FM frequencies cut out by CD player

I've seen good comments about the ST-2, and also about the Crane "Reflect". Check out this thread.

My suspicion is that any decent antenna, placed some distance from the cdp and connected to the tuner via coax, will resolve the interference problem. But obviously an outside above-ground location will provide better reception than having the antenna in the basement.

Hopefully someone else who has experience with specific antennas that may be suitable will comment further. My own antenna is a large roof-mounted directional antenna on a rotator.

Good luck!

-- Al

Thank you for all the information. Since I had never experienced that before I am glad to hear it can be explained by something other than: "Man, that tuner is fried!" I just purchased the tuner and haven't connected an external antenna, just some rabbit ears. It is also in the basement and was wondering if the omnidirectional ST-2 antenna from Dynalab would be a reasonable item. I don't have access to the attic but can place the antenna outside against the house.

How can these two phenomenon be related?

They are not related, they are two separate issues.

RCPrince correctly addressed the issue of crosstalk between inputs that is occurring in the preamp.

Mlsstl offered some good suggestions concerning the issue of rfi from the cdp affecting the tuner. I would add that if you are already using an external antenna, it should preferably be one that is connected to the tuner via 75 ohm coax over the entire run, and not 300 ohm twinlead plus a 300 ohm to 75 ohm adapter at the tuner input.

Most probably the reason for the different behavior above 98.1 MHz compared to below that frequency relates to the fact that 98.2 MHz is exactly 10.7 MHz above the bottom of the FM band (which is 87.5 MHz, although frequencies below 88.1 MHz are not widely used). 10.7 MHz is what is known as the IF (intermediate frequency) that has been used in all FM tuners since the 1940's. What is known as a "local oscillator" circuit in the tuner generates a signal exactly 10.7 MHz below the frequency of the station that is tuned in. The two signals are then mixed together to "beat" the station's signal down to the 10.7 MHz difference frequency, which is then amplified and processed further by the IF circuits in the tuner.

So for stations above 98.2 MHz the local oscillator is putting out a signal within the FM band (above 87.5 MHz), while for stations below that frequency the lo frequency is below the FM band. While I can't offhand formulate a complete explanation of what may be going on, I mention all of that simply to make the point that it is very conceivable that behavior for stations above the 98.1 MHz frequency you mentioned could be different than for stations below that frequency.

Regards,
-- Al

I wouldn't think the problem is preamp input crosstalk. The OP states that the problem is worse above 98.1 MHz on the FM dial and less of a problem below.

Crosstalk would affect all the station frequencies equally since it would be occurring at the analog input stage of the preamp.

On your second question, that is not an unusual occurrence. Cross talk between inputs is common, even among some pricier components (I used to hear it on my Jadis JPL line stage). Way to fix that, of course, is to turn off the component that you're not listening to.

It would appear from your description that the CD player is emitting RFI (radio frequency interference) in the same band the FM stations are using. That's not unusual. Digital devices can be pretty noisy in the radio spectrum.

Are you using an external antenna or the one built into the tuner?

If you are using the tuner's internal antenna, one solution might be to use an external antenna located away from your equipment stand and connect the antenna to the tuner with TV coax cable. (The antenna doesn't have to be outside. 5 or 10 feet from the CD player would likely be more than adequate.)

Tuners are designed to reject a certain amount of noise at the same frequency as the broadcast frequency but there is a limit.

If the external antenna doesn't help, your only other likely solution is to place the tuner itself away from the CD player.