Just checking on unanswered postings and came across yours and although not an expert on SDR I'll do my best to provide whatever help I can.
I see you have a 6900 CB radio listed on your equipment so do you have this setup as a home base unit or mobile?
The reason I ask is that if you have a home base antenna
you could try hooking it up to your SDR and see if you get any improvement on reception compared to whatever antenna
you currently use for it.
You're bound to come across arguments that it will 'overload' the front end of the SDR, (signals too strong), but others will argue the resonance of such an antenna
will improve reception to those frequencies of interest. I'm with the latter argument only because most of the web based SDR sites that tune CB frequencies tend to utilise a CB antenna
for such activities. (A simple half wave CB antenna
seems to be popular.)
You don't state as to why you want to make such a setup but I have seen examples where a SDR is used to scan the bands on home base antennas and when activity is found they use an antenna
switch, (manual or automatic), to switch over to their transceiver to then broadcast to what they were hearing. Sort of like putting a pan-adapter onto a radio that doesn't have one. I can also see it as a handy thing to check the CB bands for activity due to propagation as the 'mid-band' or often used European frequencies see activity way before the usual 'triple 5', (27.555MHz).
You'll probably find a CB antenna
setup will improve your SDR reception on other frequencies too compared to the tiny antennas usually used on such setups.
Anyway, 'batting it out there' for you more than anything else. I hope you find a solution for what you are trying to do.
If anything it's peaked my interest in giving me thoughts on a SDR to scan Amateur 2m VHF activity on my own setup. That way I won't have four radios on the go checking two repeaters, FM and SSB calling frequencies!!!
All the best,