Subject: Re: Has anyone looked into upgrading the SSB/CW filter or front end for HF?
Newsgroups: gmane.recreation.radio.hardware.kenwood.th-f6a
Date: 2008-04-15 05:24:01 GMT (11 weeks, 4 days, 18 hours and 20 minutes ago)
Hi Michael, A couple of comments. Remember this is a handheld radio. It can't have the performance of a larger radio for several reasons. Simplifying greatly, Selectivity generally equals filter size. Front end performance is also size (for filtering) and power consumption (for overload performance). Plus, as I recall, front end filters are low and or high pass. Therefore strong out of band signals may still be in teh front end bandwidth. I haven't studied the schematic and don't know what kind of filters are used - I would guess ceramic. Probably other filters could be swapped in, and this may help get better single signal reception. However, overload is another matter of the RF amp and mixer design. Another big factor in receiver selectivity is also size in regards to both the front-end IF areas because having the filter input and output close together makes it difficult to isolate them and, as a result, signals sneek around the filter limiting the far out attenuation. A tuner could help. Size does matter here. (:o) Also a note on terminology. I completely understand (as I am sure others do) what you are saying about sideband suppression. However, what you want is classiclly called "Single Signal Reception". The BFO is placed on or outside the edge of the filter so you only hear a beat (CW tone) on one side of zero beat. Perhaps you also noticed that the 33Hz steps are not uniform. This is because they are not synthesizer steps, but rather an oscillator that is shifted by adding/subtracting capacitance; and this is not very precisely done. 73, Steve, K9DCI --- In TH-F6A@..., "d121075" <kg4kri@...> wrote: > > Hi Michael, > > Thanks for the response! The problem is with strong signal overload, > combined with mediocre opposite sideband suppression. The opposite > sideband suppression is adequate for casual listening, but with an > outdoor antenna connected, the image frequency of the opposite > sideband breaks through more than I would like. The CW filter, which > just seems to add narrow audio processing to the LSB setting, > sometimes helps. I just would like to put a little more selectivity in > there- to stop some of the blow-by that is letting the opposite > sideband get through when the band is busy. For the time being, I am > going to hook up an antenna tuner to deal with some of the overload on > 40 from the broadcast stations, and also a resistive attenuator to > back off the raw signal being presented to the front end from the > outdoor antenna. > One of these days, when I get brave enough, I am going to try to add > another crystal filter to the radio. > > Daniel, KG4KRI > --- In TH-F6A@..., Urantian <oneurantian@> wrote: > > > > Hi Daniel, > > > > I use the radio a lot for HF listening and I haven't had trouble > with CW. I'm using a Miracle Ducker IL with a telescoping antenna. > It's a great combination for one-handed portable use. I have great > reception from 80 through 17 meters. > > > > Are you using the CW mode setting, or USB/LSB? Or, is the trouble > with selectivity, in which the passband is too wide, and you are > hearing multiple signals? > > > > ---Michael, NO6O > > > > > > > > > > ----- Original Message ---- > > From: d121075 <kg4kri@> > > To: TH-F6A@... > > Sent: Saturday, April 12, 2008 9:46:48 PM > > Subject: [TH-F6A] Has anyone looked into upgrading the SSB/CW filter > or front end for HF? > > > > I am a new member, and I have had this great little radio for about > > four years. I use it the most sitting at night listening to 80 and 40 > > meter cw with an external antenna, and I wish that I could modify the > > sideband filter to get a little more rejection of the opposite > > sideband, or maybe put in a roofing filter in the IF to reduce some of > > the front end overload. I may be asking too much of this little ht, > > but single-signal reception sure would be nice! Has anyone in this > > group experimented with hf reception and the radio? > > Thanks, > > Daniel > > KG4KRI > > > ------------------------------------