I got my first licence with the callsign OL1API in 1971. At that time, novice licences in our country were issued with OL prefixes to youngsters between 15 and 18 years of age and 160m was the only band that OL's were allowed to use.

In those days callsigns were issued in alphabetical and chronological order and other rules were followed in callsign prefixes and suffixes (what a contrast to the present mess). Furthermore, the OL1 through OL0 prefixes, as well as OK suffix letters strictly corresponded to the districts or regions of the country. Hence we could tell immidiately where the other station was from and how long it was licenced.
The below system was used for new OK/OL licences with 3 letter suffix from the 60s until the 90s. Some of the present calls still correspond to that system.

OL1..., OK1F.. Central Bohemia; OK1D.. Praha; OL2..., OK1H.. South Bohemia; OL3..., OK1I.. West Bohemia;
OL4..., OK1J.. North Bohemia; OL5..., OK1M.. East Bohemia; OL6..., OK2P.. South Moravia; OL7..., OK2S.. North Moravia;
OL8..., OK3T.. West Slovakia; OL9..., OK3Y.. Central Slovakia; OL0..., OK3Z.. East Slovakia.
OK1A.. (Bohemia), OK2B.. (Moravia), OK3C.. (Slovakia); all club stations were 3 letter suffix starting with K, O or R.

If some one operated away from the fixed QTH, it was clearly indicated by /P or /1 for portable or /A for alternative QTH. If German stations had an alternative QTH they did not sign /A but they added the letter A to the callsign, so e.g. DL9KRA and DJ4KWA were DL9KR and DJ4KW at their other QTHs.
"My" generation of early 70s fellow topbanders were the OL1AFx through OL1AZx, as well as G3Xxx through G4Bxx In Britain it was just the time when G3+3 letters block was used up and G4Axx, G4Bxx started being issued.
Hence the most contacts we were making outside of OK were with these fresh British licensees.
We could also hear respecful old timers with two letter suffix calls. As no special calls, no contest calls or vanity calls existed then, the short callsigns always indicated old timers.

The equipment
Hams in the 70s still used plenty of home built equipment and equipment building was an integral part of the hobby. In the eastern block countries this was even more pronounced as no commercial equipment was available.
Separate RX and TX were still used, this means that one would first find a station on the RX, then use netting (as we called it the "TX silent tuning") with no power to antenna to tune the TX to the same frequency as RX and then start transmitting. Some skill was needed to tune to the zero beat or correct pitch of the receive signal, otherwise you would not be heard.
I built my first TX with 6AC7 at the VFO and 6F6 at the PA stage (or Russian equivalents). Apart from home built transmitters and other station accessories we used a lot of ex-WW2 or 1950s surplus military receivers, mostly Czechoslovakian, German, Russian and some American.
My first receiver was a robust German WW2 straight receiver Torn E.b. with 4 battery tubes (valves) RV1,2P800. In order to receive CW with best sensitivity on this RX one had to carefully adjust the feedback so that oscillations just started.
Later I used Philips CR-101 RX and American RCA AR-88F which I still keep until today. I later used the AR-88's local oscillator signal and built a transceive adaptor to it (see Equipment).
In Czechoslovakia a number of the German WW2 receivers were more or less spread among hams. The aircraft "cube" receivers EK10 (E10aK), EZ6, with home made convertors, but especially the long wave RX E10L (EL10) that were widely modified for 160m and used by many OL and OK hams. These receivers were made in the shape of a 10 inch cube (approx. 24x24x24cm). Mechanically they were made of several blocks with connectors so the maintenance was easy, also they all used one single type of miracle valve RV12P2000. Although not using any crystal filters their selectivity was very good, thanks to the high-Q IF LC filters on 130kHz.
I used the modified E10L for many years and I regret that I got rid of it in the 90s.

The luckier hams in the west could buy commercial equipment like the British KW-2000, (which could be easily recognized on the band due to its slightly chirpy note), the Japanese Yaesu Musen FT101B or FR101/FL101 twins, (Sommerkamp FT277B in the German speaking countries), Kenwood R599/T599 (Trio in the UK), or some great RIGs from the USA as the Drake line, Collins twins or KWM2 transceivers etc.
I remember when in those years my father got a Collins catalog with photos on a glossy paper of KMW2 transceiver and the top class 75S3B receiver. These RIGs were just a dream to me.

