Before any VVS craft can shoot at B-29s, they have to find them. USSR is a big country
most all of their Radars were Lend Lease, or knock-offs of those US and UK sets. Much of their Radar Net at this time was not much different than the Chain Home Radar of 1940, the 'Dumbo' VHF Radar.
Before the 'Great Patriotic War' the USSR had used the very basic RUS-2 Radar, a High Frequency set(75-83Mhz) with 50-120kW power and A-Scope display. 120-150 km range These were mostly used around Leningrad and Moscow. The RUS-1 was a near complete failure during the Winter War with Finland, the -2 an improved system, but TX and RX antenna arrays had to be separated by about a half mile.
The USSR had independently discovered both the Cavity Magnetron and Klystron before the War, but were unable to utilize them, in part from the poor state of the electronics industry and official displeasure over high frequency Radar. Some developers were shot, others Gulaged.
During the War, the USSR was far more interested in the Gun Laying Radar than for Search, and copied the LL'ed British GL Mk II as the SON-2, and the US sent around 500 sets of various search and gun laying units
From an earlier post of mine from another site on early Cold War Soviet Radar Development
P-3 "Dumbo"
55kW VHF Band Early Warning
The first Soviet radar unit to the determination of 3 coordinates was built approximately end of the World War II. The radar station was called "Pegmantit 3" - or abbreviated for P 3. There were two modifications: a mobile (P-3M) and a fixed site (P-3A) version. The mobile version was built in containers on two trucks. The transmitter and and the receiving system were put in a separate container. The display still was an A-Scope. 120 km range
Dumbo /P3 used A scope displays, that need a more skilled operator to know what they are looking at.
The P-3 is pretty much a 1940 Chain Home set, with a few trick to get minor azimuth determination. These replaced the semi-Mobile RUS-2 sets used during the War, that couldn't do height-finding or low altitudes. They didn't have a domestic filler like Chain Home Low for gap fillers
Soviets didn't have the number of sets to provide the net coverage that the UK had in 1940, either.
*See Below
Cross Fork
AAA acquisition
based on British AA-4 Warning/ US SCR-602 radar; it led to the Knife Rest with PPI Scope
P-20 Token
.5 -1MW+ S-Band Early Warning/ later GCI Radar
three screen setup: Area, Sector and Height. All could not be active at same time. Similar to US AN/CPS-6 Radar, but not based on it: just similar goal and based on WWII ideas from MIT using five Emitters to determine azimuth, elevation and range. US noted 50 in operation across all the USSR in 1952, 115 the year after. CIA Reports from the mid '50s noted that these had a problem with overheating if used for more than 6 hours, and the P-3 had similar issues.
200-250km range
P-8 Knife Rest A Early Warning
75kW VHF 75kW 75km range PPI scope circular scan, first for Sov EarlyWarning Radars
P-30 Big Mesh GCI Radar, P-35 Bar Lock after improvements
E Band 1MW 180km
* The needed coverage I mentioned earlier
This is the kind of Radar Site density you need with Chain Home type gear to have chance at providing the data for plotting incoming aircraft
USSR didn't have anything close to that density in the 1948-1950 timeframe, and in WWII, did not experience much for Strategic Bombing by the Nazis to work on GCI methods as the UK had in place by 1940
Their better Radar, Token, in place of the Chain Home equivalent Dumbo, were able to do GCI out to 70 miles.
And they just had 50 of them deployed across the over 6000 mile length of the Country, with 37,000 miles of Border to watch over in 1952
UK has just 2000 miles of Border, with 50 Radar sites after the BoB
That means the USSR would need around 1000 sites for border coverage alone, and with vast amount of near empty territory, you need interior lines, like once past the Border, US ELINT Flights had marked the locations of the Radars in 1947, and was weak until the KoreanWar, where the number of sites increased dramatically