November 13, 2013
 Guys,I am trying to pick up fm with my receiver.As I turn the dial there's brief music but dosen't hold just drops off instantly.am works fine.
Also for a antenna there is a ground and two fm 300ohm taps.What is the best way to hook this up.
I should know this stuff by now,:(

Thanks Rob

 

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cannot troubleshoot the problem but..., posted on February 11, 2014 at 15:00:03
mhardy6647
Audiophile

Posts: 16013
Location: New England
Joined: October 12, 1999
Contributor
  Since: October 23, 2016
 I (think I!) can help with the antenna hookup.
If you are using an antenna with a 300 ohm balanced line "output" (i.e., flat "twinlead" wire) - use the two 300 ohm taps.

The ground should be for an external AM antenna, or IF there's a 75 ohm unbalanced FM input, that would be for the 'shield' of the 75 ohm coaxial cable from the antenna.

If you have an antenna with a 75 ohm unbalanced "output" (the aforementioned coax), and there are only 300-ohm antenna connections for FM, you'll need a 75 to 300 ohm "balun" (balanced to unbalanced) impedance matching transformer (if you don't have one already). This should still :-) be available at Radio Shack or maybe (???) even Home Despot.

Hope this helps!

all the best,
mrh

 

RE: cannot troubleshoot the problem but..., posted on February 11, 2014 at 19:26:53
robmac63
Audiophile

Posts: 35
Location: vancouver bc
Joined: November 13, 2013
 Thanks for the advice.Will get the antenna working once I find the fm issue,might be outta my leauge.Other than testing the tubes and maybe some resoldering.So for now just really enjoying the phono stage.

Rob

 

RE: cannot troubleshoot the problem but..., posted on February 11, 2014 at 20:03:50
robmac63
Audiophile

Posts: 35
Location: vancouver bc
Joined: November 13, 2013
 Wow fm is working now.All I did was move the ferrite antenna around.I will still make a proper antenna.
Thanks again!!
Rob

 

The ferrite antenna has nothing to do with FM reception., posted on February 13, 2014 at 09:32:18
Timbo in Oz
Audiophile

Posts: 23221
Location: Canberra - in the ACT - SE Australia
Joined: January 30, 2002
 It's a resonant device designed to approximate a 300 metre long wire.

FM signal's wavelength is 100 times shorter than that. A good FM antenna is not a simple matter. For good reception in stereo an FM receiver's front-end needs to be driven into full limiting on - all - your desired stations, by a strong signal free of multi-path (reflections of the signal from the surrounding buildings and hills.)

This is particularly important with stereo FM because the component necessary to decode stereo (a Left minus Right remnant on a separate carrier) is not strictly an FM signal, but more like an AM Single-Side-Band transmission.

A directional antenna with gain is almost always essential. Good reception of stereo FM transmission is highly directional - the best antennas for FM are largish directional external types (boom and cross-elements) on a mast or one mounted in a loft.

OR an internal DIY wire rhombic on the floor/ceiling or in a loft. Click below for the article.

You will need to find out where your desired FM stations are in relation to your residence. Try the FM Fool web site for US stations.

IF signal strengths are high where you are an indoor directional antenna might be good enough. Don't get an amplified one - reception with these is usually very noisy. Try rabbit ears - at Radio Shack / Tandy OR a simple T antenna from say C. Crane.

The best indoor antenna is a rhombic if you have room, and all your stations are in one main direction. You make it yourself from 300 ohm twin ribbon, some loading resistors, a balun into some coax down-lead to the tuner.






Warmest

Tim Bailey

Skeptical Measurer & Audio Scrounger


 

RE: The ferrite antenna has nothing to do with FM reception., posted on February 13, 2014 at 09:59:03
robmac63
Audiophile

Posts: 35
Location: vancouver bc
Joined: November 13, 2013
 Great advice Timbo thank you.I have bits and pieces at home to do a roof top antenna.also have a motor for turning it.I will get a alignment done first then look into either building one or possibly buying a good one?.

Cheers Rob

 

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