The QSOs, local and DX
Outside of contests much more "normal" contacts used to be heard on Topband. People were letting their fingers talk, hand straight keys were used as well as home made electronic keyers and a lot of "rag chew" QSOs could be heard on the band. Again, what a contrast to the present time when we mostly hear "rubber stamp" or super shorty "599" QSOs.

The level of 160m activity in early 1970s proves my score in the CQ WW 160m contest in 1973 when I made 145 QSOs with 8 countries, while the top scores were possibly not more than double of that.

DX was rare and difficult to work. With the exception of a few lucky guys with big antennas (and much more than the legal power), most ordinary 10W stations with city or small lot antennas had weak signals and it took a lot of patience and luck to work anything outside Europe.
Looking through my old log I recall the moments when I was tuning the band looking for the weak DX signals.
The first DX I heard on 160m were W4EX and K1PBW on 10th January 1972. Another note in the old log shows 4W1AE, KV4FZ, WA4DUS, K1PBW/1 and K8IBQ heard on 10/12/72 . I called them many times in vain. There was little chance to work them with 8 Watts and a quarter wave horizontal end fed wire 12m high, tuned with a simple tuner against the "ground " consisiting of iron pipes of the central heating in a suburban block of flats.

DXing was different. DX contacts were made split, i.e. American stations operated in the DX window 1800-1810 kHz and Europe in the EU window 1825-1830 kHz. JAs were only allowed a narrow segment of 1906-1912 kHz. A DX calling CQ would always tell QSX frequency where they listened in the EU window.

The first real DX I worked with the simple low power set up were EP2BQ (now ZL2SQ) and KV4FZ during the CQ WW DX 1973, followed by 4X4NJ a week later. I was happy as you could imagine.

The old paper logs are sometimes good reading. They bring back memories and experiences from the band and remind the friends we used to talk to. As I used to write all the received message into the log I can now read what we were discussing on Topband over 40 years ago.

One of the memorable QSOs was one on 27/5/72 with Jim GM3IAA from Inverness (now Silent Key). Jim was ex VS1AA and the QSO and subsequent correspondence and reading of antenna literature inspired me to change my antenna from the end fed wire to VS1AA antenna, a modified Windom (today also called OCF off-centre-fed antenna).
The original VS1AA was a 41m long horizontal wire, half wave on 80m, fed in one third of its length. It was a good all band antenna that started my long time usage of OCF antennas throughout the years.
On 160m this 41m VS1AA was not an ideal radiator though, it worked as a kind of semi vertical with asymetrical top hat, fed against the ground. Anyway, it fit within the available space I had then and it worked.
In another QSO some years later (14/3/76) GM3IAA told me that on 160m he had been using a full size topband VS1AA antenna 261ft (79.55m) long, 50ft (15m) up, feeder 118ft (36m) long, all made of aluminium wire.
My original VS1AA antenna from 1972 is still up in the air at my old QTH after all those years, and was used by my father OK1DJD until he passed away in 2013.

My OL1API licence expired in 1974. My log shows that by then I had made 2829 QSOs with 21 countries on 160m.

In 1975, under my new callsign OK1DKW, I made my first US QSOs on 160m with the most active US DXer Ernie K1PBW (on 23/11/75) and with the Topband legend Stew Perry W1BB/1.
More QSOs with W8LRL,K1RQE, XN1KE (VO1KE) followed shortly, later in 1976 VE1ASJ 10/1/76, K1PBW 2/1/76, 10/1/76, 13/2/76, 26/2/76, W1HGT 8/2/76, WA4LDM 27/2/76. On 11/1/76 I worked 9H1AV for a new one, a rare country then.
The CQ 160m contest in January 1976 yielded in 146 QSOs with 14 countries, 2 DX were worked K1PBW and KV4FZ.
Still using restricted antenna and very low power, the 41m VS1AA antenna at 12m and 10 Watts.
As I have always observed the rules, it was not easy to work DX and new countries or win contests. But the well deserved achievements brought more pleasure and satisfaction.

As years went on, new RIGs and antennas were used, more countries appeared on 160m and the band was changing. But that was another story.