JoinTenna Info (about $30+s/h):http://www.channelmaster.com/Pages/TVS/Passives.htmhttp://www.warrenelectronics.com/Ant...Jointennas.htmhttp://www.hdtvprimer.com/ANTENNAS/GlossaryG.html
It is basically a two-way antenna diplexer/combiner, where the single channel input
goes through a narrow bandpass filter which attenuates all except the "chosen" channel.
The wideband all-channel input (the one you want to use) goes through a notch filter that is tuned for maximum attenuation of the visual carrier.
Note that you order it for a particular channel number, which requires the vendor to tune the filters for the desired UHF channel prior to delivery.
The all channel input also attenuates (to a lesser degree) adjacent channels (CH22, CH23 and CH25)
and will have only a small attenuation against CH21 and CH26.
Hence, you might want to consider inserting an additional JoinTenna tuned for CH26.
Unfortunately, the notch will only be effective against a relative small portion of the DTV signal spectrum,
which is spread across the entire 6 MHz channel allocation.
You might think that the analog CH24 (1320 kW peak power) would be more of an overload problem than digital CH26 (440 kW average power).
However, the PEAK power is what causes preamp overload (just like in any other kind of amplifier).
And the PEAK power of a DTV signal is about 7 dB higher (2200 kW peak power):http://www.avsforum.com/avs-vb/showt...ak#post6268128http://www.avsforum.com/avs-vb/showt...ak#post6273553http://www.avsforum.com/avs-vb/showt...ak#post6290253
To give you an idea on how ineffective a single notch filter might be,
look at the attenuation curve for the following Eagle Notch Filter from tonercable:http://www.tonercable.com/Toner%20We.../EAGLELITE.pdf
Each horizontal subdivision is 1.5 MHz, so the notch will be very effective against the visual carrier,
but will have very little attenuation against the aural carrier located 4.5 MHz higher.
Fortunately, the station broadcasts the aural carrier (typically) 13 dB below the visual carrier for an analog NTSC signal.
Note that since the visual carrier is at the bottom of the NTSC channel (see picture),
the notch attenuates the lower adjacent channel much more than the upper adjacent channel.
You could accomplish a somewhat more effective attenuation (esp against DTV) by ordering double narrow-band notch filters.
Winegard UT-2700 (about $40+s/h) has two separate traps, one tuned for the visual carrier and the other for the aural carrier frequency.
This would be much more effective than a single trap, especially against a digital channel that does not have distinct energy peaks:http://www.winegard.com/offair/trapsfilters.htmhttp://www.epinions.com/content_190042771076
[Note that the picture is for a Mulitswitch, not the UT-2700.]http://www.summitsource.com/product_...oducts_id=5344
Blonder-Tongue makes the (ouch, $220+s/h) MWT series of narrow-band notch filters that also have two separate tunable traps:http://www.solidsignal.com/prod_disp...T=&PROD=SS4614http://www.starkelectronic.com/btc15-1.htm
All of these filters claim to have a minimal 0.5 dB of insertion loss in the UHF band.