Reddit mentions of Verizon Home Phone Connect F256VW External Yagi Antenna 18db 800mhz 850mhz 900mhz 1800mhz 1900mhz

I am liking the possibility of a passive repeater, particularly the relatively lower maintenance.

If, hypothetically, we used two of these antennae:

https://www.amazon.com/Verizon-Connect-External-Antenna-1800mhz/dp/B00D19KH6E/ref=sr_1_5?s=wireless&ie=UTF8&qid=1521302674&sr=1-5&refinements=p_n_feature_keywords_browse-bin%3A8067600011%2C4041828011

...and connected them with a short length (1-3 feet, depending on what I can get) of cable, is there a way to estimate the anticipated signal strength at camp?

Let's assume a -60 to -65 dB signal at the top of the hill. It may be even better, but I'm trying to be conservative. The top of that hill has direct, unimpeded line-of-sight to the cell tower 7.3 km away.

The antennae claim a 18 dB gain. I am a little wary of that claim, since vendors tend to be a little overenthusiastic, but let's assume half that. So, 9 dB gain. Since we are using two of these antennae back to back (one pointed at the cell tower, and one at camp), would the net gain be effectively doubled? Or do they not "stack?"

In any case, whatever the compound antennae gain is -- if the antenna gain is greater than the cable loss, the net result should be bending a usable signal over the hill, right?

I used this online tool to estimate cable loss:

http://www.qsl.net/co8tw/Coax_Calculator.htm

For a short length (3 feet) of RG-58, unpowered, it gave me a dB loss of less than 1 dB. I tried other cable types, too, and they all resulted in less than 1 dB signal loss.

Still need to figure open air path loss for the hop from the hill to the camp. The distance is 1.3 km.

I know that the signal from the cell tower is still usable at the overall distance of the camp, because there is another large hill even further away from the cell tower than the camp is, and we can get a signal up there, too. So, again, the key seems to be the net loss/gain offered by the passive repeater system.

Anyway, two of the high gain 850 MHz Yagis and a short length of low loss cable would run about $200, which we can probably justify for an experiment.

Any further advice on estimating the potential resulting signal strength at camp?